40. General-purpose timers (TIM12)

TIM12 is available on STM32U3B5/3C5 devices only. Refer to the device datasheet for more details.

40.1 TIM12 introduction

The TIM12 general-purpose timers consist in a 16-bit autoreload counter driven by a programmable prescaler.

They may be used for a variety of purposes, including measuring the pulse lengths of input signals (input capture) or generating output waveforms (output compare, 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 TIM12 timers are completely independent, and do not share any resources. They can be synchronized together as described in Section 40.3.20: Timer synchronization (TIM12 only) .

40.2 TIM12 main features

The features of the TIM12 general-purpose timer include:

• • 16-bit autoreload upcounter
• • 16-bit programmable prescaler used to divide the counter clock frequency by any factor between 1 and 65536 (can be changed “on the fly”)
• • Up to two independent channels for:
  • – Input capture
  • – Output compare
  • – PWM generation (edge-aligned mode)
  • – One-pulse mode output
• • Synchronization circuit to control the timer with external signals and to interconnect several timers together
• • Interrupt generation on the following events:
  • – Update: counter overflow, counter initialization (by software or internal trigger)
  • – Trigger event (counter start, stop, initialization, or count by internal trigger)
  • – Input capture
  • – Output compare

40.3 TIM12 functional description

40.3.1 Block diagram

Figure 543. General-purpose timer block diagram (TIM12)

40.3.2 TIM12 pins and internal signals

Table 426 and Table 427 in this section summarize the TIM inputs and outputs.

Table 426. TIM input/output pins

1. Available for TIM12 only.

Table 427. TIM internal input/output signals

1. Available for TIM12 only.

Table 428 and Table 429 list the sources connected to the tim_ti[2:1] input multiplexers.

Table 428. Interconnect to the tim_ti1 input multiplexer

Table 429. Interconnect to the tim_ti2 input multiplexer

Table 430 lists the internal sources connected to the tim_itr input multiplexer.

Table 430. TIMx internal trigger connection

40.3.3 Time-base unit

The main block of the timer is a 16-bit up-counter with its related autoreload register. 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 auto-reload 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 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 details 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 counter starts counting one clock cycle after setting the CEN bit in the TIMx_CR1 register.

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 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 544 and Figure 545 give some examples of the counter behavior when the prescaler ratio is changed on the fly.

Figure 544. Counter timing diagram with prescaler division change from 1 to 2

Figure 545. Counter timing diagram with prescaler division change from 1 to 4

40.3.4 Counter modes

Upcounting mode

In upcounting 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.

Setting the UG bit in the TIMx_EGR register (by software or by using the slave mode controller on TIM12) also generates an update event.

The UEV event can be disabled by software by setting the UDIS bit in the 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 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 autoreload shadow register is updated with the preload value (TIMx_ARR).
• • The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC register).

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

Figure 546. Counter timing diagram, internal clock divided by 1

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Figure 547. Counter timing diagram, internal clock divided by 2

Figure 548. Counter timing diagram, internal clock divided by 4

Figure 549. Counter timing diagram, internal clock divided by N

Figure 550. Counter timing diagram, update event when ARPE = 0 (TIMx_ARR not preloaded)

Figure 551. Counter timing diagram, update event when ARPE = 1 (TIMx_ARR preloaded)

40.3.5 Clock selection

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

• • Internal clock (tim_ker_ck)
• • External clock mode1 (for TIM12): external input pin (tim_ti1 or tim_ti2, if available)
• • Internal trigger inputs (tim_itrx) (for TIM12): connecting the trigger output from another timer. For instance, another timer can be configured as a prescaler for TIM12. Refer to Section : Using one timer as prescaler for another timer for more details.

Internal clock source (tim_ker_ck)

For TIM12, the internal clock source is selected when the slave mode controller is disabled (SMS = 000). The CEN bit in the TIMx_CR1 register and the UG bit in the TIMx_EGR register are then used as control bits and can be changed only by software (except for UG which remains cleared). As soon as the CEN bit is programmed to 1, the prescaler is clocked by the internal clock tim_ker_ck.

Figure 552 shows the behavior of the control circuit and the upcounter in normal mode, without prescaler.

