33. Low-power timer (LPTIM)

33.1 LPTIM introduction

The LPTIM is a 16-bit timer that benefits from the ultimate developments in power consumption reduction. Thanks to its diversity of clock sources, the LPTIM is able to keep running in all power modes except for Standby mode. Given its capability to run even with no internal clock source, the LPTIM can be used as a “Pulse Counter” which can be useful in some applications. The LPTIM capability to wake up the system from low-power modes, makes it suitable to realize “Timeout functions” with extremely low power consumption.

The LPTIM introduces a flexible clock scheme that provides the needed functionalities and performance, while minimizing the power consumption.

33.2 LPTIM main features

• • 16-bit upcounter
• • 3-bit prescaler with 8 possible dividing factors (1,2,4,8,16,32,64,128)
• • Selectable clock
  • – Internal clock sources: configurable internal clock source (see RCC section)
  • – External clock source over LPTIM input (working with no LP oscillator running, used by pulse counter application)
• • 16-bit ARR autoreload register
• • 16-bit capture/compare register
• • Continuous/One-shot mode
• • Selectable software/hardware input trigger
• • Programmable digital glitch filter
• • Configurable output: Pulse, PWM
• • Configurable I/O polarity
• • Encoder mode
• • Repetition counter
• • Up to 2 independent channels for:
  • – Input capture
  • – PWM generation (edge-aligned mode)
  • – One-pulse mode output
• • Interrupt generation on 10 events
• • DMA request generation on the following events:
  • – Update event
  • – Input capture

33.3 LPTIM implementation

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

33.4 LPTIM functional description

33.4.1 LPTIM block diagram

Figure 364. LPTIM block diagram ⁽¹⁾

1. Some I/Os may not be available, refer to Section 33.4.2: LPTIM pins and internal signals .

33.4.2 LPTIM pins and internal signals

The following tables provide the list of LPTIM pins and internal signals, respectively.

Table 323. LPTIM1/2 input/output pins

33.4.3 LPTIM input and trigger mapping

The LPTIM external trigger and input connections are detailed hereafter.

Table 325. LPTIM1/2 external trigger connections

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

Table 326. LPTIM1/2 input 1 connections

Table 327. LPTIM1/2 input 2 connections

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

Table 328. LPTIM1/2 input capture 1 connections

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

Table 329. LPTIM1/2 input capture 2 connections

33.4.4 LPTIM reset and clocks

The LPTIM can be clocked using several clock sources. It can be clocked using an internal clock signal which can be any configurable internal clock source selectable through the RCC (see RCC section for more details). Also, the LPTIM can be clocked using an external clock signal injected on its external Input1. When clocked with an external clock source, the LPTIM can run in one of the following configurations:

• • The first configuration is when the LPTIM is clocked by an external signal but in the same time an internal clock signal is provided to the LPTIM from configurable internal clock source (see RCC section).
• • The second configuration is when the LPTIM is solely clocked by an external clock source through its external Input1. This configuration is the one used to realize Timeout function or pulse counter function when all the embedded oscillators are turned off after entering a low-power mode.

Programming the CKSEL and COUNTMODE bits allows controlling whether the LPTIM uses an external clock source or an internal one.

When configured to use an external clock source, the CKPOL bits are used to select the external clock signal active edge. If both edges are configured to be active ones, an internal clock signal must also be provided (first configuration). In this case, the internal clock signal frequency must be at least four times higher than the external clock signal frequency.

33.4.5 Glitch filter

The LPTIM inputs, either external (mapped to GPIOs) or internal (mapped on the chip-level to other embedded peripherals), are protected with digital filters that prevent any glitches and noise perturbations to propagate inside the LPTIM. This is in order to prevent spurious counts or triggers.

Before activating the digital filters, an internal clock source must first be provided to the LPTIM. This is necessary to guarantee the proper operation of the filters.

The digital filters are divided into three groups:

• • The first group of digital filters protects the LPTIM internal or external inputs. The digital filters sensitivity is controlled by the CKFLT bits
• • The second group of digital filters protects the LPTIM internal or external trigger inputs. The digital filters sensitivity is controlled by the TRGFLT bits.
• • The third group of digital filters protects the LPTIM internal or external input captures. The digital filters sensitivity is controlled by the ICxF bits.

Note: The digital filters sensitivity is controlled by groups. It is not possible to configure each digital filter sensitivity separately inside the same group.

The filter sensitivity acts on the number of consecutive equal samples that is detected on one of the LPTIM inputs to consider a signal level change as a valid transition. Figure 365 shows an example of glitch filter behavior in case of a two consecutive samples programmed.

Figure 365. Glitch filter timing diagram

Note: In case no internal clock signal is provided, the digital filter must be deactivated by setting the CKFLT, ICxF and TRGFLT bits to 0. In this case, an external analog filter can be used to protect the LPTIM external inputs against glitches.

33.4.6 Prescaler

The LPTIM 16-bit counter is preceded by a configurable power-of-2 prescaler. The prescaler division ratio is controlled by the PRESC[2:0] field. The table below lists all the possible division ratios:

Table 330. Prescaler division ratios

33.4.7 Trigger multiplexer

The LPTIM counter can be started either by software or after the detection of an active edge on one of the eight trigger inputs.

TRIGEN[1:0] is used to determine the LPTIM trigger source:

• • When TRIGEN[1:0] equals 00, the LPTIM counter is started as soon as one of the CNTSTRT or the SNGSTRT bits is set by software. The three remaining possible

values for the TRIGEN[1:0] are used to configure the active edge used by the trigger inputs. The LPTIM counter starts as soon as an active edge is detected.

• • When TRIGEN[1:0] is different than 00, TRIGSEL[2:0] is used to select which of the eight trigger inputs is used to start the counter.

The external triggers are considered asynchronous signals for the LPTIM. After a trigger detection, a two-counter-clock period latency is needed before the timer starts running due to the synchronization.

If a new trigger event occurs when the timer is already started it is ignored (unless timeout function is enabled).

Note: The timer must be enabled before setting the SNGSTRT/CNTSTRT bits. Any write on these bits when the timer is disabled is discarded by hardware.

Note: When starting the counter by software (TRIGEN[1:0] = 00), there is a delay of 3 kernel clock cycles between the LPTIM_CR register update (set one of SNGSTRT or CNTSTRT bits) and the effective start of the counter.

33.4.8 Operating mode

The LPTIM features two operating modes:

• • Continuous mode: the timer is free running, the timer is started from a trigger event and never stops until the timer is disabled
• • One-shot mode: the timer is started from a trigger event and stops when an LPTIM update event is generated.

One-shot mode

To enable the one-shot counting, the SNGSTRT bit must be set.

A new trigger event re-starts the timer. Any trigger event occurring after the counter starts and before the next LPTIM update event, is discarded.

In case an external trigger is selected, each external trigger event arriving after the SNGSTRT bit is set, and after the repetition counter has stopped (after the update event), and if the repetition register content is different from zero, the repetition counter gets reloaded with the value already contained by the repetition register and a new one-shot counting cycle is started as shown in Figure 366 .

Figure 366. LPTIM output waveform, single-counting mode configuration when repetition register content is different than zero (with PRELOAD = 1)

- Set-once mode activated:

Note that when the WAVE bitfield in the LPTIM_CFGR register is set, the Set-once mode is activated. In this case, the counter is only started once following the first trigger, and any subsequent trigger event is discarded as shown in Figure 367 .

Figure 367. LPTIM output waveform, single-counting mode configuration and Set-once mode activated (WAVE bit is set)

In case of software start (TRIGEN[1:0] = 00), the SNGSTRT setting starts the counter for one-shot counting.

Continuous mode

To enable the continuous counting, the CNTSTRT bit must be set.

In case an external trigger is selected, an external trigger event arriving after CNTSTRT is set, starts the counter for continuous counting. Any subsequent external trigger event is discarded as shown in Figure 368 .

