31. General-purpose timers (TIM2/TIM3/TIM4)

TIM4 is available only on STM32WBA62/64/65xx.

31.1 TIM2/TIM3/TIM4 introduction

The general-purpose timers consist of a 16-bit or 32-bit autoreload counter driven by a programmable prescaler.

They can be used for a variety of purposes, including measuring the pulse lengths of input signals ( input capture ) or generating output waveforms ( output compare and PWM ).

Pulse lengths and waveform periods can be modulated from a few microseconds to several milliseconds using the timer prescaler and the RCC clock controller prescalers.

The timers are completely independent, and do not share any resources. They can be synchronized together as described in Section 31.4.24: Timer synchronization .

31.2 TIM2/TIM3/TIM4 main features

General-purpose TIMx timer features include:

• • 16-bit or 32-bit up, down, up/down autoreload counter.
• • 16-bit programmable prescaler used to divide (also “on the fly”) the counter clock frequency by any factor between 1 and 65535.
• • Up to four independent channels for:
  • – Input capture.
  • – Output compare.
  • – PWM generation (edge- and center-aligned modes).
  • – One-pulse mode output.
• • Synchronization circuit to control the timer with external signals and to interconnect several timers.
• • Interrupt/DMA generation on the following events:
  • – Update: counter overflow/underflow, counter initialization (by software or internal/external trigger).
  • – Trigger event (counter start, stop, initialization, or count by internal/external trigger).
  • – Input capture.
  • – Output compare.
• • Supports incremental (quadrature) encoder and hall-sensor circuitry for positioning purposes.
• • Trigger input for external clock or cycle-by-cycle current management.
• • ADC synchronization for jitter-free sampling points.

31.3 TIM2/TIM3/TIM4 implementation

1. Note: 'X' = supported, '-' = not supported.

31.4 TIM2/TIM3/TIM4 functional description

31.4.1 Block diagram

Figure 249. General-purpose timer block diagram

1. 1. This feature is not available on all timers, refer to Section 31.3: TIM2/TIM3/TIM4 implementation .

31.4.2 TIM2/TIM3/TIM4 pins and internal signals

Table 291 and Table 292 in this section summarize the TIM inputs and outputs.

Table 291. TIM input/output pins

Table 292. TIM internal input/output signals

Table 292. TIM internal input/output signals (continued)

Table 293, Table 294, Table 295 and Table 296 are listing the sources connected to the tim_ti[4:1] input multiplexers.

Table 293. Interconnect to the tim_ti1 input multiplexer

1. Only available on STM32WBA62/63/65xx devices.

Table 294. Interconnect to the tim_ti2 input multiplexer

1. Only available on STM32WBA62/63/65xx devices.

Table 295. Interconnect to the tim_ti3 input multiplexer

1. Only available on STM32WBA62/63/65xx devices.

Table 297 lists the internal sources connected to the tim_etr input multiplexer.

1. Only available on STM32WBA62/64/65xx devices.

Table 298 lists the internal sources connected to the tim_etr input multiplexer.

1. Only available on STM32WBA62/63/65xx devices.

Table 299 lists the internal sources connected to the tim_ocref_clr input multiplexer.

1. Only available on STM32WBA62/63/65xx devices.

31.4.3 Time-base unit

The main block of the programmable timer is a 16-bit/32-bit counter with its related autoreload register. The counter can count up, down or both up and down. The counter clock can be divided by a prescaler.

The counter, the autoreload register and the prescaler register can be written or read by software. This is true even when the counter is running.

The time-base unit includes:

• • Counter register (TIMx_CNT)
• • Prescaler register (TIMx_PSC)
• • Autoreload register (TIMx_ARR).

The autoreload register is preloaded. Writing to or reading from the autoreload register accesses the preload register. The content of the preload register is transferred into the shadow register permanently or at each update event (UEV), depending on the autoreload preload enable bit (ARPE) in TIMx_CR1 register. The update event is sent when the counter reaches the overflow (or underflow when down-counting) and if the UDIS bit equals 0 in the TIMx_CR1 register. It can also be generated by software. The generation of the update event is described in detail for each configuration.

The counter is clocked by the prescaler output tim_cnt_ck, which is enabled only when the counter enable bit (CEN) in TIMx_CR1 register is set (refer also to the slave mode controller description to get more details on counter enabling).

Note that the actual counter enable signal CNT_EN is set one clock cycle after CEN.

Prescaler description

The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It is based on a 16-bit counter controlled through a 16-bit/32-bit register (in the TIMx_PSC register). It can be changed on the fly as this control register is buffered. The new prescaler ratio is taken into account at the next update event.

Figure 250 and Figure 251 give some examples of the counter behavior when the prescaler ratio is changed on the fly:

Figure 250. Counter timing diagram with prescaler division change from 1 to 2

Figure 251. Counter timing diagram with prescaler division change from 1 to 4

31.4.4 Counter modes

Up-counting mode

In up-counting mode, the counter counts from 0 to the autoreload value (content of the TIMx_ARR register), then restarts from 0 and generates a counter overflow event.

An update event can be generated at each counter overflow or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode controller).

The UEV event can be disabled by software by setting the UDIS bit in TIMx_CR1 register. This is to avoid updating the shadow registers while writing new values in the preload registers. Then no update event occurs until the UDIS bit has been written to 0. However, the counter restarts from 0, as well as the counter of the prescaler (but the prescale rate does not change). In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or DMA request is sent). This is to avoid generating both update and capture interrupts when clearing the counter on the capture event.

When an update event occurs, all the registers are updated and the update flag (UIF bit in TIMx_SR register) is set (depending on the URS bit):

• • The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC register).
• • The autoreload shadow register is updated with the preload value (TIMx_ARR).

The following figures show some examples of the counter behavior for different clock frequencies when TIMx_ARR = 0x36.

Figure 252. Counter timing diagram, internal clock divided by 1

Figure 253. Counter timing diagram, internal clock divided by 2

Figure 254. Counter timing diagram, internal clock divided by 4

Figure 255. Counter timing diagram, internal clock divided by N

Figure 256. Counter timing diagram, Update event when ARPE = 0 (TIMx_ARR not preloaded)

Figure 257. Counter timing diagram, Update event when ARPE = 1 (TIMx_ARR preloaded)

Down-counting mode

In down-counting mode, the counter counts from the autoreload value (content of the TIMx_ARR register) down to 0, then restarts from the autoreload value and generates a counter underflow event.

An update event can be generated at each counter underflow or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode controller)

The UEV update event can be disabled by software by setting the UDIS bit in TIMx_CR1 register. This is to avoid updating the shadow registers while writing new values in the preload registers. Then no update event occurs until UDIS bit has been written to 0. However, the counter restarts from the current autoreload value, whereas the counter of the prescaler restarts from 0 (but the prescale rate does not change).

In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or DMA request is sent). This is to avoid generating both update and capture interrupts when clearing the counter on the capture event.

When an update event occurs, all the registers are updated and the update flag (UIF bit in TIMx_SR register) is set (depending on the URS bit):

• • The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC register).
• • The autoreload active register is updated with the preload value (content of the TIMx_ARR register). Note that the autoreload is updated before the counter is reloaded, so that the next period is the expected one.

The following figures show some examples of the counter behavior for different clock frequencies when TIMx_ARR = 0x36.

Figure 258. Counter timing diagram, internal clock divided by 1

Figure 259. Counter timing diagram, internal clock divided by 2

Figure 260. Counter timing diagram, internal clock divided by 4

Figure 261. Counter timing diagram, internal clock divided by N

Figure 262. Counter timing diagram, Update event

Center-aligned mode (up/down-counting)

In center-aligned mode, the counter counts from 0 to the autoreload value (content of the TIMx_ARR register) – 1, generates a counter overflow event, then counts from the

autoreload value down to 1 and generates a counter underflow event. Then it restarts counting from 0.

Center-aligned mode is active when the CMS bits in TIMx_CR1 register are not equal to 00. The output compare interrupt flag of channels configured in output is set when: the counter counts down (Center aligned mode 1, CMS = 01), the counter counts up (Center aligned mode 2, CMS = 10) the counter counts up and down (Center aligned mode 3, CMS = 11).

In this mode, the direction bit (DIR from TIMx_CR1 register) cannot be written. It is updated by hardware and gives the current direction of the counter.

The update event can be generated at each counter overflow and at each counter underflow or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode controller) also generates an update event. In this case, the counter restarts counting from 0, as well as the counter of the prescaler.

The UEV update event can be disabled by software by setting the UDIS bit in TIMx_CR1 register. This is to avoid updating the shadow registers while writing new values in the preload registers. Then no update event occurs until the UDIS bit has been written to 0. However, the counter continues counting up and down, based on the current autoreload value.

In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or DMA request is sent). This is to avoid generating both update and capture interrupts when clearing the counter on the capture event.

When an update event occurs, all the registers are updated and the update flag (UIF bit in TIMx_SR register) is set (depending on the URS bit):

• • The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC register).
• • The autoreload active register is updated with the preload value (content of the TIMx_ARR register). Note that if the update source is a counter overflow, the autoreload is updated before the counter is reloaded, so that the next period is the expected one (the counter is loaded with the new value).

The following figures show some examples of the counter behavior for different clock frequencies.

Figure 263. Counter timing diagram, internal clock divided by 1, TIMx_ARR = 0x6

1. 1. Here, center-aligned mode 1 is used (for more details refer to Section 31.5.1: TIMx control register 1 (TIMx_CR1)(x = 2 to 4) ).

Figure 264. Counter timing diagram, internal clock divided by 2

Figure 265. Counter timing diagram, internal clock divided by 4, TIMx_ARR = 0x36

• 1. Center-aligned mode 2 or 3 is used with a UIF on overflow.

Figure 266. Counter timing diagram, internal clock divided by N

Figure 267. Counter timing diagram, Update event with ARPE = 1 (counter underflow)

Figure 268. Counter timing diagram, Update event with ARPE = 1 (counter overflow)

31.4.5 Clock selection

The counter clock can be provided by the following clock sources:

• • Internal clock (tim_ker_ck).
• • External clock mode1: external input pin (tim_ti1 or tim_ti2).
• • External clock mode2: external trigger input (tim_etr_in).
• • Internal trigger inputs (tim_itr): using one timer as prescaler for another timer, for example, timer 1 can be configured to act as a prescaler for timer 2. Refer to Using one timer as prescaler for another timer for more details.

Internal clock source (tim_ker_ck)

If the slave mode controller is disabled (SMS = 000 in the TIMx_SMCR register), then the CEN, DIR (in the TIMx_CR1 register), and UG bits (in the TIMx_EGR register) are actual control bits and can be changed only by software (except UG which remains cleared automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal clock tim_ker_ck.

Figure 269 shows the behavior of the control circuit and the upcounter in normal mode, without prescaler.

Figure 269. Control circuit in normal mode, internal clock divided by 1

External clock source mode 1

This mode is selected when SMS = 111 in the TIMx_SMCR register. The counter can count at each rising or falling edge on a selected input.

Figure 270. tim_ti2 external clock connection example

1. 1. Codes ranging from 01000 to 11111: tim_itr[15:0].

For example, to configure the upcounter to count in response to a rising edge on the tim_ti2 input, use the following procedure:

1. 1. Select the proper tim_ti2_in[15:0] source (internal or external) with the TI2SEL[3:0] bits in the TIMx_TISEL register.
2. 2. Configure channel 2 to detect rising edges on the tim_ti2 input by writing CC2S= 01 in the TIMx_CCMR1 register.
3. 3. Configure the input filter duration by writing the ICF2[3:0] bits in the TIMx_CCMR1 register (if no filter is needed, keep ICF2 = 0000).

Note: The capture prescaler is not used for triggering, so it does not need to be configured.

1. 4. Select rising edge polarity by writing CC2P = 0 and CC2NP = 0 in the TIMx_CCER register.
2. 5. Configure the timer in external clock mode 1 by writing SMS = 111 in the TIMx_SMCR register.
3. 6. Select tim_ti2 as the input source by writing TS = 00110 in the TIMx_SMCR register.
4. 7. Enable the counter by writing CEN = 1 in the TIMx_CR1 register.

When a rising edge occurs on tim_ti2, the counter counts once and the TIF flag is set.

The delay between the rising edge on tim_ti2 and the actual clock of the counter is due to the resynchronization circuit on tim_ti2 input.

Figure 271. Control circuit in external clock mode 1

External clock source mode 2

This mode is selected by writing ECE = 1 in the TIMx_SMCR register.

The counter can count at each rising or falling edge on the external trigger input tim_etr_in.

Figure 272 gives an overview of the external trigger input block.

Figure 272. External trigger input block

For example, to configure the upcounter to count each two rising edges on tim_etr_in, use the following procedure:

1. 1. Select the proper tim_etr_in source (internal or external) with the ETRSEL[3:0] bits in the TIMx_AF1 register.
2. 2. As no filter is needed in this example, write ETF[3:0] = 0000 in the TIMx_SMCR register.
3. 3. Set the prescaler by writing ETPS[1:0] = 01 in the TIMx_SMCR register.
4. 4. Select rising edge detection on the tim_etr_in by writing ETP = 0 in the TIMx_SMCR register.
5. 5. Enable external clock mode 2 by writing ECE = 1 in the TIMx_SMCR register.
6. 6. Enable the counter by writing CEN = 1 in the TIMx_CR1 register.

The counter counts once each two tim_etr_in rising edges.

The delay between the rising edge on tim_etr_in and the actual clock of the counter is due to the resynchronization circuit on the tim_etrp signal. As a consequence, the maximum frequency that can be correctly captured by the counter is at most 1/4 of tim_ker_ck frequency. When the ETRP signal is faster, the user must apply a division of the external signal by a proper ETPS prescaler setting.

Figure 273. Control circuit in external clock mode 2

31.4.6 Capture/compare channels

Each Capture/Compare channel is built around a capture/compare register (including a shadow register), an input stage for capture (with digital filter, multiplexing and prescaler) and an output stage (with comparator and output control).

The following figure gives an overview of one Capture/Compare channel.

The input stage samples the corresponding tim_tix input to generate a filtered signal tim_tixf. Then, an edge detector with polarity selection generates a signal (tim_tixfpy) which can be used as trigger input by the slave mode controller or as the capture command. It is prescaled before the capture register (ICxPS).

Figure 274. Capture/compare channel (example: channel 1 input stage)

The output stage generates an intermediate waveform which is then used for reference: tim_ocxref (active high). The polarity acts at the end of the chain.

Figure 275. Capture/compare channel 1 main circuit

Figure 276. Output stage of capture/compare channel (channel 1, idem ch.2, 3 and 4)

1. Available on some instances only. If not available, tim_etr is directly connected to tim_ocref_clr_int .

The capture/compare block is made of one preload register and one shadow register. Write and read always access the preload register.

In capture mode, captures are actually done in the shadow register, which is copied into the preload register.

In compare mode, the content of the preload register is copied into the shadow register which is compared to the counter.

31.4.7 Input capture mode

In input capture mode, the capture/compare registers (TIMx_CCRx) are used to latch the value of the counter after a transition detected by the corresponding ICx signal. When a capture occurs, the corresponding CCxIF flag (TIMx_SR register) is set and an interrupt or a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was already high, then the overcapture flag CCxOF (TIMx_SR register) is set. CCxIF can be cleared by software by writing it to 0 or by reading the captured data stored in the TIMx_CCRx register. CCxOF is cleared when it is written with 0.

The following example shows how to capture the counter value in TIMx_CCR1 when tim_ti1 input rises. To do this, use the following procedure:

1. 1. Select the proper tim_tix_in[15:0] source (internal or external) with the TI1SEL[3:0] bits in the TIMx_TISEL register.
2. 2. Select the active input: TIMx_CCR1 must be linked to the tim_ti1 input, so write the CC1S bits to 01 in the TIMx_CCMR1 register. As soon as CC1S becomes different from 00, the channel is configured in input and the TIMx_CCR1 register becomes read-only.
3. 3. Program the needed input filter duration in relation with the signal connected to the timer (when the input is one of the tim_tix (ICxF bits in the TIMx_CCMRx register). Let's imagine that, when toggling, the input signal is not stable during at most five internal clock cycles. We must program a filter duration longer than these five clock cycles. We can validate a transition on tim_ti1 when eight consecutive samples with the new level have been detected (sampled at \( f_{DTS} \) frequency). Then write IC1F bits to 0011 in the TIMx_CCMR1 register.
4. 4. Select the edge of the active transition on the tim_ti1 channel by writing the CC1P and CC1NP bits to 000 in the TIMx_CCER register (rising edge in this case).
5. 5. Program the input prescaler. In this example, the capture is to be performed at each valid transition, so the prescaler is disabled (write IC1PS bits to 00 in the TIMx_CCMR1 register).
6. 6. Enable capture from the counter into the capture register by setting the CC1E bit in the TIMx_CCER register.
7. 7. If needed, enable the related interrupt request by setting the CC1IE bit in the TIMx_DIER register, and/or the DMA request by setting the CC1DE bit in the TIMx_DIER register.