Figure 552. 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 553. tim_ti2 external clock connection example

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 IC2F[3:0] bits in the TIMx_CCMR1 register (if no filter is needed, keep IC2F = 0000 ).
4. 4. Select the rising edge polarity by writing CC2P = 0 and CC2NP = 0 in the TIMx_CCER register.
5. 5. Configure the timer in external clock mode 1 by writing SMS = 111 in the TIMx_SMCR register.
6. 6. Select tim_ti2 as the trigger input source by writing TS = 110 in the TIMx_SMCR register.
7. 7. Enable the counter by writing CEN = 1 in the TIMx_CR1 register.

Note: The capture prescaler is not used for triggering, it is not necessary to configure it.

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 554. Control circuit in external clock mode 1

40.3.6 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).

Figure 555 , Figure 556 and Figure 557 give an overview of a 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 555. Capture/compare channel 1 input stage (TIM12)

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 556. Capture/compare channel 1 main circuit

Figure 557. Output stage of capture/compare channel 1

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.

40.3.7 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 tim_icx signal. When a capture occurs, the corresponding CCxIF flag (TIMx_SR register) is set and an interrupt 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_ti1_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 mode, and the TIMx_CCR1 register becomes read-only.
3. 3. Program the appropriate input filter duration in relation with the signal connected to the timer (by programming the ICxF bits in the TIMx_CCMRx register if the input is one of the tim_tix inputs). Let's imagine that, when toggling, the input signal is not stable during at most five internal clock cycles. The user must program a filter duration longer than these five clock cycles. The user 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.

1. 4. Select the edge of the active transition on the tim_ti1 channel by programming CC1P and CC1NP bits to 00 in the TIMx_CCER register (rising edge in this case).
2. 5. Program the input prescaler. In this example, the user wishes the capture to be performed at each valid transition, so the prescaler is disabled (write IC1PS bits to 00 in the TIMx_CCMR1 register).
3. 6. Enable capture from the counter into the capture register by setting the CC1E bit in the TIMx_CCER register.
4. 7. If needed, enable the related interrupt request by setting the CC1IE 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.

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 requests can be generated by software by setting the corresponding CCxG bit in the TIMx_EGR register.

40.3.8 PWM input mode (TIM12 only)

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

For example, one can measure the period (in TIMx_CCR1 register) and the duty cycle (in TIMx_CCR2 register) of the PWM applied on tim_ti1 using the following procedure (depending on tim_ker_ck frequency and prescaler value):

1. 1. Select the proper tim_ti1_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): program the CC1P and CC1NP bits to 00 (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).

1. 5. Select the active polarity for tim_ti1fp2 (used for capture in TIMx_CCR2): program the CC2P and CC2NP bits to 10 (active on falling edge).
2. 6. Select the valid trigger input: write the TS bits to 00101 in the TIMx_SMCR register (tim_ti1fp1 selected).
3. 7. Configure the slave mode controller in reset mode: write the SMS bits to 100 in the TIMx_SMCR register.
4. 8. Enable the captures: write the CC1E and CC2E bits to 1 in the TIMx_CCER register.

Figure 558. PWM input mode timing

40.3.9 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, one just needs to write 0101 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.

The tim_ocxref signal can be forced low by writing the OCxM bits to 0100 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 requests can be sent accordingly. This is described in the output compare mode section below.

40.3.10 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:

1. 1. 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 = 0000), be set active (OCxM = 0001), be set inactive (OCxM = 0010) or can toggle (OCxM = 0011) on match.
2. 2. Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).
3. 3. Generates an interrupt if the corresponding interrupt mask is set (CCxIE bit in the TIMx_DIER register).

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 bit if an interrupt request is to be generated.
4. 4. Select the output mode. For example:
   • – Write OCxM = 0011 to toggle tim_ocx output pin when CNT matches CCRx
   • – Write OCxPE = 0 to disable preload register
   • – Write CCxP = 0 to select active high polarity
   • – 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 559 .

Figure 559. Output compare mode, toggle on tim_oc1.

40.3.11 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 0110 (PWM mode 1) or 0111 (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 upcounting 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.

The 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. The 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 \( TIMx\_CNT \leq TIMx\_CCRx \) .