In case of software start (TRIGEN[1:0] = 00), setting CNTSTRT starts the counter for continuous counting.

Figure 368. LPTIM output waveform, Continuous counting mode configuration

SNGSTRT and CNTSTRT bits can only be set when the timer is enabled (ENABLE bit set to 1). It is possible to change “on the fly” from One-shot mode to Continuous mode.

If the Continuous mode was previously selected, setting SNGSTRT switches the LPTIM to the One-shot mode. The counter (if active) stops as soon as an LPTIM update event is generated.

If the One-shot mode was previously selected, setting CNTSTRT switches the LPTIM to the Continuous mode. The counter (if active) restarts as soon as it reaches ARR.

33.4.9 Timeout function

The detection of an active edge on one selected trigger input can be used to reset the LPTIM counter. This feature is controlled through the TIMEOUT bit.

The first trigger event starts the timer, any successive trigger event resets the LPTIM counter and the repetition counter and the timer restarts.

A low-power timeout function can be realized. The timeout value corresponds to the compare value; if no trigger occurs within the expected time frame, the MCU is waked-up by the compare match event.

33.4.10 Waveform generation

Two 16-bit registers, the LPTIM_ARR (autoreload register) and LPTIM_CCRx (capture/compare register), are used to generate several different waveforms on LPTIM output

The timer can generate the following waveforms:

• • The PWM mode: the LPTIM output is set as soon as the counter value in LPTIM_CNT exceeds the compare value in LPTIM_CCRx. The LPTIM output is reset as soon as a match occurs between the LPTIM_ARR and the LPTIM_CNT register. For more details see Section 33.4.19: PWM mode .
• • The One-pulse mode: the output waveform is similar to the one of the PWM mode for the first pulse, then the output is permanently reset
• • The Set-once mode: the output waveform is similar to the One-pulse mode except that the output is kept to the last signal level (depends on the output configured polarity).

The above described modes require the LPTIM_ARR register value to be strictly greater than the LPTIM_CCRx register value.

The LPTIM output waveform can be configured through the WAVE bit as follow:

• • Resetting the WAVE bit to 0 forces the LPTIM to generate either a PWM waveform or a One pulse waveform depending on which bit is set: CNTSTRT or SNGSTRT.
• • Setting the WAVE bit to 1 forces the LPTIM to generate a Set-once mode waveform.

The CCxP bit controls the LPTIM output polarity. The change takes effect immediately, so the output default value changes immediately after the polarity is re-configured, even before the timer is enabled.

Signals with frequencies up to the LPTIM clock frequency divided by two can be generated. Figure 369 below shows the three possible waveforms that can be generated on the LPTIM output. Also, it shows the effect of the polarity change using the CCxP bit.

Figure 369. Waveform generation

33.4.11 Register update

The LPTIM_ARR register, the LPTIM_RCR register and the LPTIM_CCRx register are updated immediately after the APB bus write operation or in synchronization with the next LPTIM update event if the timer is already started.

The PRELOAD bit controls how the LPTIM_ARR, the LPTIM_RCR and the LPTIM_CCRx registers are updated:

• • When the PRELOAD bit is reset to 0, the LPTIM_ARR, the LPTIM_RCR and the LPTIM_CCRx registers are immediately updated after any write access.
• • When the PRELOAD bit is set to 1, the LPTIM_ARR, the LPTIM_RCR and the LPTIM_CCRx registers are updated at next LPTIM update event, if the timer has been already started.

The LPTIM APB interface and the LPTIM kernel logic use different clocks, so there is some latency between the APB write and the moment when these values are available to the counter comparator. Within this latency period, any additional write into these registers must be avoided.

The ARROK flag, the REPOK flag and the CMPxOK flag in the LPTIM_ISR register indicate when the write operation is completed to respectively the LPTIM_ARR register, the LPTIM_RCR register and the LPTIM_CCRx register.

After a write to the LPTIM_ARR, the LPTIM_RCR or the LPTIM_CCRx register, a new write operation to the same register can only be performed when the previous write operation is completed. Any successive write before respectively the ARROK flag, the REPOK flag or the CMPxOK flag be set, leads to unpredictable results.

33.4.12 Counter mode

The LPTIM counter can be used to count external events on the LPTIM input1 or it can be used to count internal clock cycles. The CKSEL and COUNTMODE bits control which source is used for updating the counter.

In case the LPTIM is configured to count external events on Input1, the counter can be updated following a rising edge, falling edge or both edges depending on the value written to the CKPOL[1:0] bits.

The count modes below can be selected, depending on CKSEL and COUNTMODE values:

• • CKSEL = 0: the LPTIM is clocked by an internal clock source
  • – COUNTMODE = 0
    The LPTIM is configured to be clocked by an internal clock source and the LPTIM counter is configured to be updated following each internal clock pulse.
  • – COUNTMODE = 1
    The LPTIM external Input1 is sampled with the internal clock provided to the LPTIM.
    Consequently, in order not to miss any event, the frequency of the changes on the external Input1 signal must never exceed the frequency of the internal clock provided to the LPTIM. Also, the internal clock provided to the LPTIM must not be prescaled (PRESC[2:0] = 000).
• • CKSEL = 1: the LPTIM is clocked by an external clock source
  COUNTMODE value is don't care.
  In this configuration, the LPTIM has no need for an internal clock source (except if the glitch filters are enabled). The signal injected on the LPTIM external input1 is used as

system clock for the LPTIM. This configuration is suitable for operation modes where no embedded oscillator is enabled.

For this configuration, the LPTIM counter can be updated either on rising edges or falling edges of the input1 clock signal but not on both rising and falling edges.

Since the signal injected on the LPTIM external input1 is also used to clock the LPTIM kernel logic, there is some initial latency (after the LPTIM is enabled) before the counter is incremented. More precisely, the first five active edges on the LPTIM external Input1 (after LPTIM is enable) are lost.

33.4.13 Timer enable

The ENABLE bit located in the LPTIM_CR register is used to enable/disable the LPTIM kernel logic. After setting the ENABLE bit, a delay of two counter clock cycles is needed before the LPTIM is actually enabled.

The LPTIM_CFGR register must be modified only when the LPTIM is disabled.

33.4.14 Timer counter reset

In order to reset the content of LPTIM_CNT register, two reset mechanisms are implemented:

• • The synchronous reset mechanism: the synchronous reset is controlled by the COUNTRST bit in the LPTIM_CR register. After setting the COUNTRST bitfield to '1', the reset signal is propagated in the LPTIM kernel clock domain. So it is important to note that a few clock pulses of the LPTIM kernel logic elapse before the reset is taken into account. This makes the LPTIM counter count few extra pluses between the time when the reset is triggered and it become effective. Since the COUNTRST bit is located in the APB clock domain and the LPTIM counter is located in the LPTIM kernel clock domain, a delay of 3 clock cycles of the kernel clock is needed to synchronize the reset signal issued by the APB clock domain when writing '1' to the COUNTRST bit.

Note: The software ensures that COUNRST bit is '0' before generating every synchronous reset.

• • The asynchronous reset mechanism: the asynchronous reset is controlled by the RSTARE bit located in the LPTIM_CR register. When this bit is set to '1', any read access to the LPTIM_CNT register resets its content to zero. Asynchronous reset must be triggered within a timeframe in which no LPTIM core clock is provided. For example when LPTIM Input1 is used as external clock source, the asynchronous reset must be applied only when there is enough insurance that no toggle occurs on the LPTIM Input1.

To read reliably the content of the LPTIM_CNT register two successive read accesses must be performed and compared. A read access can be considered reliable when the value of the two read accesses is equal. Unfortunately when asynchronous reset is enabled there is no possibility to read twice the LPTIM_CNT register.

Warning: There is no mechanism inside the LPTIM that prevents the two reset mechanisms from being used simultaneously. The developer must make sure that these two mechanisms are used exclusively.