When an input capture occurs:

• • The TIMx_CCR1 register gets the value of the counter on the active transition.
• • CC1IF flag is set (interrupt flag). CC1OF is also set if at least two consecutive captures occurred whereas the flag was not cleared.
• • An interrupt is generated depending on the CC1IE bit.
• • A DMA request is generated depending on the CC1DE bit.

In order to handle the overcapture, it is recommended to read the data before the overcapture flag. This is to avoid missing an overcapture which may happen after reading the flag and before reading the data.

Note: IC interrupt and/or DMA requests can be generated by software by setting the corresponding CCxG bit in the TIMx_EGR register.

31.4.8 PWM input mode

This mode is used to measure both the period and the duty cycle of a PWM signal connected to single tim_tix input:

• • The TIMx_CCR1 register holds the period value (interval between two consecutive rising edges).
• • The TIMx_CCR2 register holds the pulse width (interval between two consecutive rising and falling edges).

This mode is a particular case of input capture mode. The set-up procedure is similar with the following differences:

• • Two ICx signals are mapped on the same tim_tix input.
• • These two ICx signals are active on edges with opposite polarity.
• • One of the two TIxFP signals is selected as trigger input and the slave mode controller is configured in reset mode.

The period and the pulse width of a PWM signal applied on tim_ti1 can be measured using the following procedure:

1. 1. Select the proper tim_tix_in[15:0] source (internal or external) with the TI1SEL[3:0] bits in the TIMx_TISEL register.
2. 2. Select the active input for TIMx_CCR1: write the CC1S bits to 01 in the TIMx_CCMR1 register (tim_ti1 selected).
3. 3. Select the active polarity for tim_ti1fp1 (used both for capture in TIMx_CCR1 and counter clear): write the CC1P to 0 and the CC1NP bit to 0 (active on rising edge).
4. 4. Select the active input for TIMx_CCR2: write the CC2S bits to 10 in the TIMx_CCMR1 register (tim_ti1 selected).
5. 5. Select the active polarity for tim_ti1fp2 (used for capture in TIMx_CCR2): write the CC2P bit to 1 and the CC2NP bit to 0 (active on falling edge).
6. 6. Select the valid trigger input: write the TS bits to 00101 in the TIMx_SMCR register (tim_ti1fp1 selected).
7. 7. Configure the slave mode controller in reset mode: write the SMS bits to 100 in the TIMx_SMCR register.
8. 8. Enable the captures: write the CC1E and CC2E bits to 1 in the TIMx_CCER register.

Figure 277. PWM input mode timing

1. 1. The PWM input mode can be used only with the TIMx_CH1/TIMx_CH2 signals due to the fact that only tim_ti1fp1 and tim_ti2fp2 are connected to the slave mode controller.

31.4.9 Forced output mode

In output mode (CCxS bits = 00 in the TIMx_CCMRx register), each output compare signal (tim_ocxref and then tim_ocx) can be forced to active or inactive level directly by software, independently of any comparison between the output compare register and the counter.

To force an output compare signal (tim_ocxref/tim_ocx) to its active level, the user just needs to write 101 in the OCxM bits in the corresponding TIMx_CCMRx register. Thus tim_ocxref is forced high (tim_ocxref is always active high) and tim_ocx get opposite value to CCxP polarity bit.

For example: CCxP = 0 (tim_ocx active high) => tim_ocx is forced to high level.

tim_ocxref signal can be forced low by writing the OCxM bits to 100 in the TIMx_CCMRx register.

Anyway, the comparison between the TIMx_CCRx shadow register and the counter is still performed and allows the flag to be set. Interrupt and DMA requests can be sent accordingly. This is described in the Output Compare mode section.

31.4.10 Output compare mode

This function is used to control an output waveform or indicating when a period of time has elapsed.

When a match is found between the capture/compare register and the counter, the output compare function:

• • Assigns the corresponding output pin to a programmable value defined by the output compare mode (OCxM bits in the TIMx_CCMRx register) and the output polarity (CCxP bit in the TIMx_CCER register). The output pin can keep its level (OCXM = 000), be set

active (OCxM = 001), be set inactive (OCxM = 010) or can toggle (OCxM = 011) on match.

• • Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).
• • Generates an interrupt if the corresponding interrupt mask is set (CCXIE bit in the TIMx_DIER register).
• • Sends a DMA request if the corresponding enable bit is set (CCxDE bit in the TIMx_DIER register, CCDS bit in the TIMx_CR2 register for the DMA request selection).

The TIMx_CCRx registers can be programmed with or without preload registers using the OCxPE bit in the TIMx_CCMRx register.

In output compare mode, the update event UEV has no effect on tim_ocxref and tim_ocx output. The timing resolution is one count of the counter. Output compare mode can also be used to output a single pulse (in One-pulse mode).

Procedure

1. 1. Select the counter clock (internal, external, prescaler).
2. 2. Write the desired data in the TIMx_ARR and TIMx_CCRx registers.
3. 3. Set the CCxIE and/or CCxDE bits if an interrupt and/or a DMA request is to be generated.
4. 4. Select the output mode. For example:
   1. a) Write OCxM = 0011 to toggle tim_ocx output pin when CNT matches CCRx.
   2. b) Write OCxPE = 0 to disable preload register.
   3. c) Write CCxP = 0 to select active high polarity.
   4. d) Write CCxE = 1 to enable the output.
5. 5. Enable the counter by setting the CEN bit in the TIMx_CR1 register.

The TIMx_CCRx register can be updated at any time by software to control the output waveform, provided that the preload register is not enabled (OCxPE = 0, else TIMx_CCRx shadow register is updated only at the next update event UEV). An example is given in Figure 278 .

Figure 278. Output compare mode, toggle on tim_oc1

31.4.11 PWM mode

Pulse width modulation mode is used to generate a signal with a frequency determined by the value of the TIMx_ARR register and a duty cycle determined by the value of the TIMx_CCRx register.

The PWM mode can be selected independently on each channel (one PWM per tim_ocx output) by writing 110 (PWM mode 1) or 111 (PWM mode 2) in the OCxM bits in the TIMx_CCMRx register. The corresponding preload register must be enabled by setting the OCxPE bit in the TIMx_CCMRx register, and eventually the autoreload preload register (in up-counting or center-aligned modes) by setting the ARPE bit in the TIMx_CR1 register.

As the preload registers are transferred to the shadow registers only when an update event occurs, before starting the counter, all registers must be initialized by setting the UG bit in the TIMx_EGR register.

tim_ocx polarity is software programmable using the CCxP bit in the TIMx_CCER register. It can be programmed as active high or active low. tim_ocx output is enabled by the CCxE bit in the TIMx_CCER register. Refer to the TIMx_CCERx register description for more details.

In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine whether \( TIMx\_CCRx \leq TIMx\_CNT \) or \( TIMx\_CNT \leq TIMx\_CCRx \) (depending on the direction of the counter). The tim_ocref_clr can be cleared by an external event through the tim_etr_in or the tim_ocref_clr signals. In this case the tim_ocref_clr signal is asserted only:

• • After a compare match event.
• • When the output compare mode (OCxM bits in TIMx_CCMRx register) switches from the “frozen” configuration (no comparison, OCxM = 000) to one of the PWM modes (OCxM = 110 or 111). This forces the PWM by software while the timer is running.

The timer is able to generate PWM in edge-aligned mode or center-aligned mode depending on the CMS bits in the TIMx_CR1 register.

PWM edge-aligned mode

• • Up-counting configuration
• • Up-counting is active when the DIR bit in the TIMx_CR1 register is low. Refer to Up-counting mode .

In the following example, we consider PWM mode 1. The reference PWM signal tim_ocxref is high as long as TIMx_CNT < TIMx_CCRx else it becomes low. If the compare value in TIMx_CCRx is greater than the autoreload value (in TIMx_ARR) then tim_ocxref is held at 1. If the compare value is 0 then tim_ocxref is held at 0. Figure 279 shows some edge-aligned PWM waveforms in an example where TIMx_ARR = 8.

Figure 279. Edge-aligned PWM waveforms (ARR = 8)

Down-counting configuration

• • Down-counting is active when DIR bit in TIMx_CR1 register is high. Refer to Down-counting mode .

In PWM mode 1, the reference signal tim_ocxref is low as long as TIMx_CNT > TIMx_CCRx else it becomes high. If the compare value in TIMx_CCRx is greater than the autoreload value in TIMx_ARR, then tim_ocxref is held at 100%. PWM is not possible in this mode.

PWM center-aligned mode

Center-aligned mode is active when the CMS bits in TIMx_CR1 register are different from 00 (all the remaining configurations having the same effect on the tim_ocxref/tim_ocx signals). The compare flag is set when the counter counts up, when it counts down or both when it counts up and down depending on the CMS bits configuration. The direction bit

(DIR) in the TIMx_CR1 register is updated by hardware and must not be changed by software. Refer to Center-aligned mode (up/down-counting) .

Figure 280 shows some center-aligned PWM waveforms in an example where:

• • TIMx_ARR = 8.
• • PWM mode is the PWM mode 1.
• • The flag is set when the counter counts down corresponding to the center-aligned mode 1 selected for CMS = 01 in TIMx_CR1 register.

Figure 280. Center-aligned PWM waveforms (ARR = 8)

Hints on using center-aligned mode:

• • When starting in center-aligned mode, the current up-down configuration is used. It means that the counter counts up or down depending on the value written in the DIR bit

in the TIMx_CR1 register. Moreover, the DIR and CMS bits must not be changed at the same time by the software.

• • Writing to the counter while running in center-aligned mode is not recommended as it can lead to unexpected results. In particular:
  • – The direction is not updated if a value greater than the autoreload value is written in the counter (TIMx_CNT > TIMx_ARR). For example, if the counter was counting up, it continues to count up.
  • – The direction is updated if 0 or the TIMx_ARR value is written in the counter but no update event UEV is generated.
• • The safest way to use center-aligned mode is to generate an update by software (setting the UG bit in the TIMx_EGR register) just before starting the counter and not to write the counter while it is running.

Dithering mode

The PWM mode effective resolution can be increased by enabling the dithering mode, using the DITHEN bit in the TIMx_CR1 register. This applies to both the CCR (for duty cycle resolution increase) and ARR (for PWM frequency resolution increase).

The operating principle is to have the actual CCR (or ARR) value slightly changed (adding or not one timer clock period) over 16 consecutive PWM periods, with predefined patterns. This allows a 16-fold resolution increase, considering the average duty cycle or PWM period. Figure 281 presents the dithering principle applied to four consecutive PWM cycles.

Figure 281. Dithering principle

When the dithering mode is enabled, the register coding is changed as following (see Figure 282 for example):

• • The four LSBs are coding for the enhanced resolution part (fractional part).
• • The MSBs are left-shifted by four places and are coding for the base value. In 16-bit mode, the 16-bit format is maintained.

Note: The following sequence must be followed when resetting the DITHEN bit:

1. 1. CEN and ARPE bits must be reset.
2. 2. The DITHEN bit must be reset.
3. 3. The CCIF flags must be cleared.
4. 4. The CEN bit can be set (eventually with ARPE = 1).

Figure 282. Data format and register coding in dithering mode

The minimum frequency is given by the following formula:

Note: For 16-bit timers, the maximum TIMx_ARR and TIMx_CCRy values are limited to 0xFFFEF in dithering mode (corresponds to 65534 for the integer part and 15 for the dithered part). For 32-bit timers, the maximum TIMx_ARR and TIMx_CCRy values are limited to

0xFFFFFFEF in dithering mode (corresponds to 264435454 for the integer part and 15 for the dithered part).

As shown on Figure 283 and Figure 284 , the dithering mode is used to increase the PWM resolution.

Figure 283. PWM resolution vs frequency (16-bit mode)

Figure 284. PWM resolution vs frequency (32-bit mode)

The duty cycle and/or period changes are spread over 16 consecutive periods, as described in Figure 285 .

Figure 285. PWM dithering pattern

The autoreload and compare values increments are spread following specific patterns described in Table 300 . The dithering sequence is done to have increments distributed as evenly as possible and minimize the overall ripple.

Table 300. CCR and ARR register change dithering pattern

The dithering mode is also available in center-aligned PWM mode (CMS bits in TIMx_CR1 register are not equal to 00). In this case, the dithering pattern is applied over eight consecutive PWM periods, considering the up and down-counting phases as shown in Figure 286.

Figure 286. Dithering effect on duty cycle in center-aligned PWM mode

MSV50904V1

Table 301 shows how the dithering pattern is added in center-aligned PWM mode.

Table 301. CCR register change dithering pattern in center-aligned PWM mode

31.4.12 Asymmetric PWM mode

Asymmetric mode allows two center-aligned PWM signals to be generated with a programmable phase shift. While the frequency is determined by the value of the TIMx_ARR register, the duty cycle and the phase-shift are determined by a pair of TIMx_CCRx registers. One register controls the PWM during up-counting, the second during down-counting, so that PWM is adjusted every half PWM cycle:

• • tim_oc1refc (or tim_oc2refc) is controlled by TIMx_CCR1 and TIMx_CCR2.
• • tim_oc3refc (or tim_oc4refc) is controlled by TIMx_CCR3 and TIMx_CCR4.

Asymmetric PWM mode can be selected independently on two channels (one tim_ocx output per pair of CCR registers) by writing 1110 (Asymmetric PWM mode 1) or 1111 (Asymmetric PWM mode 2) in the OCxM bits in the TIMx_CCMRx register.

Note: The OCxM[3:0] bitfield is split into two parts for compatibility reasons, the most significant bit is not contiguous with the three least significant ones.

When a given channel is used as asymmetric PWM channel, its secondary channel can also be used. For instance, if an tim_oc1refc signal is generated on channel 1 (Asymmetric PWM mode 1), it is possible to output either the tim_oc2ref signal on channel 2, or an tim_oc2refc signal resulting from asymmetric PWM mode 2.

Figure 287 shows an example of signals that can be generated using asymmetric PWM mode (channels 1 to 4 are configured in asymmetric PWM mode 2).

Figure 287. Generation of two phase-shifted PWM signals with 50% duty cycle

31.4.13 Combined PWM mode

Combined PWM mode allows two edge or center-aligned PWM signals to be generated with programmable delay and phase shift between respective pulses. While the frequency is determined by the value of the TIMx_ARR register, the duty cycle and delay are determined by the two TIMx_CCRx registers. The resulting signals, tim_ocxrefc, are made of an OR or AND logical combination of two reference PWMs:

• • tim_oc1refc (or tim_oc2refc) is controlled by TIMx_CCR1 and TIMx_CCR2
• • tim_oc3refc (or tim_oc4refc) is controlled by TIMx_CCR3 and TIMx_CCR4

Combined PWM mode can be selected independently on two channels (one tim_ocx output per pair of CCR registers) by writing 1100 (Combined PWM mode 1) or 1101 (Combined PWM mode 2) in the OCxM bits in the TIMx_CCMRx register.

When a given channel is used as combined PWM channel, its secondary channel must be configured in the opposite PWM mode (for instance, one in Combined PWM mode 1 and the other in Combined PWM mode 2).

Note: The OCxM[3:0] bitfield is split into two parts for compatibility reasons, the most significant bit is not contiguous with the three least significant ones.

Figure 288 shows an example of signals that can be generated using combined PWM mode, obtained with the following configuration:

• • Channel 1 is configured in Combined PWM mode 1.
• • Channel 2 is configured in PWM mode 2.
• • Channel 3 is configured in Combined PWM mode 2.
• • Channel 4 is configured in PWM mode 1.

Figure 288. Combined PWM mode on channels 1 and 3

31.4.14 Clearing the \( tim\_ocxref \) signal on an external event

The \( tim\_ocxref \) signal of a given channel can be cleared when a high level is applied on the \( tim\_ocref\_clr\_int \) input (OCxCE enable bit in the corresponding TIMx_CCMRx register set to 1). \( tim\_ocxref \) remains low until the next transition to the active state, on the following PWM cycle. This function can only be used in Output compare and PWM modes. It does not work in Forced mode.

The \( tim\_ocref\_clr\_int \) source depends on the OCREF clear selection feature implementation, refer to Section 31.3: TIM2/TIM3/TIM4 implementation .

If the OCREF clear selection feature is implemented, the \( tim\_ocref\_clr\_int \) can be selected between the \( tim\_ocref\_clr \) input and the \( tim\_etr \) input ( \( tim\_etr\_in \) after the filter) by configuring the OCCS bit in the TIMx_SMCR register. The \( tim\_ocref\_clr \) input can be selected among several \( tim\_ocref\_clr[7:0] \) inputs, using the OCRSEL[2:0] bitfield in the TIMx_AF2 register, as shown in Figure 289 .

Figure 289. OCREF_CLR input selection multiplexer

If the OCREF clear selection feature is not implemented, the tim_ocref_clr_int input is directly connected to the tim_etrf input.

For example, the tim_ocref_clr_int signal can be connected to the output of a comparator to be used for current handling. In this case, tim_etr_in must be configured as follows:

1. 1. The external trigger prescaler must be kept off: bits ETPS[1:0] in the TIMx_SMCR register are cleared to 00.
2. 2. The external clock mode 2 must be disabled: bit ECE in the TIMx_SMCR register is cleared to 0.
3. 3. The external trigger polarity (ETP) and the external trigger filter (ETF) can be configured according to the application's needs.