The timer is able to generate PWM in edge-aligned mode only since the counter is upcounting.

In the following example, the user considers 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 560 shows some edge-aligned PWM waveforms in an example where \( TIMx\_ARR = 8 \) .

Figure 560. Edge-aligned PWM waveforms (ARR = 8)

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 561 presents the dithering principle applied to four consecutive PWM cycles.

Figure 561. Dithering principle

When the dithering mode is enabled, the register coding is changed as follows (see Figure 562 for example):

• • The four LSBs are coding for the enhanced resolution part (fractional part).
• • The MSBs are left-shifted to the bits 19:4 and are coding for the base value.

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 562. Data format and register coding in dithering mode

The minimum frequency is given by the following formula:

Note: The maximum TIMx_ARR and TIMxCCRy values are limited to 0xFFFEF in dithering mode (corresponds to 65534 for the integer part and 15 for the dithered part).

As shown on Figure 563 , the dithering mode is used to increase the PWM resolution whatever the PWM frequency.

Figure 563. PWM resolution vs frequency

The duty cycle and/or period changes are spread over 16 consecutive periods, as described in Figure 564 .

Figure 564. PWM dithering pattern

The autoreload and compare values increments are spread following specific patterns described in Table 431 . The dithering sequence is done to have increments distributed as evenly as possible and minimize the overall ripple.

Table 431. CCR and ARR register change dithering pattern

Table 431. CCR and ARR register change dithering pattern (continued)

40.3.12 Combined PWM mode (TIM12 only)

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 the TIMx_CCR1 and TIMx_CCR2 registers.

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 a combined PWM channel, its complementary 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 565 represents 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 2.
• • Channel 2 is configured in PWM mode 1.

Figure 565. Combined PWM mode on channel 1 and 2

40.3.13 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 as follows:

Figure 566. Example of one pulse mode

For example one may want 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 to 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 \( t_{DELAY} \) is defined by the value written in the TIMx_CCR1 register.
• • The \( t_{PULSE} \) is defined by the difference between the autoreload value and the compare value ( \( TIMx\_ARR - TIMx\_CCR1 \) ).
• • Assuming 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 = 0111 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.

Since only one pulse (Single mode) is needed, a 1 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 \( t_{\text{DELAY min}} \) that can be obtained.

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) are 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.

40.3.14 Retriggerable one pulse mode (TIM12 only)

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 nonretriggerable one pulse mode described in Section 40.3.13: One-pulse mode :

• • 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: The OCxM[3:0] and SMS[3:0] bit fields are split into two parts for compatibility reasons, the most significant bit are 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 567. Retriggerable one pulse mode

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40.3.15 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 (TIMxCNT[31]). This is used to atomically read both the counter value and a potential roll-over condition signaled by the UIFCPY flag. In particular cases, it can ease the calculations 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 assertions of the UIF and UIFCPY flags.

40.3.16 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 two input pins tim_ti1 and tim_ti2.

The XOR output can be used with all the timer input functions such as trigger or input capture. It is useful for measuring the interval between the edges on two input signals, as shown in Figure 568.

Figure 568. Measuring time interval between edges on 2 signals

40.3.17 TIM12 external trigger synchronization

The TIM12 timer can be synchronized with an external trigger in several modes: Reset mode, Gated mode, Trigger mode, Reset + trigger, and Gated + reset mode.

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, the user does not need any filter, so the user keeps 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. Program CC1P and CC1NP to 00 in TIMx_CCER register to validate the polarity (and detect rising edges only).

1. 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.
2. 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 can be sent if enabled (depending on the TIE bit 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 569. 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. Configure the channel 1 to detect low levels on tim_ti1. Configure the input filter duration (in this example, the user does not need any filter, so the user keeps 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. Program CC1P = 1 and CC1NP = 0 in TIMx_CCER register to validate the polarity (and detect low level only).
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. 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 570. Control circuit in gated mode

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, the user does not need any filter, so the user keeps IC2F = 0000). The capture prescaler is not used for triggering, so it does not need to be configured. The CC2S bits are configured to select the input capture source only, CC2S = 01 in TIMx_CCMR1 register. Program 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 571. Control circuit in trigger mode

40.3.18 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.