33.4.15 Encoder mode

This mode allows handling signals from quadrature encoders used to detect angular position of rotary elements. Encoder interface mode acts simply as an external clock with direction selection. This means that the counter just counts continuously between 0 and the auto-reload value programmed into the LPTIM_ARR register (0 up to ARR or ARR down to 0 depending on the direction). Therefore LPTIM_ARR must be configured before starting the counter. From the two external input signals, Input1 and Input2, a clock signal is generated to clock the LPTIM counter. The phase between those two signals determines the counting direction.

The Encoder mode is only available when the LPTIM is clocked by an internal clock source. The signals frequency on both Input1 and Input2 inputs must not exceed the LPTIM internal clock frequency divided by 4. This is mandatory in order to guarantee a proper operation of the LPTIM.

Direction change is signalized by the two down and up flags in the LPTIM_ISR register. An interrupt can be generated for both direction change events if enabled through the DOWNIE bit.

To activate the Encoder mode the ENC bit has to be set to 1. The LPTIM must first be configured in Continuous mode.

When Encoder mode is active, the LPTIM counter is modified automatically following the speed and the direction of the incremental encoder. Therefore, its content always represents the encoder's position. The count direction, signaled by the Up and Down flags, correspond to the rotation direction of the encoder rotor.

According to the edge sensitivity configured using the CKPOL[1:0] bits, different counting scenarios are possible. The following table summarizes the possible combinations, assuming that Input1 and Input2 do not switch at the same time.

Table 331. Encoder counting scenarios

The following figure shows a counting sequence for Encoder mode where both-edge sensitivity is configured.

Caution: In this mode the LPTIM must be clocked by an internal clock source, so the CKSEL bit must be maintained to its reset value which is equal to 0. Also, the prescaler division ratio must be equal to its reset value which is 1 (PRESC[2:0] bits must be 000).

Figure 370. Encoder mode counting sequence

33.4.16 Repetition counter

The LPTIM features a repetition counter that decrements by 1 each time an LPTIM counter overflow event occurs. A repetition counter underflow event is generated when the repetition counter contains zero and the LPTIM counter overflows. Next to each repetition counter underflow event, the repetition counter gets loaded with the content of the REP[7:0] bitfield which belongs to the repetition register LPTIM_RCR.

A repetition underflow event is generated on each and every LPTIM counter overflow when the REP[7:0] register is set to 0.

When PRELOAD = 1, writing to the REP[7:0] bitfield has no effect on the content of the repetition counter until the next repetition underflow event occurs. The repetition counter continues to decrement each LPTIM counter overflow event and only when a repetition underflow event is generated, the new value written into REP[7:0] is loaded into the repetition counter. This behavior is depicted in Figure 371 .

Figure 371. Continuous counting mode when repetition register LPTIM_RCR different from zero (with PRELOAD = 1)

A repetition counter underflow event is systematically associated with LPTIM preloaded registers update (refer to Section 33.4.11: Register update for more information).

Repetition counter underflow event is signaled to the software through the update event (UE) flag mapped into the LPTIM_ISR register. When set, the UE flag can trigger an LPTIM interrupt if its respective update event interrupt enable (UEIE) control bit, mapped to the LPTIM_DIER register, is set.

The repetition register LPTIM_RCR is located in the APB bus interface clock domain where the repetition counter itself is located in the LPTIM kernel clock domain. Each time a new value is written to the LPTIM_RCR register, this new content is propagated from the APB bus interface clock domain to the LPTIM kernel clock domain. The new written value is then loaded to the repetition counter immediately after a repetition counter underflow event. The synchronization delay for the new written content is four APB clock cycles plus three LPTIM kernel clock cycles and it is signaled by the REPOK flag located in the LPTIM_ISR register when it is elapsed. When the LPTIM kernel clock cycle is relatively slow, for instance when the LPTIM kernel is being clocked by the LSI clock source, it can be lengthy to keep polling on the REPOK flag by software to detect that the synchronization of the LPTIM_RCR register content is finished. For that reason, the REPOK flag, when set, can generate an interrupt if its associated REPOKIE control bit in the LPTIM_DIER register is set.

Note: After a write to the LPTIM_RCR register, a new write operation to the same register can only be performed when the previous write operation is completed. Any successive writes before the REPOK flag is set, lead to unpredictable results.

Caution: When using repetition counter with PRELOAD = 0, LPTIM_RCR register must be changed at least five counter cycles before the autoreload match event, otherwise an unpredictable behavior may occur.

33.4.17 Capture/compare channels

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

Input stage

The input stage samples the corresponding LPTIx input to generate a filtered signal LPTIxF. Then, an edge detector with polarity selection generates ICx signal used as the capture command. It is prescaled to generate the capture command signal (ICxPS).

Figure 372. Capture/compare input stage (channel 1)

Output stage

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

Figure 373. Capture/compare output stage (channel 1)

33.4.18 Input capture mode

In Input capture mode, the capture/compare registers (LPTIM_CCRx) are used to latch the value of the counter after a transition detected by the corresponding ICx signal. Assuming input capture is enabled on a channel x (CCxE set) and when a capture occurs, the corresponding CCxIF flag (LPTIM_ISR 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 over-capture flag CCxOF (LPTIM_ISR register) is set. CCxIF can be cleared by software by writing the CCxICF to 1 or by reading the captured data stored in the LPTIM_CCRx register. CCxOF is cleared by writing CCxOCF to 1.

Note: In DMA mode, the input capture channel have to be enabled (set CCxE bit) the last, after enabling the DMA request and after starting the counter. This is in order to prevent generating an input capture DMA request when the counter is not started yet.

Input capture Glitch filter latency

When a trigger event arrives on channel x input (LPTIx) and depending on the configured glitch filter (ICxF[1:0] field in CCMRx register) and on the kernel clock prescaler value (PRESC[2:0] field in CFGR register), there is a variable latency that leads to a systematic offset (see Table 332 ) between the captured value stored in the CCRx register and the real value corresponding to the capture trigger.

This offset has no impact on pulse width measurement as it is systematic and compensated between two captures.

The real capture value corresponding to the input capture trigger can be calculated using the below formula:

Real capture value = captured(LPTIM_CCRx) - offset

The relevant offset must be used depending on the glitch filter and on the kernel clock prescaler value (PRESC field in CFGR register)

Example: determining the real capture value when PRESC[2:0] = 0x2 and ICxF = 0x3. For this configuration (PRESC[2:0] = 0x2 and ICxF = 0x3) and according to the Table 332 , the offset is 5.

Assuming that the captured value in CCRx is 9 (LPTIM_CNT = 9), this means that the capture trigger occurred when the LPTIM_CNT was equal to 9 - 5 = 4.

Table 332. Input capture Glitch filter latency (in counter step unit)

Table 332. Input capture Glitch filter latency (in counter step unit) (continued)

33.4.19 PWM mode

The PWM mode enables to generate a signal with a frequency determined by the value of the LPTIM_ARR register and a duty cycle determined by the value of the LPTIM_CCRx register. The LPTIM is able to generate PWM in edge-aligned mode.

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

Figure 374 gives an example where the LPTIM channel 1 is configured in PWM mode with LPTIM_CCR1 = 6 then 1 and LPTIM_ARR=10.

Figure 374. Edge-aligned PWM mode (PRELOAD = 1)

In the following example the reference PWM signal OCxREF is low as long as LPTIM_CNT ≤ LPTIM_CCRx else it becomes high.

Figure 375 shows some edge-aligned PWM waveforms in an example where LPTIM_ARR = 8.

Figure 375. Edge-aligned PWM waveforms (ARR=8 and CCxP = 0)

PWM mode with immediate update PRELOAD = 0

The PWM mode with PRELOAD = 0 enables the early change of the output level within the current PWM cycle. Based on the immediate update (PRELOAD = 0) of the LPTIM_CCRx register and on the continuous comparison of LPTIM_CNT and LPTIM_CCRx registers, it permits to have a new duty cycle value applied as soon as possible within the current PWM cycle, without having to wait for the completion of the current PWM period.