Figure 290 shows the behavior of the tim_ocref signal when the tim_etrf input becomes high, for both values of the OCxCE enable bit. In this example, the timer TIMx is programmed in PWM mode.

Figure 290. Clearing TIMx tim_ocref

Note: In case of a PWM with a 100% duty cycle (if CCRx>ARR), tim_ocxref is enabled again at the next counter overflow.

31.4.15 One-pulse mode

One-pulse mode (OPM) is a particular case of the previous modes. It allows the counter to be started in response to a stimulus and to generate a pulse with a programmable length after a programmable delay.

Starting the counter can be controlled through the slave mode controller. Generating the waveform can be done in output compare mode or PWM mode. One-pulse mode is selected by setting the OPM bit in the TIMx_CR1 register. This makes the counter stop automatically at the next update event UEV.

A pulse can be correctly generated only if the compare value is different from the counter initial value. Before starting (when the timer is waiting for the trigger), the configuration must be:

CNT < CCRx ≤ ARR (in particular, 0 < CCRx).

Figure 291. Example of One-pulse mode

For example if the user wants to generate a positive pulse on tim_oc1 with a length of t_PULSE and after a delay of t_DELAY as soon as a positive edge is detected on the tim_ti2 input pin.

Use tim_ti2fp2 as trigger 1:

1. 1. Select the proper tim_ti2_in[15:0] source (internal or external) with the TI2SEL[3:0] bits in the TIMx_TISEL register.
2. 2. Map tim_ti2fp2 on tim_ti2 by writing CC2S = 01 in the TIMx_CCMR1 register.
3. 3. tim_ti2fp2 must detect a rising edge, write CC2P = 0 and CC2NP = 0 in the TIMx_CCER register.
4. 4. Configure tim_ti2fp2 as trigger for the slave mode controller (tim_trgi) by writing TS = 00110 in the TIMx_SMCR register.
5. 5. tim_ti2fp2 is used to start the counter by writing SMS to 110 in the TIMx_SMCR register (trigger mode).

The OPM waveform is defined by writing the compare registers (taking into account the clock frequency and the counter prescaler).

• • The \( t_{\text{DELAY}} \) is defined by the value written in the TIMx_CCR1 register.
• • The \( t_{\text{PULSE}} \) is defined by the difference between the autoreload value and the compare value (TIMx_ARR - TIMx_CCR1).
• • Suppose the user wants to build a waveform with a transition from 0 to 1 when a compare match occurs and a transition from 1 to 0 when the counter reaches the autoreload value. To do this PWM mode 2 must be enabled by writing OC1M = 111 in the TIMx_CCMR1 register. Optionally the preload registers can be enabled by writing OC1PE = 1 in the TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this case one has to write the compare value in the TIMx_CCR1 register, the autoreload value in the TIMx_ARR register, generate an update by setting the UG bit and wait for external trigger event on tim_ti2. CC1P is written to 0 in this example.

In this example, the DIR and CMS bits in the TIMx_CR1 register must be low.

Since only one pulse (Single mode) is needed, a one must be written in the OPM bit in the TIMx_CR1 register to stop the counter at the next update event (when the counter rolls over from the autoreload value back to 0). When OPM bit in the TIMx_CR1 register is set to 0, so the Repetitive mode is selected.

Particular case: tim_ocx fast enable:

In One-pulse mode, the edge detection on tim_tix input set the CEN bit which enables the counter. Then the comparison between the counter and the compare value makes the output toggle. But several clock cycles are needed for these operations and it limits the minimum delay \( t_{\text{DELAY}} \) min we can get.

If one wants to output a waveform with the minimum delay, the OCxFE bit can be set in the TIMx_CCMRx register. Then tim_ocxref (and tim_ocx) is forced in response to the stimulus, without taking in account the comparison. Its new level is the same as if a compare match had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.

31.4.16 Retriggerable one-pulse mode

This mode allows the counter to be started in response to a stimulus and to generate a pulse with a programmable length, but with the following differences with non-retriggerable one-pulse mode described in Section 31.4.15 :

• • The pulse starts as soon as the trigger occurs (no programmable delay).
• • The pulse is extended if a new trigger occurs before the previous one is completed.

The timer must be in Slave mode, with the bits SMS[3:0] = 1000 (Combined Reset + trigger mode) in the TIMx_SMCR register, and the OCxM[3:0] bits set to 1000 or 1001 for Retriggerable OPM mode 1 or 2.

If the timer is configured in Up-counting mode, the corresponding CCRx must be set to 0 (the ARR register sets the pulse length). If the timer is configured in down-counting mode CCRx must be above or equal to ARR.

Note: In Retriggerable one-pulse mode, the CCxIF flag is not significant.

The OCxM[3:0] and SMS[3:0] bitfields are split into two parts for compatibility reasons, the most significant bit is not contiguous with the three least significant ones.

This mode must not be used with center-aligned PWM modes. It is mandatory to have CMS[1:0] = 00 in TIMx_CR1.

Figure 292. Retriggerable one-pulse mode

31.4.17 Pulse on compare mode

A pulse can be generated upon compare match event. A signal with a programmable pulse width generated when the counter value equals a given compare value, for debugging or synchronization purposes.

This mode is available for any slave mode selection, including encoder modes, in edge and center aligned counting modes. It is solely available for channel 3 and channel 4. The pulse generator is unique and is shared by the two channels, as shown on Figure 293 .

Figure 293. Pulse generator circuitry

Figure 294 shows how the pulse is generated for edge-aligned and encoder operating modes.

Figure 294. Pulse generation on compare event, for edge-aligned and encoder modes

This output compare mode is selected using the OC3M[3:0] and OC4M[3:0] bitfields in TIMx_CCMR2 register.

The pulse width is programmed using the PW[7:0] bitfield in the register, using a specific clock prescaled according to PWPRSC[2:0] bits, as follows:

gives the resolution and maximum values depending on the prescaler value.

The pulse is retriggerable: a new trigger while the pulse is ongoing, causes the pulse to be extended.

Note: If the two channels are enabled simultaneously, the pulses are issued independently as long as the trigger on one channel is not overlapping the pulse generated on the concurrent output. On the opposite, if the two triggers are overlapping, the pulse width related to the first arriving trigger is extended (because of the retrigger), while the pulse width of the last arriving trigger is correct (as shown on Figure 295).

Figure 295. Extended pulse width in case of concurrent triggers

31.4.18 Encoder interface mode

Quadrature encoder

To select Encoder interface mode write SMS = 0001 in the TIMx_SMCR register if the counter is counting on tim_ti1 edges only, SMS = 0010 if it is counting on tim_ti2 edges only and SMS = 0011 if it is counting on both tim_ti1 and tim_ti2 edges.

Select the tim_ti1 and tim_ti2 polarity by programming the CC1P and CC2P bits in the TIMx_CCER register. CC1NP and CC2NP must be kept cleared. When needed, the input filter can be programmed as well.

The two inputs tim_ti1 and tim_ti2 are used to interface to an incremental encoder. Refer to Table 302 . The counter is clocked by each valid transition on tim_ti1fp1 or tim_ti2fp2 (tim_ti1 and tim_ti2 after input filter and polarity selection, tim_ti1fp1 = tim_ti1 if not filtered and not inverted, tim_ti2fp2 = tim_ti2 if not filtered and not inverted) assuming that it is enabled (CEN bit in TIMx_CR1 register written to 1). The sequence of transitions of the two inputs is evaluated and generates count pulses as well as the direction signal. Depending on the sequence the counter counts up or down, the DIR bit in the TIMx_CR1 register is modified by hardware accordingly. The DIR bit is calculated at each transition on any input (tim_ti1 or

tim_ti2), whatever the counter is counting on tim_ti1 only, tim_ti2 only or both tim_ti1 and tim_ti2.

Encoder interface mode acts simply as an external clock with direction selection. This means that the counter just counts continuously between 0 and the autoreload value in the TIMx_ARR register (0 to ARR or ARR down to 0 depending on the direction). So the TIMx_ARR must be configured before starting. In the same way, the capture, compare, prescaler, trigger output features continue to work as normal. Encoder mode and External clock mode 2 are not compatible and must not be selected together.

In this mode, the counter is modified automatically following the speed and the direction of the quadrature encoder and its content, therefore, always represents the encoder's position. The count direction corresponds to the rotation direction of the connected sensor. The table summarizes the possible combinations, assuming tim_ti1 and tim_ti2 do not switch at the same time.

Table 302. Counting direction versus encoder signals(CC1P = CC2P = 0)

A quadrature encoder can be connected directly to the MCU without external interface logic. However, comparators are normally used to convert the encoder's differential outputs to digital signals. This greatly increases noise immunity. The third encoder output which indicates the mechanical zero position, can be connected to the external trigger input and trigger a counter reset.

Figure 296 gives an example of counter operation, showing count signal generation and direction control. It also shows how input jitter is compensated where both edges are

selected. This might occur if the sensor is positioned near to one of the switching points. For this example we assume that the configuration is the following:

• • CC1S = 01 (TIMx_CCMR1 register, tim_ti1fp1 mapped on tim_ti1).
• • CC2S = 01 (TIMx_CCMR1 register, tim_ti2fp2 mapped on tim_ti2).
• • CC1P and CC1NP = 0 (TIMx_CCER register, tim_ti1fp1 noninverted, tim_ti1fp1 = tim_ti1).
• • CC2P and CC2NP = 0 (TIMx_CCER register, tim_ti2fp2 noninverted, tim_ti2fp2 = tim_ti2).
• • SMS = 0011 (TIMx_SMCR register, both inputs are active on both rising and falling edges).
• • CEN = 1 (TIMx_CR1 register, counter is enabled).

Figure 296. Example of counter operation in encoder interface mode

Figure 297 gives an example of counter behavior when tim_ti1fp1 polarity is inverted (same configuration as above except CC1P = 1).

Figure 297. Example of encoder interface mode with tim_ti1fp1 polarity inverted

Figure 298 shows the timer counter value during a speed reversal, for various counting modes.

Figure 298. Quadrature encoder counting modes

The timer, when configured in Encoder Interface mode provides information on the sensor's current position. Dynamic information can be obtained (speed, acceleration, deceleration) by measuring the period between two encoder events using a second timer configured in capture mode. The output of the encoder which indicates the mechanical zero can be used for this purpose. Depending on the time between two events, the counter can also be read at regular times. This can be done by latching the counter value into a third input capture register if available (then the capture signal must be periodic and can be generated by another timer). When available, it is also possible to read its value through a DMA request.

The IUFREMAP bit in the TIMx_CR1 register forces a continuous copy of the update interrupt flag (UIF) into the timer counter register's bit 31 (TIMx_CNT[31]). This allows both the counter value and a potential roll-over condition signaled by the UIFCPY flag to be read in an atomic way. It eases the calculation of angular speed by avoiding race conditions caused, for instance, by a processing shared between a background task (counter reading) and an interrupt (update interrupt).

There is no latency between the UIF and UIFCPY flag assertions.

In 32-bit timer implementations, when the IUFREMAP bit is set, bit 31 of the counter is overwritten by the UIFCPY flag upon read access (the counter's most significant bit is only accessible in write mode).

Clock plus direction encoder mode

In addition to the quadrature encoder mode, the timer offers support for other types of encoders.

In the "clock plus direction" mode shown on Figure 299, the clock is provided on a single line, on tim_ti2, while the direction is forced using the tim_ti1 input.

This mode is enabled with the SMS[3:0] bitfield in the TIMx_SMCR register, as following:

• • 1010: x2 mode, the counter is updated on both rising and falling edges of the clock.
• • 1011: x1 mode, the counter is updated on a single clock edge, as per CC2P bit value: CC2P = 0 corresponds to rising edge sensitivity and CC2P = 1 corresponds to falling edge sensitivity.

The polarity of the direction signal on tim_ti1 is set with the CC1P bit: 0 corresponds to positive polarity (up-counting when tim_ti1 is high and down-counting when tim_ti1 is low) and CC1P = 1 corresponds to negative polarity (up-counting when tim_ti1 is low).

Figure 299. Direction plus clock encoder mode

Directional clock encoder mode

In the “directional clock” mode on Figure 300 , the clocks are provided on two lines, with a single one at once, depending on the direction, so as to have one up-counting clock line and one down-counting clock line.

This mode is enabled with the SMS[3:0] bitfield in the TIMx_SMCR register, as following:

• • 1100: x2 mode, the counter is updated on both rising and falling edges of any of the two clock lines. The CC1P and CC2P bits are coding for the clock idle state. CCxP = 0 corresponds to high-level idle state (refer to Figure 300 ) and CCxP = 1 corresponds to low-level idle state (refer to Figure 301 ).
• • 1101: x1 mode, the counter is updated on a single clock edge, as per CC1P and CC2P bit value. CCxP = 0 corresponds to falling edge sensitivity and high-level idle state (refer to Figure 300 ), CCxP = 1 corresponds to rising edge sensitivity and low-level idle state (refer to Figure 301 ).

Figure 300. Directional clock encoder mode (CC1P = CC2P = 0)

Figure 301. Directional clock encoder mode (CC1P = CC2P = 1)

Table 303 details how the directional clock mode operates, for any input transition.

Table 303. Counting direction versus encoder signals and polarity settings

Index input

The counter can be reset by an index signal coming from the encoder, indicating an absolute reference position. The index signal must be connected to the tim_etr_in input. It can be filtered using the digital input filter.

The index functionality is enabled with the IE bit in the TIMx_ECR register. The IE bit must be set only in encoder mode, when the SMS[3:0] bitfield has the following values: 0001, 0010, 011, 1010, 1011, 1100, 1101, 1110, 1111.

Available encoders are proposed with several options for index pulse conditioning, as per Figure 302:

• • Gated with A and B: the pulse width is 1/4 of one channel period, aligned with both A and B edges.
• • Gated with A (or gated with B): the pulse width is 1/2 of one channel period, aligned with the two edges on channel A (resp. channel B).
• • Ungated: the pulse width is up to one channel period, without any alignment to the edges.

Figure 302. Index gating options

The circuitry tolerates jitter on index signal, whatever the gating mode, as shown on Figure 303 .

In ungated mode, the signal must be strictly below two encoder periods. If the pulse width is greater or equal to two encoder period, the counter is reset multiple times.

Figure 303. Jittered Index signals

The timer supports the three gating options identically, without any specific programming needed. It is only necessary to define on which encoder state (for example channel A and channel B state combination) the index must be synchronized, using the IPOS[1:0] bitfield in the TIMx_ECR register.

The index detection event acts differently depending on counting direction to ensure symmetrical operation during speed reversal:

• • The counter is reset during up-counting (DIR bit = 0).
• • The counter is set to TIMx_ARR when down-counting.

This allows the index to be generated on the very same mechanical angular position whatever the counting direction. Figure 304 shows at which position is the index generated, for a simplistic example (an encoder providing four edges per mechanical rotation).

Figure 304. Index generation for IPOS[1:0] = 11

Figure 305 presents waveforms and corresponding values for IPOS[1:0] = 11. It shows that the instant at which the counter value is forced is automatically adjusted depending on the counting direction:

• • Counter set to 0 when encoder state is 11 (ChA = 1, ChB = 1), when up-counting (DIR bit = 0).
• • Counter set to TIMx_ARR when exiting the 11 state, when down-counting (DIR bit = 1).

An interrupt can be issued upon index detection event.

The arrows are indicating on which transition is the index event interrupt generated.

Figure 305. Counter reading with index gated on channel A (IPOS[1:0] = 11)

Figure 306 presents waveforms and corresponding values for the ungated mode. The arrows are indicating on which transition is the index event generated.

Figure 306. Counter reading with index ungated (IPOS[1:0] = 00)

Figure 307 shows how the gated on A & B mode is handled, for various pulse alignment scenarios. The arrows are indicating on which transition is the index event generated.

Figure 307. Counter reading with index gated on channel A and B

Figure 308 and Figure 309 detail the case where the subsequent index pulse may be narrower than one quarter of the encoder clock period.

Figure 308. Encoder mode behavior in case of narrow index pulse (IPOS[1:0] = 11)

Figure 309. Counter reset Narrow index pulse (closer view, ARR = 0x07)

Figure 310 shows how the index is managed in x1 and x2 modes.

Directional index sensitivity

The IDIR[1:0] bitfield in the TIMx_ECR register allows the index to be active only in a selected counting direction.

Figure 311 shows the relationship between index and counter reset events, depending on IDIR[1:0] value.

Special first index event management

The FIDX bit in the TIMx_ECR register allows the index to be taken only once, as shown on Figure 312 . Once the first index has arrived, any subsequent index is ignored. If needed, the circuitry can be rearmed by writing the FIDX bit to 0 and setting it again to 1.

Figure 312. Counter reset as function of FIDX bit setting

Index blanking

The index event can be blanked using the tim_ti3 or tim_ti4 inputs. During the blanking window, the index events are no longer resetting the counter, as shown on Figure 313 .

This mode is enabled using the IBLK[1:0] bitfield in the TIMx_ECR register, as following:

• • IBLK[1:0] = 00: Index signal always active.
• • IBLK[1:0] = 01: Index signal blanking on tim_ti3 input.
• • IBLK[1:0] = 10: Index signal blanking on tim_ti4 input.