40.3.19 Slave mode – combined reset + gated 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.

40.3.20 Timer synchronization (TIM12 only)

The TIMx timers are linked together internally for timer synchronization or chaining. Refer to Section 38.4.23: Timer synchronization for details.

Note: The clock of the slave timer 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.

40.3.21 Using timer output as trigger for other timers (N/A only)

The timers with one channel only do not feature a master mode. However, the OC1 output signal can be used to trigger some other timers (including timers described in other sections of this document). Check the “TIMx internal trigger connection” table of any timer on the device to identify which timers can be targeted as slave.

The 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's timer CK_INT clock is four times slower than the source timer, the OC1 pulse width must be eight clock cycles.

40.3.22 ADC triggers (TIM12 only)

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.

40.3.23 Debug mode

When the microcontroller enters debug mode (Cortex-M33 core halted), the TIMx counter can either continue to work normally or stop.

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 the Debug section.

40.4 TIM12 low-power modes

Table 432. Effect of low-power modes on TIM12

40.5 TIM12 interrupts

The TIM12 can generate multiple interrupts, as shown in Table 433 .

Table 433. Interrupt requests

1. Available for TIM12 only.

40.6 TIM12 registers

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

The peripheral registers have to be written by half-words (16 bits) or words (32 bits). Read accesses can be done by bytes (8 bits), half-words (16 bits), or words (32 bits).

40.6.1 TIM12 control register 1 (TIM12_CR1)

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_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 : Auto-reload preload enable

0: TIMx_ARR register is not buffered.

1: TIMx_ARR register is buffered.

Bits 6:4 Reserved, must be kept at reset value.

Bit 3 OPM : One-pulse mode

0: Counter is not stopped on the update event

1: Counter stops counting on the next update event (clearing the CEN bit).

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 generates an update interrupt if enabled. These events can be:

• – Counter overflow
• – Setting the UG bit
• – Update generation through the slave mode controller

1: Only counter overflow generates an update interrupt if enabled.

Bit 1 UDIS : Update disable

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

0: UEV enabled. An UEV is generated by one of the following events:

• – Counter overflow
• – Setting the UG bit

Buffered registers are then loaded with their preload values.

1: UEV disabled. No UEV is generated, shadow registers keep their value (ARR, PSC, CCRx). The counter and the prescaler are reinitialized if the UG bit is set.

Bit 0 CEN : Counter enable

0: Counter disabled

1: Counter enabled

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

Note: External clock and gated 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.

40.6.2 TIM12 control register 2 (TIM12_CR2)

Address offset: 0x004

Reset value: 0x0000

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

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

1: The tim_ti1_in[15:0] and tim_ti2_in[15:0] multiplexers output are connected to the tim_ti1 input (XOR combination)

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

000: 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.

001: 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 enable. 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).

010: 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.

011: 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).

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

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

Bits 3:0 Reserved, must be kept at reset value.

40.6.3 TIM12 slave mode control register (TIM12_SMCR)

Address offset: 0x008

Reset value: 0x0000 0000

Bits 31:22 Reserved, must be kept at reset value.

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

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

Bit 7 MSM : Master/Slave mode

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 in order to synchronize several timers on a single external event.

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

This TS[4:0] 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)

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 10 (tim_itr11)

10000: Internal Trigger 10 (tim_itr12)

10001: Internal Trigger 10 (tim_itr13)

10010: Internal Trigger 10 (tim_itr14)

10011: Internal Trigger 10 (tim_itr15)

Others: Reserved

See for more details on the meaning of tim_itrx for each timer.

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 Reserved, must be kept at reset value.

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 (see input control register and control register description).

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

0001: Reserved

0010: Reserved

0011: Reserved

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 (but is not reset) as soon as the trigger becomes low. Both start and stop of the counter are controlled.

Other codes: reserved.

Note: The gated mode (including gated + reset 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.

The clock of the slave peripherals (such as timer, ADC) receiving the tim_trgo signals 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.

40.6.4 TIM12 interrupt enable register (TIM12_DIER)

Address offset: 0x00C

Reset value: 0x0000

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

Bit 6 TIE : Trigger interrupt enable

0: Trigger interrupt disabled.