When the (PRELOAD = 0), the OCxREF signal level can be changed on-the-fly by software (or DMA) by updating the compare value in the LPTIM_CCRx register.

Depending on the written compare value and on the current counter and compare values, the OCxREF level is re-assigned as illustrated below:

• • If the new compare value does not exceed the current counter value and the current compare value exceeds the counter, OCxREF level is re-assigned high as soon as the new compare value is written.
• • If the new compare value exceeds the counter value and the current compare value does not exceed the counter, OCxREF level is re-assigned low as soon as the new compare value is written.

The output reference signal OCxREF level is left unchanged when none of the new compare value and the current compare value exceed the counter. Figure 376 illustrates the behavior of the OCxREF signal level when PRELOAD = 0 and PRELOAD = 1.

Figure 376. PWM mode with immediate update versus preloaded update

Note: For both PWM modes, the compare match, auto-reload match, and the update event flags are set one LPTIM counter cycle later after the corresponding event, the OCxREF level is also changed one LPTIM counter cycle later after the corresponding event. For instance when the LPTIM_CCRx is set to 3 the CCxIF is set when the LPTIM_CNT = 4. Figure 374 illustrates this behavior.

33.4.20 Autonomous mode

When clocked by oscillators available in this mode (refer to RCC), the LPTIM can operate in autonomous mode, remaining then fully functional in Stop mode where the APB clock is stopped. The APB clock is requested by the peripheral each time a data must be transferred from or to the SRAM. Once the APB clock is received by the peripheral, either an interrupt or a DMA request is generated, depending on the LPTIM configuration.

In order to offload the CPU (in Run mode) or to avoid to wake it up when in Stop mode, it is possible to use LPTIM DMA requests to transfer the captured values when in input capture mode or to update LPTIM registers when in PWM mode.

When in Stop mode, the LPTIM counter can be automatically started after the detection of an active edge on one of its external input triggers.

Input capture mode

To operate autonomously in Stop mode, the input capture DMA request must be enabled by setting the CCxDE bit in the LPTIM_DIER register.

Each time a counter value is captured and available in the LPTIM_CCRx register, the APB clock is requested by the peripheral and a DMA request is generated. The captured value is then transferred to the SRAM. The CCxIF flag is automatically cleared by hardware once the captured value is read by APB (can be any bus master like CPU or DMA).

PWM mode

The LPTIM can be configured to autonomously change, at each update event, the output waveform pulse width and/or the duty cycle without any CPU intervention. To enable this autonomous mode, the corresponding UEDE bit must be set in the LPTIM_DIER register.

At each update event, the APB clock is requested by the peripheral and a DMA request is generated. DMA direction must be configured as memory-to-peripheral which enables updating LPTIM registers, at each DMA request, with values stored in SRAM.

The UE flag is automatically cleared by hardware once the LPTIM_ARR register is written by any bus master like CPU or DMA. Thus, to enable automatic hardware clearing of UE flag, the application must configure the LPTIM_ARR register to be the last one to be written (at the end of list). For instance, if LPTIM_CCR1 and LPTIM_RCR registers need to be updated in Stop mode by DMA, the update sequence must be: LPTIM_CCR1, LPTIM_RCR then LPTIM_ARR.

The UE flag can also be cleared over its corresponding clear bit UECF in the LPTIM_ICR register, this can be done by configuring the DMA to write the LPTIM_ICR register at the end of register update.

33.4.21 DMA requests

The LPTIM can generate two categories of DMA requests:

• • DMA requests used to retrieve the input-capture counter values
• • DMA update requests used to re-program part of the LPTIM, multiple times, at regular intervals, without software overhead

Input capture DMA request

Each LPTIM channel has its dedicated input capture DMA request. A DMA request is generated (if CCxDE bit is set in LPTIM_DIER) and CCxIF is set each time a capture is ready in the LPTIM_CCRx register. The captured values in LPTIM_CCRx can then be transferred regularly by DMA to the desired memory destination. The CCxIF is automatically cleared by hardware when the captured value in LPTIM_CCRx register is read.

Note: The ICx DMA request signal lptim_icx_dma is reset in the following conditions:

• - if the corresponding DMA request is disabled (clear CCxDE bit in the LPTIM_DIER register)
• - or if the channel x is disabled (clear CCxE bit)
• - or if the LPTIM is disabled (clear the ENABLE bit in the LPTIM_CR register)

Update event DMA request

A DMA request is generated (if UEDE is set in LPTIM_DIER) and the UE flag is set at each update event. DMA request can be used to regularly update the LPTIM_ARR, the LPTIM_RCR or the LPTIM_CCRx registers permitting to generate custom PWM waveforms.

The UE is automatically cleared by hardware upon any bus master (like CPU or DMA) write access to the LPTIM_ARR register.

Note: The UE DMA request signal lptim_ue_dma is reset in the following conditions:

• - if the corresponding DMA request is disabled (clear UEDE bit in the LPTIM_DIER register)
• - or if the LPTIM is disabled (clear the ENABLE bit in the LPTIM_CR register)
• - or if the channel x is disabled (clear CCxE bit) and all the other channels are already disabled

33.4.22 Debug mode

When the microcontroller enters debug mode (core halted), the LPTIM counter either continues to work normally or stops, depending on the timer dedicated bit configuration in the debug support (DBG) peripheral.

For further details, refer to section debug support (DBG).

33.5 LPTIM low-power modes

Table 333. Effect of low-power modes on the LPTIM

33.6 LPTIM interrupts

The following events generate an interrupt/wake-up event, if they are enabled through the LPTIM_DIER register:

• • Compare match
• • Auto-reload match (whatever the direction if Encoder mode)
• • External trigger event
• • Autoreload register write completed
• • Compare register write completed
• • Direction change (Encoder mode), programmable (up / down / both).
• • Update Event
• • Repetition register update OK
• • Input capture occurred
• • Over-capture occurred
• • Interrupt enable register update OK

Note: If any bit in the LPTIM_DIER register is set after that its corresponding flag in the LPTIM_ISR register (status register) is set, the interrupt is not asserted.

Table 334. Interrupt events

1. 1. Each LPTIM event can wake up the device from Stop mode only if the LPTIM instance supports the wake-up from Stop mode feature. Refer to Section 33.3: LPTIM implementation .
2. 2. If LPTIM does not support Encoder mode feature, this event does not exist. Refer to Section 33.3: LPTIM implementation .

33.7 LPTIM registers

Refer to Section 1.2: List of abbreviations for registers on page 78 for a list of abbreviations used in register descriptions.

The peripheral registers can only be accessed by words (32-bit).

33.7.1 LPTIMx interrupt and status register [alternate] (LPTIMx_ISR) (x = 1, 2)

This description of the register can only be used for output compare mode. See next section for input capture mode.

Address offset: 0x000

Reset value: 0x0000 0000

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

Bit 24 DIEROK : Interrupt enable register update OK

DIEROK is set by hardware to inform application that the APB bus write operation to the LPTIM_DIER register has been successfully completed. DIEROK flag can be cleared by writing 1 to the DIEROKCF bit in the LPTIM_ICR register.

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

Bit 21 Reserved, must be kept at reset value.

Bit 20 Reserved, must be kept at reset value.

Bit 19 CMP2OK : Compare register 2 update OK

CMP2OK is set by hardware to inform application that the APB bus write operation to the LPTIM_CCR2 register has been successfully completed. CMP2OK flag can be cleared by writing 1 to the CMP2OKCF bit in the LPTIM_ICR register.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bits 18:12 Reserved, must be kept at reset value.

Bit 11 Reserved, must be kept at reset value.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC2IF : Compare 2 interrupt flag

If channel CC2 is configured as output:

The CC2IF flag is set by hardware to inform application that LPTIM_CNT register value matches the compare register's value. CC2IF flag can be cleared by writing 1 to the CC2CF bit in the LPTIM_ICR register.