Figure 313. Index blanking

Index management in nonquadrature mode

Figure 314 and Figure 315 detail how the index is managed in directional clock mode and clock plus direction mode, when the SMS[3:0] bitfield is equal to 1010, 1011, 1100, 1101.

For both of these modes, the index sensitivity is set with the IPOS[0] bit as following:

• • IPOS[0] = 0: Index is detected on clock low level.
• • IPOS[0] = 1: Index is detected on clock high level.

The IPOS[1] bit is not-significant.

Figure 314. Index behavior in clock + direction mode, IPOS[0] = 1

Figure 315. Index behavior in directional clock mode, IPOS[0] = 1

Encoder error management

For encoder configurations where two quadrature signals are available, it is possible to detect transition errors. The reading on the two inputs corresponds to a 2-bit gray code which can be represented as a state diagram, on Figure 316. A single bit is expected to change at once. An erroneous transition sets the TERRF interrupt flag in the TIMx_SR

status register. A transition error interrupt is generated if the TERRIE bit is set in the TIMx_DIER register.

Figure 316. State diagram for quadrature encoded signals

    graph LR
      00 <--> 01
      01 <--> 11
      11 <--> 10
      10 <--> 00
      00 -..-> 11
      10 -..-> 01
  

For encoder having an index signal, it is possible to detect abnormal operation resulting in an excess of pulses per revolution. An encoder with N pulses per revolution provides 4xN counts per revolution. The index signal resets the counter every 4xN clock periods.

If the counter value is incremented from TIMx_ARR to 0 or decremented from 0 to TIMx_ARR value without any index event, this is reported as an index position error.

The overflow threshold is programmed using the TIMx_ARR register. A 1000 lines encoder results in a counter value being between 0 and 3999 (in 4x reading mode). The overflow detection threshold must be programmed by setting TIMx_ARR = 3999 + 1 = 4000.

The error assertion is delayed to the transition 0 to 1 when in up-counting. This is to cope with narrow index pulses in gated A and B mode, as shown on Figure 317 .

Figure 317. Up-counting encoder error detection

In down-counting mode, the detection is conditioned by a preliminary transition from 1 to 0. This is to cope with narrow index pulses in gated A and B mode, as shown on Figure 318 , to avoid any false error detection in case the encoder dithers between TIMx_ARR and 0 immediately after the index detection.

Figure 318. Down-counting encode error detection

An index error sets the IERRF interrupt flag in the TIMx_SR status register. An index error interrupt is generated if the IERRIE bit is set in the TIMx_DIER register.

Functional encoder interrupts

The following interrupts are also available in encoder mode

• • Direction change: any change of the counting direction in encoder mode causes the DIR bit in the TIMx_CR1 register to toggle. The direction change sets the DIRF interrupt flag in the TIMx_SR status register. A direction change interrupt is generated if the DIRIE bit is set in the TIMx_DIER register.
• • Index event: the index event sets the IDXF interrupt flag in the TIMx_SR status register. An index interrupt is generated if the IDXIE bit is set in the TIMx_DIER register.

Slave mode selection preload for run-time encoder mode update

It can be necessary to switch from one encoder mode to another during run-time. This is typically done at high-speed to decrease the update interrupt rate, by switching from x4 to x2 to x1 mode, as shown on Figure 319 .

For this purpose, the SMS[3:0] bit can be preloaded. This is enabled by setting the SMSPE enable bit in the TIMx_SMCR register. The trigger for the transfer from SMS[3:0] preload to active value can be selected with the SMSPS bit in the TIMx_SMCR register.

• • SMSPS = 0: the transfer is triggered by the update event (UEV) occurring when the counter overflows when up-counting, and underflows when down-counting.
• • SMSPS = 1: the transfer is triggered by the index event.

Figure 319. Encoder mode change with preload transferred on update (SMSPS = 0)

Encoder clock output

The encoder mode operating principle is not perfectly suited for high-resolution velocity measurements, at low speed, as it requires a relatively long integration time to have a sufficient number of clock edges and a precise measurement.

At low speed, a better solution is to do an edge-to-edge clock period measurement. This can be achieved using a slave timer. The timer can output the encoder clock information on the tim_trgo output. The slave timer can then perform a period measurement and provide velocity information for each and every encoder clock edge.

This mode is enabled by setting the MMS[3:0] bitfield to 1000, in the TIMx_CR2 register. It is valid for the following SMS[3:0] values: 0001, 0010, 0011, 1010, 1011, 1100, 1101, 1110, 1111. Any other SMS[3:0] code is not allowed and may lead to unexpected behavior.

31.4.19 Direction bit output

It is possible to output a direction signal out of the timer, on the tim_oc3 and tim_oc4 output signals (copy of the DIR bit in the TIMx_CR1 register). This is achieved by setting the OC3M[3:0] or the OC4M[3:0] bitfield to 1011 in the TIMx_CCMR2 register.

This feature can be used for monitoring the counting direction (or rotation direction) in encoder mode, or to have a signal indicating the up/down phases in center-aligned PWM mode.

31.4.20 Clock drift measurement

It is possible to measure the drift between two clock sources using the directional clock encoder mode. This is useful for audio applications typically, when one needs to compute the drift between two streams.

To do so, a signal representing the rate of a first audio stream must be connected to tim_ti1 and a signal representing the rate of a second audio stream must be connected to tim_ti2 . The signals representing the audio rates are generally the SAIx_FS_A , SAIx_FS_B , SPIx_WS or spdifrx_frame_sync (this list of signals is provided as example and depends on the audio peripheral availability for a given product line, as detailed on the product datasheet).

In this case, the clocks are present on both tim_ti1 and tim2 simultaneously, as shown on Figure 320 , and the counter value indicates the drift.

Let's define \( F_{\text{tim\_ti1}} \) and \( F_{\text{tim\_ti2}} \) the frequencies of the signals on tim_ti1 and tim2 . The counter value will change as following:

• • If \( F_{\text{tim\_ti1}} > F_{\text{tim\_ti2}} \) the counter value increases.
• • If \( F_{\text{tim\_ti1}} < F_{\text{tim\_ti2}} \) the counter value decreases.
• • If \( F_{\text{tim\_ti1}} = F_{\text{tim\_ti2}} \) the counter value will dither between two consecutive values, from one clock edge to the other. If the two clocks are perfectly synchronized (clock edges occurring simultaneously on the two inputs), the counter value does not change (as shown on Figure 320 ).

Figure 320. Clock drift measure using directional clock mode

31.4.21 UIF bit remapping

The IUFREMAP bit in the TIMx_CR1 register forces a continuous copy of the update interrupt flag ( UIF ) into bit 31 of the timer counter register's bit 31 ( TIMx_CNT[31] ). This is used to atomically read both the counter value and a potential roll-over condition signaled by the UIFCPY flag. It eases the calculation of angular speed by avoiding race conditions caused, for instance, by a processing shared between a background task (counter reading) and an interrupt (update interrupt).

There is no latency between the UIF and UIFCPY flag assertions.

In 32-bit timer implementations, when the IUFREMAP bit is set, bit 31 of the counter is overwritten by the UIFCPY flag upon read access (the counter's most significant bit is only accessible in write mode).

31.4.22 Timer input XOR function

The TI1S bit in the TIMx_CR2 register, allows the input filter of channel 1 to be connected to the output of an XOR gate, combining the three input pins tim_ti1, tim_ti2 and tim_ti3.

The XOR output can be used with all the timer input functions such as trigger or input capture.

An example of this feature used to interface Hall sensors is given in Section 30.3.30: Interfacing with Hall sensors .

31.4.23 Timers and external trigger synchronization

The TIMx timers can be synchronized with an external trigger in several modes: Reset mode, Gated mode, Trigger mode, Reset + trigger and gated + reset modes.

Slave mode: Reset mode

The counter and its prescaler can be reinitialized in response to an event on a trigger input. Moreover, if the URS bit from the TIMx_CR1 register is low, an update event UEV is generated. Then all the preloaded registers (TIMx_ARR, TIMx_CCRx) are updated.

In the following example, the upcounter is cleared in response to a rising edge on tim_ti1 input:

1. 1. Configure the channel 1 to detect rising edges on tim_ti1. Configure the input filter duration (in this example, we do not need any filter, so we keep IC1F = 0000). The capture prescaler is not used for triggering, so it does not need to be configured. The CC1S bits select the input capture source only, CC1S = 01 in the TIMx_CCMR1 register. Write CC1P = 0 and CC1NP = 0 in TIMx_CCER register to validate the polarity (and detect rising edges only).
2. 2. Configure the timer in reset mode by writing SMS = 100 in TIMx_SMCR register. Select tim_ti1 as the input source by writing TS = 00101 in TIMx_SMCR register.
3. 3. Start the counter by writing CEN = 1 in the TIMx_CR1 register.

The counter starts counting on the internal clock, then behaves normally until tim_ti1 rising edge. When tim_ti1 rises, the counter is cleared and restarts from 0. In the meantime, the trigger flag is set (TIF bit in the TIMx_SR register) and an interrupt request, or a DMA request can be sent if enabled (depending on the TIE and TDE bits in TIMx_DIER register).

The following figure shows this behavior when the autoreload register TIMx_ARR = 0x36. The delay between the rising edge on tim_ti1 and the actual reset of the counter is due to the resynchronization circuit on tim_ti1 input.

Figure 321. Control circuit in reset mode

Slave mode: Gated mode

The counter can be enabled depending on the level of a selected input.

In the following example, the upcounter counts only when tim_ti1 input is low:

1. 1. Configure the channel 1 to detect low levels on tim_ti1. Configure the input filter duration (in this example, we do not need any filter, so we keep IC1F = 0000). The capture prescaler is not used for triggering, so it does not need to be configured. The CC1S bits select the input capture source only, CC1S = 01 in TIMx_CCMR1 register. Write CC1P = 1 and CC1NP = 0 in TIMx_CCER register to validate the polarity (and detect low level only).
2. 2. Configure the timer in gated mode by writing SMS = 101 in TIMx_SMCR register. Select tim_ti1 as the input source by writing TS = 00101 in TIMx_SMCR register.
3. 3. Enable the counter by writing CEN = 1 in the TIMx_CR1 register (in gated mode, the counter does not start if CEN = 0, whatever is the trigger input level).

The counter starts counting on the internal clock as long as tim_ti1 is low and stops as soon as tim_ti1 becomes high. The TIF flag in the TIMx_SR register is set both when the counter starts or stops.

The delay between the rising edge on tim_ti1 and the actual stop of the counter is due to the resynchronization circuit on tim_ti1 input.

Figure 322. Control circuit in gated mode

Note: The configuration “CCxP = CCxNP = 1” (detection of both rising and falling edges) does not have any effect in gated mode because gated mode acts on a level and not on an edge.

Slave mode: Trigger mode

The counter can start in response to an event on a selected input.

In the following example, the upcounter starts in response to a rising edge on tim_ti2 input:

1. 1. Configure the channel 2 to detect rising edges on tim_ti2. Configure the input filter duration (in this example, we do not need any filter, so we keep IC2F = 0000). The capture prescaler is not used for triggering, so it does not need to be configured. CC2S bits are selecting the input capture source only, CC2S = 01 in TIMx_CCMR1 register. Write CC2P = 1 and CC2NP = 0 in TIMx_CCER register to validate the polarity (and detect low level only).
2. 2. Configure the timer in trigger mode by writing SMS = 110 in TIMx_SMCR register. Select tim_ti2 as the input source by writing TS = 00110 in TIMx_SMCR register.

When a rising edge occurs on tim_ti2, the counter starts counting on the internal clock and the TIF flag is set.

The delay between the rising edge on tim_ti2 and the actual start of the counter is due to the resynchronization circuit on tim_ti2 input.

Figure 323. Control circuit in trigger mode

Slave mode selection preload for run-time encoder mode update

The SMS[3:0] bit can be preloaded. This is enabled by setting the SMSPE enable bit in the TIMx_SMCR register. The trigger for the transfer from SMS[3:0] preload to active value is the update event (UEV) occurring when the counter overflows.

Slave mode – combined reset + trigger mode

In this case, a rising edge of the selected trigger input (tim_trgi) reinitializes the counter, generates an update of the registers, and starts the counter.

This mode is used for one-pulse mode.

Slave mode – combined gated + reset mode

The counter clock is enabled when the trigger input (tim_trgi) is high. The counter stops and is reset as soon as the trigger becomes low. Both start and stop of the counter are controlled.

This mode is used to detect out-of-range PWM signal (duty cycle exceeding a maximum expected value).

Slave mode – external clock mode 2 + trigger mode

The external clock mode 2 can be used in addition to another slave mode (except external clock mode 1 and encoder mode). In this case, the tim_etr_in signal is used as external clock input, and another input can be selected as trigger input when operating in reset mode, gated mode, or trigger mode. It is recommended not to select tim_etr_in as tim_trgi through the TS bits of TIMx_SMCR register.

In the following example, the upcounter is incremented at each rising edge of the tim_etr_in signal as soon as a rising edge of tim_ti1 occurs:

1. 1. Configure the external trigger input circuit by programming the TIMx_SMCR register as follows:
   • – ETF = 0000: no filter.
   • – ETPS = 00: prescaler disabled.
   • – ETP = 0: detection of rising edges on tim_etr_in and ECE = 1 to enable the external clock mode 2.
2. 2. Configure the channel 1 as follows, to detect rising edges on TI:
   • – IC1F = 0000: no filter.
   • – The capture prescaler is not used for triggering and does not need to be configured.
   • – CC1S = 01 in TIMx_CCMR1 register to select only the input capture source.
   • – CC1P = 0 and CC1NP = 0 in TIMx_CCER register to validate the polarity (and detect rising edge only).
3. 3. Configure the timer in trigger mode by writing SMS = 110 in TIMx_SMCR register. Select tim_ti1 as the input source by writing TS = 00101 in TIMx_SMCR register.

A rising edge on tim_ti1 enables the counter and sets the TIF flag. The counter then counts on tim_etr_in rising edges.

The delay between the rising edge of the tim_etr_in signal and the actual reset of the counter is due to the resynchronization circuit on tim_etrp input.

Figure 324. Control circuit in external clock mode 2 + trigger mode

31.4.24 Timer synchronization

The TIMx timers are linked together internally for timer synchronization or chaining. When one timer is configured in Master mode, it can reset, start, stop, or clock the counter of another timer configured in Slave mode.

Figure 325 and Figure 326 show examples of master/slave timer connections.

Figure 325. Master/Slave timer example

Figure 326. Master/slave connection example with 1 channel only timers

Note: The timers with one channel only (see Figure 326) do not feature a master mode. However, the tim_oc1 output signal can serve as trigger for slave timer (see TIMx internal trigger connection table in Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals). The tim_oc1 signal pulse width must be programmed to be at least two clock cycles of the destination timer, to make sure the slave timer detects the trigger. For instance, if the destination timer tim_ker_ck clock is four times slower than the source timer, the OC1 pulse width must be eight clock cycles.

Using one timer as prescaler for another timer

For example, TIM_mstr can be configured to act as a prescaler for TIM_slv. Refer to Figure 325. To do this:

1. 1. Configure TIM_mstr in master mode so that it outputs a periodic trigger signal on each update event UEV. If MMS = 010 is written in the TIM_mstr_CR2 register, a rising edge is output on tim_trgo each time an update event is generated.
2. 2. To connect the tim_trgo output of TIM_mstr to TIM_slv, TIM_slv must be configured in slave mode using ITR2 as internal trigger. This is selected through the TS bits in the TIM_slv_SMCR register (writing TS = 00010).
3. 3. Then the slave mode controller must be put in external clock mode 1 (write SMS = 111 in the TIM_slv_SMCR register). This causes TIM_slv to be clocked by the rising edge of the periodic TIM_mstr trigger signal (which correspond to the TIM_mstr counter overflow).
4. 4. Finally both timers must be enabled by setting their respective CEN bits (TIMx_CR1 register).

Note: If tim_ocx is selected on TIM_mstr as the trigger output (MMS = 1xx), its rising edge is used to clock the counter of TIM_slv.

Using one timer to enable another timer

In this example, we control the enable of TIM_slv with the output compare 1 of TIM_mstr. Refer to Figure 325 for connections. TIM_slv counts on the divided internal clock only when tim_oc1ref of TIM_mstr is high. Both counter clock frequencies are divided by 3 by the prescaler compared to tim_ker_ck ( \( f_{\text{tim\_cnt\_ck}} = f_{\text{tim\_ker\_ck}}/3 \) ).

1. 1. Configure TIM_mstr master mode to send its output compare 1 reference (tim_oc1ref) signal as trigger output (MMS = 100 in the TIM_mstr_CR2 register).
2. 2. Configure the TIM_mstr tim_oc1ref waveform (TIM_mstr_CCMR1 register).
3. 3. Configure TIM_slv to get the input trigger from TIM_mstr (TS = 00010 in the TIM_slv_SMCR register).
4. 4. Configure TIM_slv in gated mode (SMS = 101 in TIM_slv_SMCR register).
5. 5. Enable TIM_slv by writing 1 in the CEN bit (TIM_slv_CR1 register).
6. 6. Start TIM_mstr by writing 1 in the CEN bit (TIM_mstr_CR1 register).