1: Trigger interrupt enabled.

Bits 5:3 Reserved, must be kept at reset value.

Bit 2 CC2IE : Capture/Compare 2 interrupt enable

0: CC2 interrupt disabled.

1: CC2 interrupt enabled.

Bit 1 CC1IE : Capture/Compare 1 interrupt enable

0: CC1 interrupt disabled.

1: CC1 interrupt enabled.

Bit 0 UIE : Update interrupt enable

0: Update interrupt disabled.

1: Update interrupt enabled.

40.6.5 TIM12 status register (TIM12_SR)

Address offset: 0x010

Reset value: 0x0000

Bits 15:11 Reserved, must be kept at reset value.

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.

Bits 5:3 Reserved, must be kept at reset value.

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 3 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 tim_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 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 Section 40.6.3: TIM12 slave mode control register (TIM12_SMCR) ), if URS = 0 and UDIS = 0 in the TIMx_CR1 register.

40.6.6 TIM12 event generation register (TIM12_EGR)

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 the TIMx_SR register. Related interrupt can occur if enabled

Bits 5:3 Reserved, must be kept at reset value.

Bit 2 CC2G : Capture/compare 2 generation

refer to CC1G description

Bit 1 CC1G : Capture/compare 1 generation

This bit is set by software 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:

the CC1IF flag is set, the corresponding interrupt is sent if enabled.

If channel CC1 is configured as input:

The current counter value is captured in the TIMx_CCR1 register. The CC1IF flag is set, the corresponding interrupt 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-initializes the counter and generates an update of the registers. The prescaler counter is also cleared and the prescaler ratio is not affected. The counter is cleared.

40.6.7 TIM12 capture/compare mode register 1 (TIM12_CCMR1)

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 in this register have different functions in input and output modes.

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

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, IC2 is mapped on tim_ti2

10: CC2 channel is configured as input, IC2 is mapped on tim_ti1

11: CC2 channel is configured as input, IC2 is mapped on tim_trc. This mode works only if an internal trigger input is selected through the TS bit (TIMx_SMCR register)

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

This bitfield defines the frequency used to sample the 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 the 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: The CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

40.6.8 TIM12 capture/compare mode register 1 [alternate] (TIM12_CCMR1)

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 in this register have different functions in input and output modes.

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 Reserved, must be kept at reset value.

Bits 24, 14:12 OC2M[3:0] : Output compare 2 mode
Refer to OC1M[3:0] for bit description.

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, IC2 is mapped on tim_ti2

10: CC2 channel is configured as input, IC2 is mapped on tim_ti1

11: CC2 channel is configured as input, IC2 is mapped on tim_trc. This mode works only if an internal trigger input is selected through the TS bit (TIMx_SMCR register)

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

Bit 7 Reserved, must be kept at reset value.

Bits 16, 6:4 OC1M[3:0] : Output compare 1 mode (refer to bit 16 for OC1M[3])

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

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. The tim_oc1ref signal is forced high when the TIMx_CNT counter matches the capture/compare register 1 ( TIMx_CCR1 ).

0010: Set channel 1 to inactive level on match. The tim_oc1ref signal is forced low when the TIMx_CNT counter 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 - channel 1 is active as long as TIMx_CNT < TIMx_CCR1 else it is inactive

0111: PWM mode 2 - channel 1 is inactive as long as TIMx_CNT < TIMx_CCR1 else it is active

1000: Retriggerable OPM mode 1 - 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.

1001: Retriggerable OPM mode 2 - 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.

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: Reserved,

1111: Reserved

Note: In PWM mode, the OREF 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 into account immediately

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

Bit 2 OC1FE : Output compare 1 fast enable

This bit is used to accelerate the effect of an event on the trigger in input on the CC output.

0: CC1 behaves normally depending on the counter and CCR1 values even when the trigger is ON. The minimum delay to activate the 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 the CC1 output. Then, OC is set to the compare level independently of the result of the comparison. Delay to sample the trigger input and to activate CC1 output is reduced to 3 clock cycles. OC1FE 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 works only if an internal trigger input is selected through the TS bit (TIMx_SMCR register)

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

40.6.9 TIM12 capture/compare enable register (TIM12_CCER)

Address offset: 0x020

Reset value: 0x0000

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

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 complementary output Polarity

CC1 channel configured as output: CC1NP must be kept cleared

CC1 channel configured as input: CC1NP is used in conjunction with CC1P to define tim_ti1p1/tim_ti2p1 polarity (refer to CC1P description).