0: No match

1: The content of the counter LPTIM_CNT register value has matched the LPTIM_CCR2 register's value

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 8 REPOK : Repetition register update OK

REPOK is set by hardware to inform application that the APB bus write operation to the LPTIM_RCR register has been successfully completed. REPOK flag can be cleared by writing 1 to the REPOKCF bit in the LPTIM_ICR register.

UE is set by hardware to inform application that an update event was generated. The corresponding interrupt or DMA request is generated if enabled. UE flag can be cleared by writing 1 to the UECF bit in the LPTIM_ICR register. The UE flag is automatically cleared by hardware once the LPTIM_ARR register is written by any bus master like CPU or DMA.

In Encoder mode, DOWN bit is set by hardware to inform application that the counter direction has changed from up to down. DOWN flag can be cleared by writing 1 to the DOWNCF bit in the LPTIM_ICR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3 .

In Encoder mode, UP bit is set by hardware to inform application that the counter direction has changed from down to up. UP flag can be cleared by writing 1 to the UP CF bit in the LPTIM_ICR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3 .

ARROK is set by hardware to inform application that the APB bus write operation to the LPTIM_ARR register has been successfully completed. ARROK flag can be cleared by writing 1 to the ARROKCF bit in the LPTIM_ICR register.

CMP1OK is set by hardware to inform application that the APB bus write operation to the LPTIM_CCR1 register has been successfully completed. CMP1OK flag can be cleared by writing 1 to the CMP1OKCF bit in the LPTIM_ICR register.

EXTTRIG is set by hardware to inform application that a valid edge on the selected external trigger input has occurred. If the trigger is ignored because the timer has already started, then this flag is not set. EXTTRIG flag can be cleared by writing 1 to the EXTTRIGCF bit in the LPTIM_ICR register.

ARRM is set by hardware to inform application that LPTIM_CNT register's value reached the LPTIM_ARR register's value. ARRM flag can be cleared by writing 1 to the ARRMCF bit in the LPTIM_ICR register.

The CC1IF flag is set by hardware to inform application that LPTIM_CNT register value matches the compare register's value. CC1IF flag can be cleared by writing 1 to the CC1CF bit in the LPTIM_ICR register.

0: No match

1: The content of the counter LPTIM_CNT register value has matched the LPTIM_CCR1 register's value

33.7.2 LPTIMx interrupt and status register [alternate] (LPTIMx_ISR)
(x = 1, 2)

This description of the register can only be used for input capture mode. See previous section for output compare mode.

Address offset: 0x000

Reset value: 0x0000 0000

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

Bit 24 DIEROK : Interrupt enable register update OK

DIEROK is set by hardware to inform application that the APB bus write operation to the LPTIM_DIER register has been successfully completed. DIEROK flag can be cleared by writing 1 to the DIEROKCF bit in the LPTIM_ICR register.

Bits 23:16 Reserved, must be kept at reset value.

Bit 15 Reserved, must be kept at reset value.

Bit 14 Reserved, must be kept at reset value.

Bit 13 CC2OF : Capture 2 over-capture 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 1 to the CC2OCF bit in the LPTIM_ICR register.

0: No over-capture has been detected.

1: The counter value has been captured in LPTIM_CCR2 register while CC2IF flag was already set.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 12 CC1OF : Capture 1 over-capture 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 1 to the CC1OCF bit in the LPTIM_ICR register.

0: No over-capture has been detected.

1: The counter value has been captured in LPTIM_CCR1 register while CC1IF flag was already set.

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bit 11 Reserved, must be kept at reset value.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC2IF : Capture 2 interrupt flag

If channel CC2 is configured as input:

CC2IF is set by hardware to inform application that the current value of the counter is captured in LPTIM_CCR2 register. The corresponding interrupt or DMA request is generated if enabled. The CC2OF flag is set if the CC2IF flag was already high.

0: No input capture occurred

1: The counter value has been captured in the LPTIM_CCR2 register. (An edge has been detected on IC2 which matches the selected polarity). The CC2IF flag is automatically cleared by hardware once the captured value is read (CPU or DMA). The CC2IF flag can be cleared by writing 1 to the CC2CF bit in the LPTIM_ICR register.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 8 REPOK : Repetition register update OK

REPOK is set by hardware to inform application that the APB bus write operation to the LPTIM_RCR register has been successfully completed. REPOK flag can be cleared by writing 1 to the REPOKCF bit in the LPTIM_ICR register.

Bit 7 UE : LPTIM update event occurred

UE is set by hardware to inform application that an update event was generated. The corresponding interrupt or DMA request is generated if enabled. The UE flag can be cleared by writing 1 to the UECF bit in the LPTIM_ICR register. The UE flag is automatically cleared by hardware once the LPTIM_ARR register is written by any bus master like CPU or DMA.

Bit 6 DOWN : Counter direction change up to down

In Encoder mode, DOWN bit is set by hardware to inform application that the counter direction has changed from up to down. DOWN flag can be cleared by writing 1 to the DOWNCF bit in the LPTIM_ICR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 5 UP : Counter direction change down to up

In Encoder mode, UP bit is set by hardware to inform application that the counter direction has changed from down to up. UP flag can be cleared by writing 1 to the UPCF bit in the LPTIM_ICR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 4 ARROK : Autoreload register update OK

ARROK is set by hardware to inform application that the APB bus write operation to the LPTIM_ARR register has been successfully completed. ARROK flag can be cleared by writing 1 to the ARROKCF bit in the LPTIM_ICR register.

Bit 3 Reserved, must be kept at reset value.

Bit 2 EXTTRIG : External trigger edge event

EXTTRIG is set by hardware to inform application that a valid edge on the selected external trigger input has occurred. If the trigger is ignored because the timer has already started, then this flag is not set. EXTTRIG flag can be cleared by writing 1 to the EXTTRIGCF bit in the LPTIM_ICR register.

Bit 1 ARRM : Autoreload match

ARRM is set by hardware to inform application that LPTIM_CNT register's value reached the LPTIM_ARR register's value. ARRM flag can be cleared by writing 1 to the ARRMCF bit in the LPTIM_ICR register.

Bit 0 CC1IF : capture 1 interrupt flag

If channel CC1 is configured as input:

CC1IF is set by hardware to inform application that the current value of the counter is captured in LPTIM_CCR1 register. The corresponding interrupt or DMA request is generated if enabled. The CC1OF flag is set if the CC1IF flag was already high.

0: No input capture occurred

1: The counter value has been captured in the LPTIM_CCR1 register. (An edge has been detected on IC1 which matches the selected polarity). The CC1IF flag is automatically cleared by hardware once the captured value is read (CPU or DMA). CC1IF flag can be cleared by writing 1 to the CC1CF bit in the LPTIM_ICR register.

33.7.3 LPTIMx interrupt clear register [alternate] (LPTIMx_ICR)
(x = 1, 2)

This description of the register can only be used for output compare mode. See next section for input capture compare mode.

Address offset: 0x004

Reset value: 0x0000 0000

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

Bit 24 DIEROKCF : Interrupt enable register update OK clear flag

Writing 1 to this bit clears the DIEROK flag in the LPTIM_ISR register.

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

Bit 21 Reserved, must be kept at reset value.

Bit 20 Reserved, must be kept at reset value.

Bit 19 CMP2OKCF : Compare register 2 update OK clear flag

Writing 1 to this bit clears the CMP2OK flag in the LPTIM_ISR register.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bits 18:12 Reserved, must be kept at reset value.