Note: The slave timer counter clock is not synchronized with the master timer counter clock, this mode only affects the TIM_slv counter enable signal.

Figure 327. Gating TIM_slv with tim_oc1ref of TIM_mstr

In the example in Figure 327, the TIM_slv counter and prescaler are not initialized before being started. So they start counting from their current value. It is possible to start from a given value by resetting both timers before starting TIM_mstr. Then any value can be written in the timer counters. The timers can easily be reset by software using the UG bit in the TIMx_EGR registers.

In the next example (refer to Figure 328 ), we synchronize TIM_mstr and TIM_slv. TIM_mstr is the master and starts from 0. TIM_slv is the slave and starts from 0xE7. The prescaler ratio is the same for both timers. TIM_slv stops when TIM_mstr is disabled by writing 0 to the CEN bit in the TIM_mstr_CR1 register:

1. 1. Configure TIM_mstr master mode to send its output compare 1 reference (tim_oc1ref) signal as trigger output (MMS = 100 in the TIM_mstr_CR2 register).
2. 2. Configure the TIM_mstr tim_oc1ref waveform (TIM_mstr_CCMR1 register).
3. 3. Configure TIM_slv to get the input trigger from TIM_mstr (TS = 00010 in the TIM_slv_SMCR register).
4. 4. Configure TIM_slv in gated mode (SMS = 101 in TIM_slv_SMCR register).
5. 5. Reset TIM_mstr by writing 1 in UG bit (TIM_mstr_EGR register).
6. 6. Reset TIM_slv by writing 1 in UG bit (TIM_slv_EGR register).
7. 7. Initialize TIM_slv to 0xE7 by writing 0xE7 in the TIM_slv counter (TIM_slv_CNT).
8. 8. Enable TIM_slv by writing 1 in the CEN bit (TIM_slv_CR1 register).
9. 9. Start TIM_mstr by writing 1 in the CEN bit (TIM_mstr_CR1 register).
10. 10. Stop TIM_mstr by writing 0 in the CEN bit (TIM_mstr_CR1 register).

Figure 328. Gating TIM_slv with Enable of TIM_mstr

Using one timer to start another timer

In this example, we set the enable of TIM_slv with the update event of TIM_mstr. Refer to Figure 325 for connections. TIM_slv starts counting from its current value (which can be nonzero) on the divided internal clock as soon as the update event is generated by TIM_mstr. When TIM_slv receives the trigger signal its CEN bit is automatically set and the counter counts until we write 0 to the CEN bit in the TIM_slv_CR1 register. Both counter clock frequencies are divided by 3 by the prescaler compared to tim_ker_ck ( \( f_{\text{tim\_cnt\_ck}} = f_{\text{tim\_ker\_ck}}/3 \) ).

1. 1. Configure TIM_mstr master mode to send its update event (UEV) as trigger output (MMS = 010 in the TIM_mstr_CR2 register).
2. 2. Configure the TIM_mstr period (TIM_mstr_ARR registers).
3. 3. Configure TIM_slv to get the input trigger from TIM_mstr (TS = 00010 in the TIM_slv_SMCR register).
4. 4. Configure TIM_slv in trigger mode (SMS = 110 in TIM_slv_SMCR register).
5. 5. Start TIM_mstr by writing 1 in the CEN bit (TIM_mstr_CR1 register).

Figure 329. Triggering TIM_slv with update of TIM_mstr

As in the previous example, both counters can be initialized before starting counting.

Figure 330 shows the behavior with the same configuration as in Figure 329 but in trigger mode (SMS = 110 in the TIM_slv_SMCR register) instead of gated mode.

Figure 330. Triggering TIM_slv with Enable of TIM_mstr

Starting two timers synchronously in response to an external trigger

In this example, we set the enable of TIM_mstr when its tim_ti1 input rises, and the enable of TIM_slv with the enable of TIM_mstr. Refer to Figure 325 for connections. To ensure the counters are aligned, TIM_mstr must be configured in Master/Slave mode (slave with respect to tim_ti1, master with respect to TIM_slv):

1. 1. Configure TIM_mstr master mode to send its enable as trigger output (MMS = 001 in the TIM_mstr_CR2 register).
2. 2. Configure TIM_mstr slave mode to get the input trigger from tim_ti1 (TS = 00100 in the TIM_mstr_SMCR register).
3. 3. Configure TIM_mstr in trigger mode (SMS = 110 in the TIM_mstr_SMCR register).
4. 4. Configure the TIM_mstr in Master/Slave mode by writing MSM = 1 (TIM_mstr_SMCR register).
5. 5. Configure TIM_slv to get the input trigger from TIM_mstr (TS = 00000 in the TIM_slv_SMCR register).
6. 6. Configure TIM_slv in trigger mode (SMS = 110 in the TIM_slv_SMCR register).

When a rising edge occurs on tim_ti1 (TIM_mstr), both counters start counting synchronously on the internal clock and both TIF flags are set.

Note: In this example both timers are initialized before starting (by setting their respective UG bits). Both counters starts from 0, but an offset can easily be inserted between them by writing any of the counter registers (TIMx_CNT). One can see that the master/slave mode inserts a delay between CNT_EN and CK_PSC on TIM_mstr.

Figure 331. Triggering TIM_mstr and TIM_slv with TIM_mstr tim_ti1 input

Note: The clock of the slave peripherals (such as timer, ADC) receiving the tim_trgo signal must be enabled prior to receive events from the master timer, and the clock frequency (prescaler) must not be changed on-the-fly while triggers are received from the master timer.

31.4.25 ADC triggers

The timer can generate an ADC triggering event with various internal signals, such as reset, enable or compare events.

Note: The clock of the slave peripherals (such as timer, ADC) receiving the tim_trgo signal must be enabled prior to receive events from the master timer, and the clock frequency (prescaler) must not be changed on-the-fly while triggers are received from the master timer.

31.4.26 ADC synchronization

The timer operation can be synchronized to the ADC clock to trigger jitter-free ADC sampling. This function is enabled using the ADSYNC bit in the TIMx_CR2 register.

This feature is useful when the timers and the ADCs are operating with semisynchronous clocks (clocks derived from a same source with integer ratio tim_ker_ck/adc_ker_ck ), for instance adc_ker_ck = 75 MHz and tim_ker_ck = 150 MHz or 300 MHz.

ADSYNC must also be set when both peripherals are operating at the same frequency from the same clock source, when jitter-free operation is needed.

ADSYNC must not be set and jitter-free operation is not supported in the following cases:

• • When the clock ratio is not an integer (for example adc_ker_ck = 75 MHz and tim_ker_ck = 100 MHz): in this case, the sampling point jitter due to the timer to ADC signal resynchronization is 1 adc_ker_ck period maximum.
• • When the ADC is operating in asynchronous mode ( adc_ker_ck uncorrelated with tim_ker_ck ): in this case, the sampling point jitter due to the timer to ADC signal resynchronization is 1 adc_ker_ck period maximum.

When ADSYNC = 1, the timer operation is slightly changed: the counter enable and counter reset events are aligned to the adc_ker_ck ADC clock, to avoid any phase shift due to clocks enable in the RCC.

Jitter-free operation is guaranteed only when one of the two requirements below is met (depending on the selected trigger source):

1. 1. The counter period must be a multiple of the ADC clock period.

1. 2. The compare value must be a multiple of the ADC clock period.

Note: If none of the two above requirements is met, the trigger is still generated, but the latency is not constant and varies with the timer and ADC clocks phase shift.

Programming guidelines

The ADC synchronization feature must not be modified during run-time, once the counter is enabled and once the ADC has been configured for receiving triggers from the timer.

It is mandatory to follow the procedure below to use the ADC synchronization:

1. 1. Enable the destination ADC clock.
2. 2. Configure the timer and set the ADSYNC bit.
3. 3. Configure the ADC and enable it (using ADSTART and/or JADSTART bits).
4. 4. Start the timer (with the CEN counter enable bit).

31.4.27 DMA burst mode

The TIMx timers have the capability to generate multiple DMA requests upon a single event. The main purpose is to be able to reprogram part of the timer multiple times without software overhead, but it can also be used to read several registers in a row, at regular intervals.

The DMA controller destination is unique and must point to the virtual register TIMx_DMAR. On a given timer event, the timer launches a sequence of DMA requests (burst). Each write into the TIMx_DMAR register is actually redirected to one of the timer registers.

The DBL[4:0] bits in the TIMx_DCR register set the DMA burst length. The timer recognizes a burst transfer when a read or a write access is done to the TIMx_DMAR address), i.e. the number of transfers (either in half-words or in bytes).

The DBA[4:0] bits in the TIMx_DCR registers define the DMA base address for DMA transfers (when read/write accesses are done through the TIMx_DMAR address). DBA is defined as an offset starting from the address of the TIMx_CR1 register:

Example:

00000: TIMx_CR1

00001: TIMx_CR2

00010: TIMx_SMCR

The DBSS[3:0] bits in the TIMx_DCR register defines the interrupt source that triggers the DMA burst transfers (see Section 31.5.29: TIMx DMA control register (TIMx_DCR)(x = 2 to 4) for details).

As an example, the timer DMA burst feature is used to update the contents of the CCRx registers (x = 2, 3, 4) upon an update event, with the DMA transferring half words into the CCRx registers.

This is done in the following steps:

1. 1. Configure the corresponding DMA channel as follows:
   • – DMA channel peripheral address is the DMAR register address.
   • – DMA channel memory address is the address of the buffer in the RAM containing the data to be transferred by DMA into CCRx registers.
   • – Number of data to transfer = 3 (See note below).
   • – Circular mode disabled.
2. 2. Configure the DCR register by configuring the DBA and DBL bitfields as follows: DBL = 3 transfers, DBA = 0xE and DBSS = 1.
3. 3. Enable the TIMx update DMA request (set the UDE bit in the DIER register).
4. 4. Enable TIMx.
5. 5. Enable the DMA channel.

This example is for the case where every CCRx register has to be updated once. If every CCRx register is to be updated twice for example, the number of data to transfer must be 6. Let's take the example of a buffer in the RAM containing data1, data2, data3, data4, data5, and data6. The data is transferred to the CCRx registers as follows: on the first update DMA request, data1 is transferred to CCR2, data2 is transferred to CCR3, data3 is transferred to CCR4 and on the second update DMA request, data4 is transferred to CCR2, data5 is transferred to CCR3, and data6 is transferred to CCR4.

Note: A null value can be written to the reserved registers.

31.4.28 TIM2/TIM3/TIM4 DMA requests

The TIM2/TIM3/TIM4 can generate a DMA requests, as shown in Table 304 .

Table 304. DMA request

Note: Some timer's DMA requests may not be connected to the DMA controller. Refer to the DMA section(s) for more details.

31.4.29 Debug mode

When the microcontroller enters debug mode (core core halted), the TIMx counter can either continue to work normally or stops.

The behavior in debug mode can be programmed with a dedicated configuration bit per timer in the Debug support (DBG) module.

For more details, refer to section Debug support (DBG).

31.4.30 TIM2/TIM3/TIM4 low-power modes

Table 305. Effect of low-power modes on TIM2/TIM3/TIM4

31.4.31 TIM2/TIM3/TIM4 interrupts

The TIM2/TIM3/TIM4 can generate multiple interrupts, as shown in Table 306 .

Table 306. Interrupt requests

31.5 TIM2/TIM3/TIM4 registers

Refer to Section 1.2 for a list of abbreviations used in register descriptions.

The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

31.5.1 TIMx control register 1 (TIMx_CR1)(x = 2 to 4)

Address offset: 0x000

Reset value: 0x0000

Bits 15:13 Reserved, must be kept at reset value.

Bit 12 DITHEN : Dithering Enable
0: Dithering disabled
1: Dithering enabled

Note: The DITHEN bit can only be modified when CEN bit is reset.

Bit 11 UIFREMAP : UIF status bit remapping
0: No remapping. UIF status bit is not copied to TIMx_CNT register bit 31.
1: Remapping enabled. UIF status bit is copied to TIMx_CNT register bit 31.

Bit 10 Reserved, must be kept at reset value.

Bits 9:8 CKD[1:0] : Clock division

This bitfield indicates the division ratio between the timer clock (tim_ker_ck) frequency and sampling clock used by the digital filters (tim_etr_in, tim_tix),
00: \( t_{DTS} = t_{tim\_ker\_ck} \)
01: \( t_{DTS} = 2 \times t_{tim\_ker\_ck} \)
10: \( t_{DTS} = 4 \times t_{tim\_ker\_ck} \)
11: Reserved

Bit 7 ARPE : Autoreload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered

Bits 6:5 CMS[1:0] : Center-aligned mode selection

00: Edge-aligned mode. The counter counts up or down depending on the direction bit (DIR).
01: Center-aligned mode 1. The counter counts up and down alternatively. Output compare interrupt flags of channels configured in output (CCxS = 00 in TIMx_CCMRx register) are set only when the counter is counting down.
10: Center-aligned mode 2. The counter counts up and down alternatively. Output compare interrupt flags of channels configured in output (CCxS = 00 in TIMx_CCMRx register) are set only when the counter is counting up.
11: Center-aligned mode 3. The counter counts up and down alternatively. Output compare interrupt flags of channels configured in output (CCxS = 00 in TIMx_CCMRx register) are set both when the counter is counting up or down.

Note: It is not allowed to switch from edge-aligned mode to center-aligned mode as long as the counter is enabled (CEN = 1)

Bit 4 DIR : Direction

• 0: Counter used as upcounter
• 1: Counter used as downcounter

Note: This bit is read only when the timer is configured in Center-aligned mode or Encoder mode.

Bit 3 OPM : One-pulse mode

• 0: Counter is not stopped at update event
• 1: Counter stops counting at the next update event (clearing the bit CEN)

Bit 2 URS : Update request source

This bit is set and cleared by software to select the UEV event sources.

• 0: Any of the following events generate an update interrupt or DMA request if enabled.

These events can be:

• - Counter overflow/underflow
• - Setting the UG bit
• - Update generation through the slave mode controller

• 1: Only counter overflow/underflow generates an update interrupt or DMA request if enabled.

Bit 1 UDIS : Update disable

This bit is set and cleared by software to enable/disable UEV event generation.

• 0: UEV enabled. The Update (UEV) event is generated by one of the following events:

• - Counter overflow/underflow
• - Setting the UG bit
• - Update generation through the slave mode controller

Buffered registers are then loaded with their preload values.

• 1: UEV disabled. The Update event is not generated, shadow registers keep their value (ARR, PSC, CCRx). However the counter and the prescaler are reinitialized if the UG bit is set or if a hardware reset is received from the slave mode controller.

Bit 0 CEN : Counter enable

• 0: Counter disabled
• 1: Counter enabled

Note: External clock, gated mode and encoder mode can work only if the CEN bit has been previously set by software. However trigger mode can set the CEN bit automatically by hardware.

CEN is cleared automatically in one-pulse mode, when an update event occurs.

31.5.2 TIMx control register 2 (TIMx_CR2)(x = 2 to 4)

Address offset: 0x004

Reset value: 0x0000 0000

Bits 31:29 Reserved, must be kept at reset value.

Bit 28 ADSYNC : ADC synchronization

0: The timer operates independently from the ADC

1: The timer operation is synchronized with the ADC clock to provide jitter-free sampling point. This mode can be enabled only with specific ADC / timer clock relationship. Refer to Section 31.4.26 for requirements.

The ADSYNC must not modified when the counter is enabled (CEN bit is set).

Bits 27:26 Reserved, must be kept at reset value.

Bits 24:8 Reserved, must be kept at reset value.

Bit 7 TI1S : tim_ti1 selection

0: The tim_ti1_in[15:0] multiplexer output is to tim_ti1 input

1: The tim_ti1_in[15:0], tim_ti2_in[15:0] and tim_ti3_in[15:0] multiplexers outputs are XORed and connected to the tim_ti1 input. See also Section 30.3.30: Interfacing with Hall sensors .

Bits 25, 6, 5, 4 MMS[3:0] : Master mode selection

These bits are used to select the information to be sent in master mode to slave timers for synchronization (tim_trgo). The combination is as follows:

0000: Reset - the UG bit from the TIMx_EGR register is used as trigger output (tim_trgo). If the reset is generated by the trigger input (slave mode controller configured in reset mode) then the signal on tim_trgo is delayed compared to the actual reset.

0001: Enable - the Counter enable signal, CNT_EN, is used as trigger output (tim_trgo). It is useful to start several timers at the same time or to control a window in which a slave timer is enabled. The Counter Enable signal is generated by a logic AND between CEN control bit and the trigger input when configured in gated mode.

When the Counter Enable signal is controlled by the trigger input, there is a delay on tim_trgo, except if the master/slave mode is selected (see the MSM bit description in TIMx_SMCR register).

0010: Update - The update event is selected as trigger output (tim_trgo). For instance a master timer can then be used as a prescaler for a slave timer.