Bit 2 Reserved, must be kept at reset value.

Bit 1 CC1P : Capture/Compare 1 output Polarity.

0: tim_oc1 active high (output mode) / Edge sensitivity selection (input mode, see below)

1: tim_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 tim_ti1fp1 and tim_ti2fp1 for trigger or capture operations.

CC1NP = 0, CC1P = 0: non-inverted/rising edge. The circuit is sensitive to tim_tixfp1 rising edge (capture or trigger operations in reset, external clock or trigger mode), tim_tixfp1 is not inverted (trigger operation in gated mode).

CC1NP = 0, CC1P = 1: inverted/falling edge. The circuit is sensitive to tim_tixfp1 falling edge (capture or trigger operations in reset, external clock or trigger mode), tim_tixfp1 is inverted (trigger operation in gated mode).

CC1NP = 1, CC1P = 1: non-inverted/both edges/ The circuit is sensitive to both tim_tixfp1 rising and falling edges (capture or trigger operations in reset, external clock or trigger mode), tim_tixfp1 is not inverted (trigger operation in gated 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 / tim_oc1 is not active

1: Capture mode enabled / tim_oc1 signal is output on the corresponding output pin

Table 434. Output control bit for standard tim_ocx channels

Note: The states of the external I/O pins connected to the standard tim_ocx channels depend on the state of the tim_ocx channel and on the GPIO registers.

40.6.10 TIM12 counter (TIM12_CNT)

Address offset: 0x024

Reset value: 0x0000 0000

Bit 31 UIFCPY : UIF Copy

This bit is a read-only copy of the UIF bit in 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 only holds the non-dithered part in CNT[15:0]. The fractional part is not available.

40.6.11 TIM12 prescaler (TIM12_PSC)

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 into 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”).

40.6.12 TIM12 autoreload register (TIM12_ARR)

Address offset: 0x02C

Reset value: 0x0000 FFFF

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

Bits 19:0 ARR[19:0] : Auto-reload value

ARR is the value to be loaded in the actual auto-reload register.

Refer to the Section 40.3.3: Time-base unit for more details about ARR update and behavior.

The counter is blocked while the auto-reload value is null.

Non-dithering mode (DITHEN = 0)

The register holds the auto-reload value in ARR[15:0]. The ARR[19:16] bits are reset.

Dithering mode (DITHEN = 1)

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

40.6.13 TIM12 capture/compare register 1 (TIM12_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:

CR1 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 in CCR1[15:0]. The CCR1[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR1[19:4]. The CCR1[3:0] bits are reset.

40.6.14 TIM12 capture/compare register 2 (TIM12_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 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 signalled 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 1 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 in CCR2[15:0]. The CCR2[19:16] bits are reset.

Dithering mode (DITHEN = 1)

The register holds the capture in CCR2[19:4]. The CCR2[3:0] bits are reset.

40.6.15 TIM12 timer input selection register (TIM12_TISEL)

Address offset: 0x05C

Reset value: 0x0000

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

Bits 11:8 TI2SEL[3:0] : selects tim_ti2_in[15:0] input

0000: TIMx_CH2 input (tim_ti2_in0)

0001: tim_ti2_in1

...

0100: tim_ti2_in15

Refer to for interconnects list.

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

Bits 3:0 TI1SEL[3:0] : selects tim_ti1_in[15:0] input

0000: TIMx_CH1 input (tim_ti1_in0)

0001: tim_ti1_in1

...

1111: tim_ti1_in15

Refer to for interconnects list.

40.6.16 TIM12 register map

TIM12 registers are mapped as 16-bit addressable registers as described below:

Table 435. TIM12 register map and reset values

Table 435. TIM12 register map and reset values (continued)

Refer to Section 2.3: Memory organization for the register boundary addresses.

Section 2.3: Memory organization