• Bit 11 Reserved, must be kept at reset value.
• Bit 10 Reserved, must be kept at reset value.
• Bit 9 CC2CF : Capture/compare 2 clear flag
  Writing 1 to this bit clears the CC2IF flag in the LPTIM_ISR register.
  Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.
• Bit 8 REPOKCF : Repetition register update OK clear flag
  Writing 1 to this bit clears the REPOK flag in the LPTIM_ISR register.
• Bit 7 UECF : Update event clear flag
  Writing 1 to this bit clear the UE flag in the LPTIM_ISR register.
• Bit 6 DOWNCF : Direction change to down clear flag
  Writing 1 to this bit clear the DOWN flag in the LPTIM_ISR register.
  Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.
• Bit 5 UPCF : Direction change to UP clear flag
  Writing 1 to this bit clear the UP flag in the LPTIM_ISR register.
  Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.
• Bit 4 ARROKCF : Autoreload register update OK clear flag
  Writing 1 to this bit clears the ARROK flag in the LPTIM_ISR register
• Bit 3 CMP1OKCF : Compare register 1 update OK clear flag
  Writing 1 to this bit clears the CMP1OK flag in the LPTIM_ISR register.
• Bit 2 EXTTRIGCF : External trigger valid edge clear flag
  Writing 1 to this bit clears the EXTTRIG flag in the LPTIM_ISR register
• Bit 1 ARRMCF : Autoreload match clear flag
  Writing 1 to this bit clears the ARRM flag in the LPTIM_ISR register
• Bit 0 CC1CF : Capture/compare 1 clear flag
  Writing 1 to this bit clears the CC1IF flag in the LPTIM_ISR register.

33.7.4 LPTIMx interrupt clear register [alternate] (LPTIMx_ICR) (x = 1, 2)

This description of the register can only be used for input capture mode. See previous section for output compare mode.

Address offset: 0x004

Reset value: 0x0000 0000

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

Bit 24 DIEROKCF : Interrupt enable register update OK clear flag

Writing 1 to this bit clears the DIEROK flag in the LPTIM_ISR register.

Bits 23:16 Reserved, must be kept at reset value.

Bit 15 Reserved, must be kept at reset value.

Bit 14 Reserved, must be kept at reset value.

Bit 13 CC2OCF : Capture/compare 2 over-capture clear flag

Writing 1 to this bit clears the CC2OF flag in the LPTIM_ISR register.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 12 CC1OCF : Capture/compare 1 over-capture clear flag

Writing 1 to this bit clears the CC1OF flag in the LPTIM_ISR register.

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bit 11 Reserved, must be kept at reset value.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC2CF : Capture/compare 2 clear flag

Writing 1 to this bit clears the CC2IF flag in the LPTIM_ISR register.

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 8 REPOKCF : Repetition register update OK clear flag

Writing 1 to this bit clears the REPOK flag in the LPTIM_ISR register.

Bit 7 UECF : Update event clear flag

Writing 1 to this bit clear the UE flag in the LPTIM_ISR register.

Bit 6 DOWNCF : Direction change to down clear flag

Writing 1 to this bit clear the DOWN flag in the LPTIM_ISR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 5 UPCF : Direction change to UP clear flag

Writing 1 to this bit clear the UP flag in the LPTIM_ISR register.

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 4 ARROKCF : Autoreload register update OK clear flag

Writing 1 to this bit clears the ARROK flag in the LPTIM_ISR register

Bit 3 Reserved, must be kept at reset value.

Bit 2 EXTTRIGCF : External trigger valid edge clear flag

Writing 1 to this bit clears the EXTTRIG flag in the LPTIM_ISR register

Bit 1 ARRMCF : Autoreload match clear flag

Writing 1 to this bit clears the ARRM flag in the LPTIM_ISR register

Bit 0 CC1CF : Capture/compare 1 clear flag

Writing 1 to this bit clears the CC1IF flag in the LPTIM_ISR register.

33.7.5 LPTIMx interrupt enable register [alternate] (LPTIMx_DIER) (x = 1, 2)

This description of the register can only be used for output compare mode. See next section for input capture compare mode.

Address offset: 0x008

Reset value: 0x0000 0000

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

Bit 23 UEDE : Update event DMA request enable

0: UE DMA request disabled. Writing '0' to the UEDE bit resets the associated ue_dma_req signal.

1: UE DMA request enabled

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bit 22 Reserved, must be kept at reset value.

Bit 21 Reserved, must be kept at reset value.

Bit 20 Reserved, must be kept at reset value.

Bit 19 CMP2OKIE : Compare register 2 update OK interrupt enable

0: CMPOK register 2 interrupt disabled

1: CMPOK register 2 interrupt enabled

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bits 18:12 Reserved, must be kept at reset value.

Bit 11 Reserved, must be kept at reset value.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC2IE : Capture/compare 2 interrupt enable

0: Capture/compare 2 interrupt disabled

1: Capture/compare 2 interrupt enabled

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 8 REPOKIE : Repetition register update OK interrupt Enable

0: Repetition register update OK interrupt disabled

1: Repetition register update OK interrupt enabled

Bit 7 UEIE : Update event interrupt enable

0: Update event interrupt disabled

1: Update event interrupt enabled

Bit 6 DOWNIE : Direction change to down Interrupt Enable

0: DOWN interrupt disabled

1: DOWN interrupt enabled

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 5 UPIE : Direction change to UP Interrupt Enable

0: UP interrupt disabled

1: UP interrupt enabled

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 4 ARROKIE : Autoreload register update OK Interrupt Enable

0: ARROK interrupt disabled

1: ARROK interrupt enabled

Bit 3 CMP1OKIE : Compare register 1 update OK interrupt enable

0: CMPOK register 1 interrupt disabled

1: CMPOK register 1 interrupt enabled

Bit 2 EXTTRIGIE : External trigger valid edge Interrupt Enable

0: EXTTRIG interrupt disabled

1: EXTTRIG interrupt enabled

Bit 1 ARRMIE : Autoreload match Interrupt Enable

0: ARRM interrupt disabled

1: ARRM interrupt enabled

Bit 0 CC1IE : Capture/compare 1 interrupt enable

0: Capture/compare 1 interrupt disabled

1: Capture/compare 1 interrupt enabled

33.7.6 LPTIMx interrupt enable register [alternate] (LPTIMx_DIER) (x = 1, 2)

This description of the register can only be used for input capture mode. See previous section for output compare mode.

Address offset: 0x008

Reset value: 0x0000 0000

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

Bit 27 Reserved, must be kept at reset value.

Bit 26 Reserved, must be kept at reset value.

Bit 25 CC2DE : Capture/compare 2 DMA request enable

0: CC2 DMA request disabled. Writing '0' to the CC2DE bit resets the associated ic2_dma_req signal.

1: CC2 DMA request enabled

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 24 Reserved, must be kept at reset value.

Bit 23 UEDE : Update event DMA request enable

0: UE DMA request disabled. Writing '0' to the UEDE bit resets the associated ue_dma_req signal.

1: UE DMA request enabled

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bits 22:17 Reserved, must be kept at reset value.

Bit 16 CC1DE : Capture/compare 1 DMA request enable

0: CC1 DMA request disabled. Writing '0' to the CC1DE bit resets the associated ic1_dma_req signal.

1: CC1 DMA request enabled

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bit 15 Reserved, must be kept at reset value.

Bit 14 Reserved, must be kept at reset value.

Bit 13 CC2OIE : Capture/compare 2 over-capture interrupt enable

0: CC2 over-capture interrupt disabled

1: CC2 over-capture interrupt enabled

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 12 CC1OIE : Capture/compare 1 over-capture interrupt enable

0: CC1 over-capture interrupt disabled

1: CC1 over-capture interrupt enabled

Note: If LPTIM does not implement at least 1 channel this bit is reserved. Refer to Section 33.3.

Bit 11 Reserved, must be kept at reset value.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CC2IE : Capture/compare 2 interrupt enable

0: Capture/compare 2 interrupt disabled

1: Capture/compare 2 interrupt enabled

Note: If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3.

Bit 8 REPOKIE : Repetition register update OK interrupt Enable

0: Repetition register update OK interrupt disabled

1: Repetition register update OK interrupt enabled

Bit 7 UEIE : Update event interrupt enable

0: Update event interrupt disabled

1: Update event interrupt enabled

Bit 6 DOWNIE : Direction change to down Interrupt Enable

0: DOWN interrupt disabled

1: DOWN interrupt enabled

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3.