0011: Compare Pulse - The trigger output send a positive pulse when the CC1IF flag is to be set (even if it was already high), as soon as a capture or a compare match occurred (tim_trgo).

0100: Compare - tim_oc1refc signal is used as trigger output (tim_trgo)

0101: Compare - tim_oc2refc signal is used as trigger output (tim_trgo)

0110: Compare - tim_oc3refc signal is used as trigger output (tim_trgo)

0111: Compare - tim_oc4refc signal is used as trigger output (tim_trgo)

1000: Encoder clock output - The encoder clock signal is used as trigger output (tim_trgo). This code is valid for the following SMS[3:0] values: 0001, 0010, 0011, 1010, 1011, 1100, 1101, 1110, 1111. Any other SMS[3:0] code is not allowed and may lead to unexpected behavior.

Others: Reserved

Note: The clock of the slave timer or ADC must be enabled prior to receive events from the master timer, and must not be changed on-the-fly while triggers are received from the master timer.

Bit 3 CCDS : Capture/compare DMA selection

0: CCx DMA request sent when CCx event occurs

1: CCx DMA requests sent when update event occurs

Bits 2:0 Reserved, must be kept at reset value.

31.5.3 TIMx slave mode control register (TIMx_SMCR)(x = 2 to 4)

Address offset: 0x008

Reset value: 0x0000 0000

Bits 31:26 Reserved, must be kept at reset value.

Bit 25 SMSPS : SMS preload source

This bit selects whether the events that triggers the SMS[3:0] bitfield transfer from preload to active

0: The transfer is triggered by the Timer's Update event

1: The transfer is triggered by the Index event

Bit 24 SMSPE : SMS preload enable

This bit selects whether the SMS[3:0] bitfield is preloaded

0: SMS[3:0] bitfield is not preloaded

1: SMS[3:0] preload is enabled

Bits 23:22 Reserved, must be kept at reset value.

Bits 19:17 Reserved, must be kept at reset value.

Bit 15 ETP : External trigger polarity

This bit selects whether tim_etr_in or tim_etr_in is used for trigger operations

0: tim_etr_in is non-inverted, active at high level or rising edge

1: tim_etr_in is inverted, active at low level or falling edge

Bit 14 ECE : External clock enable

This bit enables External clock mode 2.

0: External clock mode 2 disabled

1: External clock mode 2 enabled. The counter is clocked by any active edge on the tim_etrf signal.

Note: Setting the ECE bit has the same effect as selecting external clock mode 1 with tim_trgi connected to tim_etrf (SMS = 111 and TS = 00111).

It is possible to simultaneously use external clock mode 2 with the following slave modes: reset mode, gated mode and trigger mode. Nevertheless, tim_trgi must not be connected to tim_etrf in this case (TS bits must not be 00111).

If external clock mode 1 and external clock mode 2 are enabled at the same time, the external clock input is tim_etrf .

Bits 13:12 ETPS[1:0] : External trigger prescaler

External trigger signal tim_etrp frequency must be at most 1/4 of tim_ker_ck frequency. A prescaler can be enabled to reduce tim_etrp frequency. It is useful when inputting fast external clocks on tim_etr_in .

00: Prescaler OFF

01: tim_etrp frequency divided by 2

10: tim_etrp frequency divided by 4

11: tim_etrp frequency divided by 8

This bitfield then defines the frequency used to sample tim_etrp signal and the length of the digital filter applied to tim_etrp. The digital filter is made of an event counter in which N consecutive events are needed to validate a transition on the output:

0000: No filter, sampling is done at \( f_{DTS} \)

0001: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 2

0010: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 4

0011: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 8

0100: \( f_{SAMPLING} = f_{DTS}/2 \) , N = 6

0101: \( f_{SAMPLING} = f_{DTS}/2 \) , N = 8

0110: \( f_{SAMPLING} = f_{DTS}/4 \) , N = 6

0111: \( f_{SAMPLING} = f_{DTS}/4 \) , N = 8

1000: \( f_{SAMPLING} = f_{DTS}/8 \) , N = 6

1001: \( f_{SAMPLING} = f_{DTS}/8 \) , N = 8

1010: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 5

1011: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 6

1100: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 8

1101: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 5

1110: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 6

1111: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 8

0: No action

1: The effect of an event on the trigger input (tim_trgi) is delayed to allow a perfect synchronization between the current timer and its slaves (through tim_trgo). It is useful if we want to synchronize several timers on a single external event.

Bits 21, 20, 6, 5, 4 TS[4:0] : Trigger selection

This bitfield selects the trigger input to be used to synchronize the counter.

• 00000: Internal trigger 0 (tim_itr0)
• 00001: Internal trigger 1 (tim_itr1)
• 00010: Internal trigger 2 (tim_itr2)
• 00011: Internal trigger 3 (tim_itr3)
• 00100: tim_ti1 edge detector (tim_ti1f_ed)
• 00101: Filtered timer input 1 (tim_ti1fp1)
• 00110: Filtered timer input 2 (tim_ti2fp2)
• 00111: External trigger input (tim_etrf)
• 01000: Internal trigger 4 (tim_itr4)
• 01001: Internal trigger 5 (tim_itr5)
• 01010: Internal trigger 6 (tim_itr6)
• 01011: Internal trigger 7 (tim_itr7)
• 01100: Internal trigger 8 (tim_itr8)
• 01101: Internal trigger 9 (tim_itr9)
• 01110: Internal trigger 10 (tim_itr10)
• 01111: Internal trigger 11 (tim_itr11)
• 10000: Internal trigger 12 (tim_itr12)
• 10001: Internal trigger 13 (tim_itr13)
• 10010: Internal trigger 14 (tim_itr14)
• 10011: Internal trigger 15 (tim_itr15)

Others: Reserved

See Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation details.

Note: These bits must be changed only when they are not used (for example when SMS = 000) to avoid wrong edge detections at the transition.

Bit 3 OCCS : OCREF clear selection

This bit is used to select the OCREF clear source

• 0: tim_ocref_clr_int is connected to the tim_ocref_clr input

• 1: tim_ocref_clr_int is connected to tim_etrf

Note: If the OCREF clear selection feature is not supported, this bit is reserved and forced by hardware to 0. Section 31.3: TIM2/TIM3/TIM4 implementation .

Bits 16, 2, 1, 0 SMS[3:0] : Slave mode selection

When external signals are selected the active edge of the trigger signal (tim_trgi) is linked to the polarity selected on the external input (refer to ETP bit in TIMx_SMCR for tim_etr_in and CCxP/CCxNP bits in TIMx_CCER register for tim_ti1fp1 and tim_ti2fp2).

0000: Slave mode disabled - if CEN = 1 then the prescaler is clocked directly by the internal clock.

0001: Encoder mode 1 - Counter counts up/down on tim_ti1fp1 edge depending on tim_ti2fp2 level.

0010: Encoder mode 2 - Counter counts up/down on tim_ti2fp2 edge depending on tim_ti1fp1 level.

0011: Encoder mode 3 - Counter counts up/down on both tim_ti1fp1 and tim_ti2fp2 edges depending on the level of the other input.

0100: Reset mode - Rising edge of the selected trigger input (tim_trgi) reinitializes the counter and generates an update of the registers.

0101: Gated mode - The counter clock is enabled when the trigger input (tim_trgi) is high. The counter stops (but is not reset) as soon as the trigger becomes low. Both start and stop of the counter are controlled.

0110: Trigger mode - The counter starts at a rising edge of the trigger tim_trgi (but it is not reset). Only the start of the counter is controlled.

0111: External clock mode 1 - Rising edges of the selected trigger (tim_trgi) clock the counter.

1000: Combined reset + trigger mode - Rising edge of the selected trigger input (tim_trgi) reinitializes the counter, generates an update of the registers and starts the counter.

1001: Combined gated + reset mode - The counter clock is enabled when the trigger input (tim_trgi) is high. The counter stops and is reset) as soon as the trigger becomes low. Both start and stop of the counter are controlled.

1010: Encoder mode: Clock plus direction, x2 mode.

1011: Encoder mode: Clock plus direction, x1 mode, tim_ti2fp2 edge sensitivity is set by CC2P.

1100: Encoder mode: Directional clock, x2 mode.

1101: Encoder mode: Directional clock, x1 mode, tim_ti1fp1 and tim_ti2fp2 edge sensitivity is set by CC1P and CC2P.

1110: Quadrature encoder mode: x1 mode, counting on tim_ti1fp1 edges only, edge sensitivity is set by CC1P.

1111: Quadrature encoder mode: x1 mode, counting on tim_ti2fp2 edges only, edge sensitivity is set by CC2P.

Note: The gated mode must not be used if tim_ti1f_ed is selected as the trigger input (TS = 00100). Indeed, tim_ti1f_ed outputs 1 pulse for each transition on tim_ti1f, whereas the gated mode checks the level of the trigger signal.

Note: The clock of the slave peripherals (such as timer, ADC) receiving the tim_trgo signal must be enabled prior to receive events from the master timer, and the clock frequency (prescaler) must not be changed on-the-fly while triggers are received from the master timer.

31.5.4 TIMx DMA/Interrupt enable register (TIMx_DIER)(x = 2 to 4)

Address offset: 0x00C

Reset value: 0x0000 0000

Bits 31:24 Reserved, must be kept at reset value.

Bit 23 TERRIE : Transition error interrupt enable

0: Transition error interrupt disabled

1: Transition error interrupt enabled

Bit 22 IERRIE : Index error interrupt enable

0: Index error interrupt disabled

1: Index error interrupt enabled

Bit 21 DIRIE : Direction change interrupt enable

0: Direction change interrupt disabled

1: Direction change interrupt enabled

Bit 20 IDXIE : Index interrupt enable

0: Index interrupt disabled

1: Index interrupt enabled

Bits 19:15 Reserved, must be kept at reset value.

Bit 14 TDE : Trigger DMA request enable

0: Trigger DMA request disabled.

1: Trigger DMA request enabled.

Bit 13 Reserved, must be kept at reset value.

Bit 12 CC4DE : Capture/Compare 4 DMA request enable

0: CC4 DMA request disabled.

1: CC4 DMA request enabled.

Bit 11 CC3DE : Capture/Compare 3 DMA request enable

0: CC3 DMA request disabled.

1: CC3 DMA request enabled.

Bit 10 CC2DE : Capture/Compare 2 DMA request enable

0: CC2 DMA request disabled.

1: CC2 DMA request enabled.

Bit 9 CC1DE : Capture/Compare 1 DMA request enable

0: CC1 DMA request disabled.

1: CC1 DMA request enabled.

Bit 8 UDE : Update DMA request enable

0: Update DMA request disabled.

1: Update DMA request enabled.

1. Bit 7 Reserved, must be kept at reset value.
2. Bit 6 TIE : Trigger interrupt enable
   0: Trigger interrupt disabled.
   1: Trigger interrupt enabled.
3. Bit 5 Reserved, must be kept at reset value.
4. Bit 4 CC4IE : Capture/Compare 4 interrupt enable
   0: CC4 interrupt disabled.
   1: CC4 interrupt enabled.
5. Bit 3 CC3IE : Capture/Compare 3 interrupt enable
   0: CC3 interrupt disabled.
   1: CC3 interrupt enabled.
6. Bit 2 CC2IE : Capture/Compare 2 interrupt enable
   0: CC2 interrupt disabled.
   1: CC2 interrupt enabled.
7. Bit 1 CC1IE : Capture/Compare 1 interrupt enable
   0: CC1 interrupt disabled.
   1: CC1 interrupt enabled.
8. Bit 0 UIE : Update interrupt enable
   0: Update interrupt disabled.
   1: Update interrupt enabled.

31.5.5 TIMx status register (TIMx_SR)(x = 2 to 4)

Address offset: 0x010

Reset value: 0x0000 0000

Bits 31:24 Reserved, must be kept at reset value.

Bit 23 TERRF : Transition error interrupt flag

This flag is set by hardware when a transition error is detected in encoder mode. It is cleared by software by writing it to 0.

0: No encoder transition error has been detected.

1: An encoder transition error has been detected

Bit 22 IERRF : Index error interrupt flag

This flag is set by hardware when an index error is detected. It is cleared by software by writing it to 0.

0: No index error has been detected.

1: An index error has been detected

Bit 21 DIRF : Direction change interrupt flag

This flag is set by hardware when the direction changes in encoder mode (DIR bit value in TIMx_CR is changing). It is cleared by software by writing it to 0.

0: No direction change

1: Direction change

Bit 20 IDXF : Index interrupt flag

This flag is set by hardware when an index event is detected. It is cleared by software by writing it to 0.

0: No index event occurred.

1: An index event has occurred

Bits 19:13 Reserved, must be kept at reset value.

Bit 12 CC4OF : Capture/Compare 4 overcapture flag

refer to CC1OF description

Bit 11 CC3OF : Capture/Compare 3 overcapture flag

refer to CC1OF description

Bit 10 CC2OF : Capture/compare 2 overcapture flag

refer to CC1OF description

Bit 9 CC1OF : Capture/Compare 1 overcapture flag

This flag is set by hardware only when the corresponding channel is configured in input capture mode. It is cleared by software by writing it to 0.

0: No overcapture has been detected.

1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was already set

Bits 8:7 Reserved, must be kept at reset value.

Bit 6 TIF : Trigger interrupt flag

This flag is set by hardware on the TRG trigger event (active edge detected on tim_trgi input) when the slave mode controller is enabled in all modes but gated mode. It is set when the counter starts or stops when gated mode is selected. It is cleared by software.

0: No trigger event occurred.

1: Trigger interrupt pending.

Bit 5 Reserved, must be kept at reset value.

Bit 4 CC4IF : Capture/Compare 4 interrupt flag

Refer to CC1IF description

Bit 3 CC3IF : Capture/Compare 3 interrupt flag

Refer to CC1IF description

Bit 2 CC2IF : Capture/Compare 2 interrupt flag

Refer to CC1IF description

Bit 1 CC1IF : Capture/compare 1 interrupt flag

This flag is set by hardware. It is cleared by software (input capture or output compare mode) or by reading the TIMx_CCR1 register (input capture mode only).

0: No compare match / No input capture occurred

1: A compare match or an input capture occurred

If channel CC1 is configured as output: this flag is set when the content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register. When the content of TIMx_CCR1 is greater than the content of TIMx_ARR, the CC1IF bit goes high on the counter overflow (in up-counting and up/down-counting modes) or underflow (in down-counting mode). There are three possible options for flag setting in center-aligned mode, refer to the CMS bits in the TIMx_CR1 register for the full description.

If channel CC1 is configured as input: this bit is set when counter value has been captured in TIMx_CCR1 register (an edge has been detected on IC1, as per the edge sensitivity defined with the CC1P and CC1NP bits setting, in TIMx_CCER).

Bit 0 UIF : Update interrupt flag

This bit is set by hardware on an update event. It is cleared by software.

0: No update occurred

1: Update interrupt pending. This bit is set by hardware when the registers are updated:

At overflow or underflow and if UDIS = 0 in the TIMx_CR1 register.

When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if URS = 0 and UDIS = 0 in the TIMx_CR1 register.

When CNT is reinitialized by a trigger event (refer to the synchro control register description), if URS = 0 and UDIS = 0 in the TIMx_CR1 register.

31.5.6 TIMx event generation register (TIMx_EGR)(x = 2 to 4)

Address offset: 0x014

Reset value: 0x0000

Bits 15:7 Reserved, must be kept at reset value.

Bit 6 TG : Trigger generation

This bit is set by software in order to generate an event, it is automatically cleared by hardware.

0: No action

1: The TIF flag is set in TIMx_SR register. Related interrupt or DMA transfer can occur if enabled.

Bit 5 Reserved, must be kept at reset value.

Bit 4 CC4G : Capture/compare 4 generation

Refer to CC1G description

Bit 3 CC3G : Capture/compare 3 generation

Refer to CC1G description

Bit 2 CC2G : Capture/compare 2 generation

Refer to CC1G description

Bit 1 CC1G : Capture/compare 1 generation

This bit is set by software in order to generate an event, it is automatically cleared by hardware.

0: No action

1: A capture/compare event is generated on channel 1:

If channel CC1 is configured as output:

CC1IF flag is set, Corresponding interrupt or DMA request is sent if enabled.

If channel CC1 is configured as input:

The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set, the corresponding interrupt or DMA request is sent if enabled. The CC1OF flag is set if the CC1IF flag was already high.

Bit 0 UG : Update generation

This bit can be set by software, it is automatically cleared by hardware.

0: No action

1: Re-initialize the counter and generates an update of the registers. Note that the prescaler counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared if the center-aligned mode is selected or if DIR = 0 (up-counting), else it takes the autoreload value (TIMx_ARR) if DIR = 1 (down-counting).

31.5.7 TIMx capture/compare mode register 1 (TIMx_CCMR1)(x = 2 to 4)

Address offset: 0x018

Reset value: 0x0000 0000

The same register can be used for input capture mode (this section) or for output compare mode (next section). The direction of a channel is defined by configuring the corresponding CCxS bits. All the other bits of this register have a different function for input capture and for output compare modes. It is possible to combine both modes independently (for example channel 1 in input capture mode and channel 2 in output compare mode).