Bit 5 UPIE : Direction change to UP Interrupt Enable

0: UP interrupt disabled

1: UP interrupt enabled

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3 .

Bit 4 ARROKIE : Autoreload register update OK Interrupt Enable

0: ARROK interrupt disabled

1: ARROK interrupt enabled

Bit 3 Reserved, must be kept at reset value.

Bit 2 EXTTRIGIE : External trigger valid edge Interrupt Enable

0: EXTTRIG interrupt disabled

1: EXTTRIG interrupt enabled

Bit 1 ARRMIE : Autoreload match Interrupt Enable

0: ARRM interrupt disabled

1: ARRM interrupt enabled

Bit 0 CC1IE : Capture/compare 1 interrupt enable

0: Capture/compare 1 interrupt disabled

1: Capture/compare 1 interrupt enabled

33.7.7 LPTIM configuration register (LPTIM_CFGR)

Address offset: 0x00C

Reset value: 0x0000 0000

Bits 31:30 Reserved, must be kept at reset value.

Bit 29 Reserved, must be kept at reset value.

Bits 28:25 Reserved, must be kept at reset value.

Bit 24 ENC : Encoder mode enable

The ENC bit controls the Encoder mode

0: Encoder mode disabled

1: Encoder mode enabled

Note: If the LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3 .

Bit 23 COUNTMODE : counter mode enabled

The COUNTMODE bit selects which clock source is used by the LPTIM to clock the counter:

0: The counter is incremented following each internal clock pulse

1: The counter is incremented following each valid clock pulse on the LPTIM external Input1

Bit 22 PRELOAD : Registers update mode

The PRELOAD bit controls the LPTIM_ARR, LPTIM_RCR and the LPTIM_CCRx registers update modality

0: Registers are updated after each APB bus write access

1: Registers are updated at the end of the current LPTIM period

Bit 21 Reserved, must be kept at reset value.

Bit 20 WAVE : Waveform shape

The WAVE bit controls the output shape

0: Deactivate Set-once mode

1: Activate the Set-once mode

Bit 19 TIMOUT : Timeout enable

The TIMOUT bit controls the Timeout feature

0: A trigger event arriving when the timer is already started is ignored

1: A trigger event arriving when the timer is already started resets and restarts the LPTIM counter and the repetition counter

Bits 18:17 TRIGEN[1:0] : Trigger enable and polarity

The TRIGEN bits controls whether the LPTIM counter is started by an external trigger or not. If the external trigger option is selected, three configurations are possible for the trigger active edge:

00: Software trigger (counting start is initiated by software)

01: Rising edge is the active edge

10: Falling edge is the active edge

11: Both edges are active edges

Bit 16 Reserved, must be kept at reset value.

Bits 15:13 TRIGSEL[2:0] : Trigger selector

The TRIGSEL bits select the trigger source that serves as a trigger event for the LPTIM among the below 8 available sources:

000: lptim_ext_trig0

001: lptim_ext_trig1

010: lptim_ext_trig2

011: lptim_ext_trig3

100: lptim_ext_trig4

101: lptim_ext_trig5

110: lptim_ext_trig6

111: lptim_ext_trig7

See Section 33.4.3: LPTIM input and trigger mapping for details.

Bit 12 Reserved, must be kept at reset value.

Bits 11:9 PRESC[2:0] : Clock prescaler

The PRESC bits configure the prescaler division factor. It can be one among the following division factors:

000: /1

001: /2

010: /4

011: /8

100: /16

101: /32

110: /64

111: /128

Bit 8 Reserved, must be kept at reset value.

The TRGFLT value sets the number of consecutive equal samples that are detected when a level change occurs on an internal trigger before it is considered as a valid level transition. An internal clock source must be present to use this feature

00: Any trigger active level change is considered as a valid trigger

01: Trigger active level change must be stable for at least 2 clock periods before it is considered as valid trigger.

10: Trigger active level change must be stable for at least 4 clock periods before it is considered as valid trigger.

11: Trigger active level change must be stable for at least 8 clock periods before it is considered as valid trigger.

Bit 5 Reserved, must be kept at reset value.

The CKFLT value sets the number of consecutive equal samples that are detected when a level change occurs on an external clock signal before it is considered as a valid level transition. An internal clock source must be present to use this feature

00: Any external clock signal level change is considered as a valid transition

01: External clock signal level change must be stable for at least 2 clock periods before it is considered as valid transition.

10: External clock signal level change must be stable for at least 4 clock periods before it is considered as valid transition.

11: External clock signal level change must be stable for at least 8 clock periods before it is considered as valid transition.

When the LPTIM is clocked by an external clock source, CKPOL bits is used to configure the active edge or edges used by the counter:

00: The rising edge is the active edge used for counting.

If the LPTIM is configured in Encoder mode (ENC bit is set), the Encoder sub-mode 1 is active.

01: The falling edge is the active edge used for counting.

If the LPTIM is configured in Encoder mode (ENC bit is set), the Encoder sub-mode 2 is active.

10: Both edges are active edges. When both external clock signal edges are considered active ones, the LPTIM must also be clocked by an internal clock source with a frequency equal to at least four times the external clock frequency.

If the LPTIM is configured in Encoder mode (ENC bit is set), the Encoder sub-mode 3 is active.

11: Not allowed

Refer to Section 33.4.15: Encoder mode for more details about Encoder sub-modes.

The CKSEL bit selects which clock source the LPTIM uses:

0: LPTIM is clocked by internal clock source (APB clock or any of the embedded oscillators)

1: LPTIM is clocked by an external clock source through the LPTIM external Input1

Caution: The LPTIM_CFGR register must only be modified when the LPTIM is disabled (ENABLE bit reset to 0).

33.7.8 LPTIM control register (LPTIM_CR)

Address offset: 0x010

Reset value: 0x0000 0000

Bits 31:5 Reserved, must be kept at reset value.

Bit 4 RSTARE : Reset after read enable

This bit is set and cleared by software. When RSTARE is set to '1', any read access to LPTIM_CNT register asynchronously resets LPTIM_CNT register content.

This bit can be set only when the LPTIM is enabled.

Bit 3 COUNTRST : Counter reset

This bit is set by software and cleared by hardware. When set to '1' this bit triggers a synchronous reset of the LPTIM_CNT counter register. Due to the synchronous nature of this reset, it only takes place after a synchronization delay of 3 LPTimer core clock cycles (LPTimer core clock can be different from APB clock).

This bit can be set only when the LPTIM is enabled. It is automatically reset by hardware.

Caution: COUNTRST must never be set to '1' by software before it is already cleared to '0' by hardware. Software must consequently check that COUNTRST bit is already cleared to '0' before attempting to set it to '1'.

Bit 2 CNTSTRT : Timer start in Continuous mode

This bit is set by software and cleared by hardware.

In case of software start (TRIGEN[1:0] = 00), setting this bit starts the LPTIM in Continuous mode.

If the software start is disabled (TRIGEN[1:0] different than 00), setting this bit starts the timer in Continuous mode as soon as an external trigger is detected.

If this bit is set when a single pulse mode counting is ongoing, then the timer does not stop at the next match between the LPTIM_ARR and LPTIM_CNT registers and the LPTIM counter keeps counting in Continuous mode.

This bit can be set only when the LPTIM is enabled. It is automatically reset by hardware.

Bit 1 SNGSTRT : LPTIM start in Single mode

This bit is set by software and cleared by hardware.

In case of software start (TRIGEN[1:0] = 00), setting this bit starts the LPTIM in single pulse mode.

If the software start is disabled (TRIGEN[1:0] different than 00), setting this bit starts the LPTIM in single pulse mode as soon as an external trigger is detected.

If this bit is set when the LPTIM is in continuous counting mode, then the LPTIM stops at the following match between LPTIM_ARR and LPTIM_CNT registers.

This bit can only be set when the LPTIM is enabled. It is automatically reset by hardware.