Input capture mode

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:12 IC2F[3:0] : Input capture 2 filter

Bits 11:10 IC2PSC[1:0] : Input capture 2 prescaler

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC2 channel is configured as output.

01: CC2 channel is configured as input, tim_ic2 is mapped on tim_ti2.

10: CC2 channel is configured as input, tim_ic2 is mapped on tim_ti1.

11: CC2 channel is configured as input, tim_ic2 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC2S bits are writable only when the channel is OFF (CC2E = 0 in TIMx_CCER).

This bitfield defines the frequency used to sample tim_ti1 input and the length of the digital filter applied to tim_ti1. The digital filter is made of an event counter in which N consecutive events are needed to validate a transition on the output:

0000: No filter, sampling is done at \( f_{DTS} \)

0001: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 2

0010: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 4

0011: \( f_{SAMPLING} = f_{tim\_ker\_ck} \) , N = 8

0100: \( f_{SAMPLING} = f_{DTS}/2 \) , N = 6

0101: \( f_{SAMPLING} = f_{DTS}/2 \) , N = 8

0110: \( f_{SAMPLING} = f_{DTS}/4 \) , N = 6

0111: \( f_{SAMPLING} = f_{DTS}/4 \) , N = 8

1000: \( f_{SAMPLING} = f_{DTS}/8 \) , N = 6

1001: \( f_{SAMPLING} = f_{DTS}/8 \) , N = 8

1010: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 5

1011: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 6

1100: \( f_{SAMPLING} = f_{DTS}/16 \) , N = 8

1101: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 5

1110: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 6

1111: \( f_{SAMPLING} = f_{DTS}/32 \) , N = 8

This bitfield defines the ratio of the prescaler acting on CC1 input (tim_ic1). The prescaler is reset as soon as CC1E = 0 (TIMx_CCER register).

00: no prescaler, capture is done each time an edge is detected on the capture input

01: capture is done once every 2 events

10: capture is done once every 4 events

11: capture is done once every 8 events

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC1 channel is configured as output

01: CC1 channel is configured as input, tim_ic1 is mapped on tim_ti1

10: CC1 channel is configured as input, tim_ic1 is mapped on tim_ti2

11: CC1 channel is configured as input, tim_ic1 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

31.5.8 TIMx capture/compare mode register 1 [alternate] (TIMx_CCMR1)(x = 2 to 4)

Address offset: 0x018

Reset value: 0x0000 0000

The same register can be used for output compare mode (this section) or for input capture mode (previous section). The direction of a channel is defined by configuring the corresponding CCxS bits. All the other bits of this register have a different function for input capture and for output compare modes. It is possible to combine both modes independently (for example channel 1 in input capture mode and channel 2 in output compare mode).

Output compare mode

Bits 31:25 Reserved, must be kept at reset value.

Bits 23:17 Reserved, must be kept at reset value.

Bit 15 OC2CE : Output compare 2 clear enable

Bits 24, 14:12 OC2M[3:0] : Output compare 2 mode
refer to OC1M description on bits 6:4

Bit 11 OC2PE : Output compare 2 preload enable

Bit 10 OC2FE : Output compare 2 fast enable

Bits 9:8 CC2S[1:0] : Capture/Compare 2 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC2 channel is configured as output

01: CC2 channel is configured as input, tim_ic2 is mapped on tim_ti2

10: CC2 channel is configured as input, tim_ic2 is mapped on tim_ti1

11: CC2 channel is configured as input, tim_ic2 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through the TS bit (TIMx_SMCR register)

Note: CC2S bits are writable only when the channel is OFF (CC2E = 0 in TIMx_CCER).

Bit 7 OC1CE : Output compare 1 clear enable

0: tim_oc1ref is not affected by the tim_ocref_clr_int input

1: tim_oc1ref is cleared as soon as a High level is detected on tim_ocref_clr_int input

Bits 16, 6:4 OC1M[3:0] : Output compare 1 mode

These bits define the behavior of the output reference signal tim_oc1ref from which tim_oc1 is derived. tim_oc1ref is active high whereas tim_oc1 active level depends on CC1P bit.

0000: Frozen - The comparison between the output compare register TIMx_CCR1 and the counter TIMx_CNT has no effect on the outputs. This mode can be used when the timer serves as a software timebase. When the frozen mode is enabled during timer operation, the output keeps the state (active or inactive) it had before entering the frozen state.

0001: Set channel 1 to active level on match. tim_oc1ref signal is forced high when the counter TIMx_CNT matches the capture/compare register 1 ( TIMx_CCR1 ).

0010: Set channel 1 to inactive level on match. tim_oc1ref signal is forced low when the counter TIMx_CNT matches the capture/compare register 1 ( TIMx_CCR1 ).

0011: Toggle - tim_oc1ref toggles when TIMx_CNT = TIMx_CCR1 .

0100: Force inactive level - tim_oc1ref is forced low.

0101: Force active level - tim_oc1ref is forced high.

0110: PWM mode 1 - In up-counting, channel 1 is active as long as TIMx_CNT < TIMx_CCR1 else inactive. In down-counting, channel 1 is inactive ( tim_oc1ref = 0 ) as long as TIMx_CNT > TIMx_CCR1 else active ( tim_oc1ref = 1 ).

0111: PWM mode 2 - In up-counting, channel 1 is inactive as long as TIMx_CNT < TIMx_CCR1 else active. In down-counting, channel 1 is active as long as TIMx_CNT > TIMx_CCR1 else inactive.

1000: Retriggerable OPM mode 1 - In up-counting mode, the channel is active until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channel becomes inactive again at the next update. In down-counting mode, the channel is inactive until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channel becomes inactive again at the next update.

1001: Retriggerable OPM mode 2 - In up-counting mode, the channel is inactive until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 2 and the channel becomes inactive again at the next update. In down-counting mode, the channel is active until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channel becomes active again at the next update.

1010: Reserved.

1011: Reserved.

1100: Combined PWM mode 1 - tim_oc1ref has the same behavior as in PWM mode 1. tim_oc1refc is the logical OR between tim_oc1ref and tim_oc2ref .

1101: Combined PWM mode 2 - tim_oc1ref has the same behavior as in PWM mode 2. tim_oc1refc is the logical AND between tim_oc1ref and tim_oc2ref .

1110: Asymmetric PWM mode 1 - tim_oc1ref has the same behavior as in PWM mode 1. tim_oc1refc outputs tim_oc1ref when the counter is counting up, tim_oc2ref when it is counting down.

1111: Asymmetric PWM mode 2 - tim_oc1ref has the same behavior as in PWM mode 2. tim_oc1refc outputs tim_oc1ref when the counter is counting up, tim_oc2ref when it is counting down.

Note: In PWM mode, the OCREF level changes when the result of the comparison changes, when the output compare mode switches from “frozen” mode to “PWM” mode and when the output compare mode switches from “force active/inactive” mode to “PWM” mode.

Bit 3 OC1PE : Output compare 1 preload enable

0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the new value is taken in account immediately.

1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload register. TIMx_CCR1 preload value is loaded in the active register at each update event.

Bit 2 OC1FE : Output compare 1 fast enable

This bit decreases the latency between a trigger event and a transition on the timer output. It must be used in one-pulse mode (OPM bit set in TIMx_CR1 register), to have the output pulse starting as soon as possible after the starting trigger.

0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is 5 clock cycles.

1: An active edge on the trigger input acts like a compare match on CC1 output. Then, OC is set to the compare level independently from the result of the comparison. Delay to sample the trigger input and to activate CC1 output is reduced to three clock cycles. OCFE acts only if the channel is configured in PWM1 or PWM2 mode.

Bits 1:0 CC1S[1:0] : Capture/Compare 1 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC1 channel is configured as output.

01: CC1 channel is configured as input, tim_ic1 is mapped on tim_ti1.

10: CC1 channel is configured as input, tim_ic1 is mapped on tim_ti2.

11: CC1 channel is configured as input, tim_ic1 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

31.5.9 TIMx capture/compare mode register 2 (TIMx_CCMR2)(x = 2 to 4)

Address offset: 0x01C

Reset value: 0x0000 0000

The same register can be used for input capture mode (this section) or for output compare mode (next section). The direction of a channel is defined by configuring the corresponding CCxS bits. All the other bits of this register have a different function for input capture and for output compare modes. It is possible to combine both modes independently (for example channel 1 in input capture mode and channel 2 in output compare mode).

Input capture mode

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:12 IC4F[3:0] : Input capture 4 filter

Bits 11:10 IC4PSC[1:0] : Input capture 4 prescaler

Bits 9:8 CC4S[1:0] : Capture/Compare 4 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC4 channel is configured as output

01: CC4 channel is configured as input, tim_ic4 is mapped on tim_ti4

10: CC4 channel is configured as input, tim_ic4 is mapped on tim_ti3

11: CC4 channel is configured as input, tim_ic4 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC4S bits are writable only when the channel is OFF (CC4E = 0 in TIMx_CCER).

Bits 7:4 IC3F[3:0] : Input capture 3 filter

Bits 3:2 IC3PSC[1:0] : Input capture 3 prescaler

Bits 1:0 CC3S[1:0] : Capture/Compare 3 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC3 channel is configured as output

01: CC3 channel is configured as input, tim_ic3 is mapped on tim_ti3

10: CC3 channel is configured as input, tim_ic3 is mapped on tim_ti4

11: CC3 channel is configured as input, tim_ic3 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC3S bits are writable only when the channel is OFF (CC3E = 0 in TIMx_CCER).

31.5.10 TIMx capture/compare mode register 2 [alternate]
(TIMx_CCMR2)(x = 2 to 4)

Address offset: 0x01C

Reset value: 0x0000 0000

The same register can be used for output compare mode (this section) or for input capture mode (previous section). The direction of a channel is defined by configuring the corresponding CCxS bits. All the other bits of this register have a different function for input capture and for output compare modes. It is possible to combine both modes independently (for example channel 1 in input capture mode and channel 2 in output compare mode).

Output compare mode

Bits 31:25 Reserved, must be kept at reset value.

Bits 23:17 Reserved, must be kept at reset value.

Bit 15 OC4CE : Output compare 4 clear enable

Bits 24, 14:12 OC4M[3:0] : Output compare 4 mode

Refer to OC3M[3:0]

Bit 11 OC4PE : Output compare 4 preload enable

Bit 10 OC4FE : Output compare 4 fast enable

Bits 9:8 CC4S[1:0] : Capture/Compare 4 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC4 channel is configured as output

01: CC4 channel is configured as input, tim_ic4 is mapped on tim_ti4

10: CC4 channel is configured as input, tim_ic4 is mapped on tim_ti3

11: CC4 channel is configured as input, tim_ic4 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC4S bits are writable only when the channel is OFF (CC4E = 0 in TIMx_CCER).

Bit 7 OC3CE : Output compare 3 clear enable

Bits 16, 6:4 OC3M[3:0] : Output compare 3 mode

These bits define the behavior of the output reference signal tim_oc3ref from which tim_oc3 and tim_oc3n are derived. tim_oc3ref is active high whereas tim_oc3 and tim_oc3n active level depends on CC3P and CC3NP bits.

0000: Frozen - The comparison between the output compare register TIMx_CCR3 and the counter TIMx_CNT has no effect on the outputs. (this mode is used to generate a timing base).

0001: Set channel 3 to active level on match. tim_oc3ref signal is forced high when the counter TIMx_CNT matches the capture/compare register 3 ( TIMx_CCR3 ).

0010: Set channel 3 to inactive level on match. tim_oc3ref signal is forced low when the counter TIMx_CNT matches the capture/compare register 3 ( TIMx_CCR3 ).

0011: Toggle - tim_oc3ref toggles when TIMx_CNT = TIMx_CCR3 .

0100: Force inactive level - tim_oc3ref is forced low.

0101: Force active level - tim_oc3ref is forced high.

0110: PWM mode 1 - In up-counting, channel 3 is active as long as TIMx_CNT < TIMx_CCR3 else inactive. In down-counting, channel 3 is inactive ( tim_oc3ref = 0 ) as long as TIMx_CNT > TIMx_CCR3 else active ( tim_oc3ref = 1 ).

0111: PWM mode 2 - In up-counting, channel 3 is inactive as long as TIMx_CNT < TIMx_CCR3 else active. In down-counting, channel 3 is active as long as TIMx_CNT > TIMx_CCR3 else inactive.

1000: Retriggerable OPM mode 1 - In up-counting mode, the channel is active until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channels becomes active again at the next update. In down-counting mode, the channel is inactive until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channels becomes inactive again at the next update.

1001: Retriggerable OPM mode 2 - In up-counting mode, the channel is inactive until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 2 and the channels becomes inactive again at the next update. In down-counting mode, the channel is active until a trigger event is detected (on tim_trgi signal). Then, a comparison is performed as in PWM mode 1 and the channels becomes active again at the next update.

1010: Pulse on compare: a pulse is generated on tim_oc3ref upon CCR3 match event, as per PWPRSC[2:0] and PW[7:0] bitfields programming in TIMx_ECR .

1011: Direction output. The tim_oc3ref signal is overridden by a copy of the DIR bit.

1100: Combined PWM mode 1 - tim_oc3ref has the same behavior as in PWM mode 1. tim_oc3refc is the logical OR between tim_oc3ref and tim_oc4ref .

1101: Combined PWM mode 2 - tim_oc3ref has the same behavior as in PWM mode 2. tim_oc3refc is the logical AND between tim_oc3ref and tim_oc4ref .

1110: Asymmetric PWM mode 1 - tim_oc3ref has the same behavior as in PWM mode 1. tim_oc3refc outputs tim_oc3ref when the counter is counting up, tim_oc4ref when it is counting down.

1111: Asymmetric PWM mode 2 - tim_oc3ref has the same behavior as in PWM mode 2. tim_oc3refc outputs tim_oc3ref when the counter is counting up, tim_oc4ref when it is counting down.

Note: These bits can not be modified as long as LOCK level 3 has been programmed (LOCK bits in TIMx_BDTR register) and CC1S = 00 (the channel is configured in output).

Note: In PWM mode, the OCREF level changes only when the result of the comparison changes or when the output compare mode switches from “frozen” mode to “PWM” mode.

On channels having a complementary output, this bitfield is preloaded. If the CCPC bit is set in the TIMx_CR2 register then the OC3M active bits take the new value from the preloaded bits only when a COM event is generated.

Bit 3 OC3PE : Output compare 3 preload enable

Bit 2 OC3FE : Output compare 3 fast enable

Bits 1:0 CC3S[1:0] : Capture/Compare 3 selection

This bitfield defines the direction of the channel (input/output) as well as the used input.

00: CC3 channel is configured as output

01: CC3 channel is configured as input, tim_ic3 is mapped on tim_ti3

10: CC3 channel is configured as input, tim_ic3 is mapped on tim_ti4

11: CC3 channel is configured as input, tim_ic3 is mapped on tim_trc. This mode is working only if an internal trigger input is selected through TS bit (TIMx_SMCR register)

Note: CC3S bits are writable only when the channel is OFF (CC3E = 0 in TIMx_CCER).

31.5.11 TIMx capture/compare enable register (TIMx_CCER)(x = 2 to 4)

Address offset: 0x020

Reset value: 0x0000

Bit 15 CC4NP : Capture/Compare 4 output Polarity.

Refer to CC1NP description

Bit 14 Reserved, must be kept at reset value.

Bit 13 CC4P : Capture/Compare 4 output Polarity.

Refer to CC1P description

Bit 12 CC4E : Capture/Compare 4 output enable.

refer to CC1E description

Bit 11 CC3NP : Capture/Compare 3 output Polarity.

Refer to CC1NP description

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC3P : Capture/Compare 3 output Polarity.

Refer to CC1P description

Bit 8 CC3E : Capture/Compare 3 output enable.

Refer to CC1E description

Bit 7 CC2NP : Capture/Compare 2 output Polarity.

Refer to CC1NP description

Bit 6 Reserved, must be kept at reset value.

Bit 5 CC2P : Capture/Compare 2 output Polarity.

refer to CC1P description

Bit 4 CC2E : Capture/Compare 2 output enable.

Refer to CC1E description

Bit 3 CC1NP : Capture/Compare 1 output Polarity.

CC1 channel configured as output: CC1NP must be kept cleared in this case.

CC1 channel configured as input: This bit is used in conjunction with CC1P to define tim_ti1fp1/tim_ti2fp1 polarity. refer to CC1P description.

Bit 2 Reserved, must be kept at reset value.

Bit 1 CC1P : Capture/Compare 1 output Polarity.

0: OC1 active high (output mode) / Edge sensitivity selection (input mode, see below)

1: OC1 active low (output mode) / Edge sensitivity selection (input mode, see below)

When CC1 channel is configured as input, both CC1NP/CC1P bits select the active polarity of TI1FP1 and TI2FP1 for trigger or capture operations.

CC1NP = 0, CC1P = 0: non-inverted/rising edge. The circuit is sensitive to TIxFP1 rising edge (capture or trigger operations in reset, external clock or trigger mode), TIxFP1 is not inverted (trigger operation in gated mode or encoder mode).

CC1NP = 0, CC1P = 1: inverted/falling edge. The circuit is sensitive to TIxFP1 falling edge (capture or trigger operations in reset, external clock or trigger mode), TIxFP1 is inverted (trigger operation in gated mode or encoder mode).

CC1NP = 1, CC1P = 1: non-inverted/both edges. The circuit is sensitive to both TIxFP1 rising and falling edges (capture or trigger operations in reset, external clock or trigger mode), TIxFP1 is not inverted (trigger operation in gated mode). This configuration must not be used in encoder mode.

CC1NP = 1, CC1P = 0: this configuration is reserved, it must not be used.

Bit 0 CC1E : Capture/Compare 1 output enable.

0: Capture mode disabled / OC1 is not active

1: Capture mode enabled / OC1 signal is output on the corresponding output pin

Table 307. Output control bit for standard tim_ocx channels

Note: The state of the external IO pins connected to the standard tim_ocx channels depends only on the GPIO registers when CCxE = 0.

31.5.12 TIM3 counter (TIM3_CNT)

Address offset: 0x024

Reset value: 0x0000 0000

Bit 31 UIFCPY : Value depends on IUFREMAP in TIMx_CR1.

If IUFREMAP = 0

Reserved

If IUFREMAP = 1

UIFCPY : UIF Copy

This bit is a read-only copy of the UIF bit of the TIMx_ISR register

Bits 30:16 Reserved, must be kept at reset value.

Bits 15:0 CNT[15:0] : Counter value

Non-dithering mode (DITHEN = 0)

The register holds the counter value.

Dithering mode (DITHEN = 1)

The register holds the non-dithered part in CNT[15:0]. The fractional part is not available.

31.5.13 TIMx counter (TIMx_CNT)(x = 2, 4)

Address offset: 0x024

Reset value: 0x0000 0000

Bit 31 UIFCPY_CNT[31] : Value depends on IUFREMAP in TIMx_CR1.

If IUFREMAP = 0

CNT[31] : Most significant bit of counter value

If IUFREMAP = 1

UIFCPY : UIF Copy

This bit is a read-only copy of the UIF bit of the TIMx_ISR register

Bits 30:0 CNT[30:0] : Least significant part of counter value

Non-dithering mode (DITHEN = 0)

The register holds the counter value.

Dithering mode (DITHEN = 1)

The register holds the non-dithered part in CNT[30:0]. The fractional part is not available.

31.5.14 TIMx prescaler (TIMx_PSC)(x = 2 to 4)

Address offset: 0x028

Reset value: 0x0000

Bits 15:0 PSC[15:0] : Prescaler value

The counter clock frequency tim_cnt_ck is equal to \( f_{tim\_psc\_ck} / (PSC[15:0] + 1) \) .

PSC contains the value to be loaded in the active prescaler register at each update event (including when the counter is cleared through UG bit of TIMx_EGR register or through trigger controller when configured in “reset mode”).

31.5.15 TIM3 autoreload register (TIM3_ARR)

Address offset: 0x02C

Reset value: 0x0000 FFFF

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:0 ARR[19:0] : Low autoreload value

ARR is the value to be loaded in the actual autoreload register.

Refer to the Section 31.4.3: Time-base unit for more details about ARR update and behavior.

The counter is blocked while the autoreload value is null.

Non-dithering mode (DITHEN = 0)

The register holds the autoreload value.

Dithering mode (DITHEN = 1)

The register holds the integer part in ARR[19:4]. The ARR[3:0] bitfield contains the dithered part.

31.5.16 TIMx autoreload register (TIMx_ARR)(x = 2, 4)

Address offset: 0x02C

Reset value: 0xFFFF FFFF

Bits 31:0 ARR[31:0] : Autoreload value

ARR is the value to be loaded in the actual autoreload register.

Refer to the Section 31.4.3: Time-base unit for more details about ARR update and behavior.

The counter is blocked while the autoreload value is null.

Non-dithering mode (DITHEN = 0)

The register holds the autoreload value.

Dithering mode (DITHEN = 1)

The register holds the integer part in ARR[31:4]. The ARR[3:0] bitfield contains the dithered part.

31.5.17 TIM3 capture/compare register 1 (TIM3_CCR1)

Address offset: 0x034

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:0 CCR1[19:0] : Capture/compare 1 value

If channel CC1 is configured as output:

CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit OC1PE). Else the preload value is copied in the active capture/compare 1 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc1 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value in CCR1[15:0]. The CCR1[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR1[19:4]. The CCR1[3:0] bitfield contains the dithered part.

If channel CC1 is configured as input:

CCR1 is the counter value transferred by the last input capture 1 event (tim_ic1). The TIMx_CCR1 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The CCR1[15:0] bits hold the capture value. The CCR1[19:16] bits are reserved.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR1[19:0]. The CCR1[3:0] bits are reset.

31.5.18 TIMx capture/compare register 1 (TIMx_CCR1)(x = 2, 4)

Address offset: 0x034

Reset value: 0x0000 0000

Bits 31:0 CCR1[31:0] : Capture/compare 1 value

If channel CC1 is configured as output:

CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit OC1PE). Else the preload value is copied in the active capture/compare 1 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc1 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR1[31:4]. The CCR1[3:0] bitfield contains the dithered part.

If channel CC1 is configured as input:

CCR1 is the counter value transferred by the last input capture 1 event (tim_ic1). The TIMx_CCR1 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The register holds the capture value.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR1[31:0]. The CCR1[3:0] bits are reset.

31.5.19 TIM3 capture/compare register 2 (TIM3_CCR2)

Address offset: 0x038

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:0 CCR2[19:0] : Capture/compare 1 value

If channel CC2 is configured as output:

CCR2 is the value to be loaded in the actual capture/compare 2 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR2 register (bit OC2PE). Else the preload value is copied in the active capture/compare 2 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc2 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value in CCR2[15:0]. The CCR2[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR2[19:4]. The CCR2[3:0] bitfield contains the dithered part.

If channel CC2 is configured as input:

CCR2 is the counter value transferred by the last input capture 2 event (tim_ic2). The TIMx_CCR2 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The CCR2[15:0] bits hold the capture value. The CCR2[19:16] bits are reserved.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR2[19:0]. The CCR2[3:0] bits are reset.

31.5.20 TIMx capture/compare register 2 (TIMx_CCR2)(x = 2, 4)

Address offset: 0x038

Reset value: 0x0000 0000

Bits 31:0 CCR2[31:0] : Capture/compare 2 value

If channel CC2 is configured as output:

CCR2 is the value to be loaded in the actual capture/compare 2 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR2 register (bit OC2PE). Else the preload value is copied in the active capture/compare 2 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc2 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR2[31:4]. The CCR2[3:0] bitfield contains the dithered part.

If channel CC2 is configured as input:

CCR2 is the counter value transferred by the last input capture 2 event (tim_ic2). The TIMx_CCR2 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The register holds the capture value.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR2[31:0]. The CCR2[3:0] bits are reset.

31.5.21 TIM3 capture/compare register 3 (TIM3_CCR3)

Address offset: 0x03C

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:0 CCR3[19:0] : Capture/compare 3 value

If channel CC3 is configured as output:

CCR3 is the value to be loaded in the actual capture/compare 3 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR3 register (bit OC3PE). Else the preload value is copied in the active capture/compare 3 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc3 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value in CCR3[15:0]. The CCR3[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR3[19:4]. The CCR3[3:0] bitfield contains the dithered part.

If channel CC3 is configured as input:

CCR3 is the counter value transferred by the last input capture 3 event (tim_ic3). The TIMx_CCR3 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The CCR3[15:0] bits hold the capture value. The CCR3[19:16] bits are reserved.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR3[19:0]. The CCR3[3:0] bits are reset.

31.5.22 TIMx capture/compare register 3 (TIMx_CCR3)(x = 2, 4)

Address offset: 0x03C

Reset value: 0x0000 0000

Bits 31:0 CCR3[31:0] : Capture/compare 3 value

If channel CC3 is configured as output:

CCR3 is the value to be loaded in the actual capture/compare 3 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR3 register (bit OC3PE). Else the preload value is copied in the active capture/compare 3 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc3 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR3[31:4]. The CCR3[3:0] bitfield contains the dithered part.

If channel CC3 is configured as input:

CCR3 is the counter value transferred by the last input capture 3 event (tim_ic3). The TIMx_CCR3 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The register holds the capture value.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR3[31:0]. The CCR3[3:0] bits are reset.

31.5.23 TIM3 capture/compare register 4 (TIM3_CCR4)

Address offset: 0x040

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:0 CCR4[19:0] : Capture/compare 4 value

If channel CC4 is configured as output:

CCR4 is the value to be loaded in the actual capture/compare 4 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR4 register (bit OC4PE). Else the preload value is copied in the active capture/compare 4 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc4 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value in CCR4[15:0]. The CCR4[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR4[19:4]. The CCR4[3:0] bitfield contains the dithered part.

If channel CC4 is configured as input:

CCR4 is the counter value transferred by the last input capture 4 event (tim_ic4). The TIMx_CCR4 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The CCR4[15:0] bits hold the capture value. The CCR4[19:16] bits are reserved.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR4[19:0]. The CCR4[3:0] bits are reset.

31.5.24 TIMx capture/compare register 4 (TIMx_CCR4)(x = 2, 4)

Address offset: 0x040

Reset value: 0x0000 0000

Bits 31:0 CCR4[31:0] : Capture/compare 4 value

If channel CC4 is configured as output:

CCR4 is the value to be loaded in the actual capture/compare 4 register (preload value). It is loaded permanently if the preload feature is not selected in the TIMx_CCMR4 register (bit OC4PE). Else the preload value is copied in the active capture/compare 4 register when an update event occurs.

The active capture/compare register contains the value to be compared to the counter TIMx_CNT and signaled on tim_oc4 output.

Non-dithering mode (DITHEN = 0)

The register holds the compare value.

Dithering mode (DITHEN = 1)

The register holds the integer part in CCR4[31:4]. The CCR4[3:0] bitfield contains the dithered part.

If channel CC4 is configured as input:

CCR4 is the counter value transferred by the last input capture 4 event (tim_ic4). The TIMx_CCR4 register is read-only and cannot be programmed.

Non-dithering mode (DITHEN = 0)

The register holds the capture value.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR4[31:0]. The CCR4[3:0] bits are reset.

31.5.25 TIMx timer encoder control register (TIMx_ECR)(x = 2 to 4)

Address offset: 0x058

Reset value: 0x0000 0000

Bits 31:27 Reserved, must be kept at reset value.

Bits 26:24 PWPRSC[2:0] : Pulse width prescaler

This bitfield sets the clock prescaler for the pulse generator, as following:

Bits 23:16 PW[7:0] : Pulse width

This bitfield defines the pulse duration, as following:

Bits 15:8 Reserved, must be kept at reset value.

In quadrature encoder mode (SMS[3:0] = 0001, 0010, 0011, 1110, 1111), this bit indicates in which AB input configuration the Index event resets the counter.

• 00: Index resets the counter when AB = 00
• 01: Index resets the counter when AB = 01
• 10: Index resets the counter when AB = 10
• 11: Index resets the counter when AB = 11

In directional clock mode or clock plus direction mode (SMS[3:0] = 1010, 1011, 1100, 1101), these bits indicates on which level the Index event resets the counter. In bidirectional clock mode, this applies for both clock inputs.

• x0: Index resets the counter when clock is 0
• x1: Index resets the counter when clock is 1

Note: IPOS[1] bit is not significant

This bit indicates if the first index only is taken into account

• 0: Index is always active
• 1: the first Index only resets the counter

This bit indicates if the Index event is conditioned by the tim_ti3 input

• 00: Index always active
• 01: Index disabled when tim_ti3 input is active, as per CC3P bitfield
• 10: Index disabled when tim_ti4 input is active, as per CC4P bitfield
• 11: Reserved

This bit indicates in which direction the Index event resets the counter.

• 00: Index resets the counter whatever the direction
• 01: Index resets the counter when up-counting only
• 10: Index resets the counter when down-counting only
• 11: Reserved

This bit indicates if the Index event resets the counter.

• 0: Index disabled
• 1: Index enabled

31.5.26 TIMx timer input selection register (TIMx_TISEL)(x = 2 to 4)

Address offset: 0x05C

Reset value: 0x0000 0000

Bits 31:28 Reserved, must be kept at reset value.

Bits 27:24 TI4SEL[3:0] : Selects tim_ti4[15:0] input

0000: tim_ti4_in0: TIMx_CH4
0001: tim_ti4_in1
...
1111: tim_ti4_in15

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

Bits 23:20 Reserved, must be kept at reset value.

Bits 19:16 TI3SEL[3:0] : Selects tim_ti3[15:0] input

0000: tim_ti3_in0: TIMx_CH3
0001: tim_ti3_in1
...
1111: tim_ti3_in15

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

Bits 15:12 Reserved, must be kept at reset value.

Bits 11:8 TI2SEL[3:0] : Selects tim_ti2[15:0] input

0000: tim_ti2_in0: TIMx_CH2
0001: tim_ti2_in1
...
1111: tim_ti2_in15

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

Bits 7:4 Reserved, must be kept at reset value.

Bits 3:0 TI1SEL[3:0] : Selects tim_ti1[15:0] input

0000: tim_ti1_in0: TIMx_CH1
0001: tim_ti1_in1
...
1111: tim_ti1_in15

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

31.5.27 TIMx alternate function register 1 (TIMx_AF1)(x = 2 to 4)

Address offset: 0x060

Reset value: 0x0000 0000

Bits 31:18 Reserved, must be kept at reset value.

Bits 17:14 ETRSEL[3:0] : etr_in source selection

These bits select the etr_in input source.

0000: tim_etr0: TIMx_ETR input

0001: tim_etr1

...

1111: tim_etr15

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

Bits 13:0 Reserved, must be kept at reset value.

31.5.28 TIMx alternate function register 2 (TIMx_AF2)(x = 2 to 4)

Address offset: 0x064

Reset value: 0x0000 0000

Bits 31:19 Reserved, must be kept at reset value.

Bits 18:16 OCRSEL[2:0] : ocref_clr source selection

These bits select the ocref_clr input source.

000: tim_ocref_clr0

001: tim_ocref_clr1

...

111: tim_ocref_clr7

Refer to Section 31.4.2: TIM2/TIM3/TIM4 pins and internal signals for product specific implementation.

Bits 15:0 Reserved, must be kept at reset value.

31.5.29 TIMx DMA control register (TIMx_DCR)(x = 2 to 4)

Address offset: 0x3DC

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bits 19:16 DBSS[3:0] : DMA burst source selection

This bitfield defines the interrupt source that triggers the DMA burst transfers (the timer recognizes a burst transfer when a read or a write access is done to the TIMx_DMAR address).

0000: Reserved

0001: Update

0010: CC1

0011: CC2

0100: CC3

0101: CC4

0110: COM

0111: Trigger

Others: reserved

Bits 15:13 Reserved, must be kept at reset value.

This 5-bit vector defines the length of DMA transfers (the timer recognizes a burst transfer when a read or a write access is done to the TIMx_DMAR address), i.e. the number of transfers. Transfers can be in half-words or in bytes (see example below).

• 00000: 1 transfer
• 00001: 2 transfers
• 00010: 3 transfers
• ...
• 11010: 26 transfers

Example: Let us consider the following transfer: DBL = 7 bytes & DBA = TIM2_CR1.

–If DBL = 7 bytes and DBA = TIM2_CR1 represents the address of the byte to be transferred, the address of the transfer is given by the following equation:

In this example, 7 bytes are added to (TIMx_CR1 address) + DBA, which gives us the address from/to which the data are copied. In this case, the transfer is done to 7 registers starting from the following address: (TIMx_CR1 address) + DBA

According to the configuration of the DMA Data Size, several cases may occur:

–If the DMA Data Size is configured in half-words, 16-bit data are transferred to each of the 7 registers.

–If the DMA Data Size is configured in bytes, the data are also transferred to 7 registers: the first register contains the first MSB byte, the second register, the first LSB byte and so on. So with the transfer Timer, one also has to specify the size of data transferred by DMA.

Bits 7:5 Reserved, must be kept at reset value.

This 5-bits vector defines the base-address for DMA transfers (when read/write access are done through the TIMx_DMAR address). DBA is defined as an offset starting from the address of the TIMx_CR1 register.

Example:

• 00000: TIMx_CR1,
• 00001: TIMx_CR2,
• 00010: TIMx_SMCR,
• ...

31.5.30 TIMx DMA address for full transfer (TIMx_DMAR)(x = 2 to 4)

Address offset: 0x3E0

Reset value: 0x0000 0000

Bits 31:0 DMAB[31:0] : DMA register for burst accesses

A read or write operation to the DMAR register accesses the register located at the address

(TIMx_CR1 address) + (DBA + DMA index) x 4

where TIMx_CR1 address is the address of the control register 1, DBA is the DMA base address configured in TIMx_DCR register, DMA index is automatically controlled by the DMA transfer, and ranges from 0 to DBL (DBL configured in TIMx_DCR).

31.5.31 TIMx register map

TIMx registers are mapped as described in the table below.

Table 308. TIM2/TIM3/TIM4 register map and reset values

Table 308. TIM2/TIM3/TIM4 register map and reset values (continued)