Bit 0 ENABLE : LPTIM enable

The ENABLE bit is set and cleared by software.

0: LPTIM is disabled. Writing '0' to the ENABLE bit resets all the DMA request signals (input capture and update event DMA requests).

1: LPTIM is enabled

33.7.9 LPTIM compare register 1 (LPTIM_CCR1)

Address offset: 0x014

Reset value: 0x0000 0000

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

Bits 15:0 CCR1[15:0] : Capture/compare 1 value

If channel CC1 is configured as output:

CCR1 is the value to be loaded in the capture/compare 1 register.

Depending on the PRELOAD option, the CCR1 register is immediately updated if the PRELOAD bit is reset and updated at next LPTIM update event if PRELOAD bit is reset.

The capture/compare register 1 contains the value to be compared to the counter LPTIM_CNT and signaled on OC1 output.

If channel CC1 is configured as input:

CCR1 becomes read-only, it contains the counter value transferred by the last input capture 1 event.

The LPTIM_CCR1 register is read-only and cannot be programmed.

Caution: The LPTIM_CCR1 register must only be modified when the LPTIM is enabled (ENABLE bit set to 1).

33.7.10 LPTIM autoreload register (LPTIM_ARR)

Address offset: 0x018

Reset value: 0x0000 0001

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

Bits 15:0 ARR[15:0] : Auto reload value

ARR is the autoreload value for the LPTIM.

This value must be strictly greater than the CCRx[15:0] value.

Caution: The LPTIM_ARR register must only be modified when the LPTIM is enabled (ENABLE bit set to 1).

33.7.11 LPTIM counter register (LPTIM_CNT)

Address offset: 0x01C

Reset value: 0x0000 0000

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

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

When the LPTIM is running, reading the LPTIM_CNT register may return unreliable values. In this case it is necessary to perform consecutive reads until two returned values are identical.

33.7.12 LPTIM configuration register 2 (LPTIM_CFGR2)

Address offset: 0x024

Reset value: 0x0000 0000

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

Bits 21:20 IC2SEL[1:0] : LPTIM input capture 2 selection

The IC2SEL bits control the LPTIM Input capture 2 multiplexer, which connects LPTIM Input capture 2 to one of the available inputs.

• 00: lptim_ic2_mux0
• 01: lptim_ic2_mux1
• 10: lptim_ic2_mux2
• 11: lptim_ic2_mux3

For connection details refer to Section 33.4.3: LPTIM input and trigger mapping .

Bits 19:18 Reserved, must be kept at reset value.

Bits 17:16 IC1SEL[1:0] : LPTIM input capture 1 selection

The IC1SEL bits control the LPTIM Input capture 1 multiplexer, which connects LPTIM Input capture 1 to one of the available inputs.

• 00: lptim_ic1_mux0
• 01: lptim_ic1_mux1
• 10: lptim_ic1_mux2
• 11: lptim_ic1_mux3

For connection details refer to Section 33.4.3: LPTIM input and trigger mapping .

Bits 15:6 Reserved, must be kept at reset value.

Bits 5:4 IN2SEL[1:0] : LPTIM input 2 selection

The IN2SEL bits control the LPTIM input 2 multiplexer, which connects LPTIM input 2 to one of the available inputs.

00: lptim_in2_mux0

01: lptim_in2_mux1

10: lptim_in2_mux2

11: lptim_in2_mux3

For connection details refer to Section 33.4.3: LPTIM input and trigger mapping .

Bits 3:2 Reserved, must be kept at reset value.

Bits 1:0 IN1SEL[1:0] : LPTIM input 1 selection

The IN1SEL bits control the LPTIM input 1 multiplexer, which connects LPTIM input 1 to one of the available inputs.

00: lptim_in1_mux0

01: lptim_in1_mux1

10: lptim_in1_mux2

11: lptim_in1_mux3

For connection details refer to Section 33.4.3: LPTIM input and trigger mapping .

33.7.13 LPTIM repetition register (LPTIM_RCR)

Address offset: 0x028

Reset value: 0x0000 0000

Bits 31:8 Reserved, must be kept at reset value.

Bits 7:0 REP[7:0] : Repetition register value

REP is the repetition value for the LPTIM.

Caution: The LPTIM_RCR register must only be modified when the LPTIM is enabled (ENABLE bit set to 1). When using repetition counter with PRELOAD = 0, LPTIM_RCR register must be changed at least five counter cycles before the auto reload match event, otherwise an unpredictable behavior may occur.

33.7.14 LPTIM capture/compare mode register 1 (LPTIM_CCMR1)

Address offset: 0x02C

Reset value: 0x0000 0000

The channels can be used in input (capture mode) or in output (PWM mode). The direction of a channel is defined by configuring the corresponding CCxSEL bits.

Bits 31:30 Reserved, must be kept at reset value.

Bits 29:28 IC2F[1:0] : Input capture 2 filter

This bitfield defines the number of consecutive equal samples that are detected when a level change occurs on an external input capture signal before it is considered as a valid level transition. An internal clock source must be present to use this feature.

00: Any external input capture signal level change is considered as a valid transition

01: External input capture signal level change must be stable for at least 2 clock periods before it is considered as valid transition.

10: External input capture signal level change must be stable for at least 4 clock periods before it is considered as valid transition.

11: External input capture signal level change must be stable for at least 8 clock periods before it is considered as valid transition.

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

Bits 25:24 IC2PSC[1:0] : Input capture 2 prescaler

This bitfield defines the ratio of the prescaler acting on the CC2 input (IC2).

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

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

Bits 19:18 CC2P[1:0] : Capture/compare 2 output polarity.

Condition: CC2 as output

Only bit2 is used to set polarity when output mode is enabled, bit3 is don't care.

0: OC2 active high

1: OC2 active low

Condition: CC2 as input

This field is used to select the IC2 polarity for capture operations.

00: Rising edge, circuit is sensitive to IC2 rising edge

01: Falling edge, circuit is sensitive to IC2 falling edge

10: Reserved, do not use this configuration.

11: Both edges, circuit is sensitive to both IC2 rising and falling edges.

Bit 17 CC2E : Capture/compare 2 output enable.

Condition: CC2 as output

0: Off - OC2 is not active. Writing '0' to the CC2E bit resets the ue_dma_req signal only if all the other LPTIM channels are disabled.

1: On - OC2 signal is output on the corresponding output pin

Condition: CC2 as input

This bit determines if a capture of the counter value can actually be done into the input capture/compare register 2 (LPTIM_CCR2) or not.

0: Capture disabled. Writing '0' to the CC2E bit resets the associated ic2_dma_req signal.

1: Capture enabled.

Bit 16 CC2SEL : Capture/compare 2 selection

This bitfield defines the direction of the channel, input (capture) or output mode.

0: CC2 channel is configured in output PWM mode

1: CC2 channel is configured in input capture mode

Bits 15:14 Reserved, must be kept at reset value.

Bits 13:12 IC1F[1:0] : Input capture 1 filter

This bitfield defines the number of consecutive equal samples that are detected when a level change occurs on an external input capture signal before it is considered as a valid level transition. An internal clock source must be present to use this feature.

00: Any external input capture signal level change is considered as a valid transition

01: External input capture signal level change must be stable for at least 2 clock periods before it is considered as valid transition.

10: External input capture signal level change must be stable for at least 4 clock periods before it is considered as valid transition.

11: External input capture signal level change must be stable for at least 8 clock periods before it is considered as valid transition.

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 IC1PSC[1:0] : Input capture 1 prescaler

This bitfield defines the ratio of the prescaler acting on the CC1 input (IC1).

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

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

Bits 3:2 CC1P[1:0] : Capture/compare 1 output polarity.

Condition: CC1 as output

Only bit2 is used to set polarity when output mode is enabled, bit3 is don't care.

0: OC1 active high, the LPTIM output reflects the compare results between LPTIM_ARR and LPTIM_CCRx registers

1: OC1 active low, the LPTIM output reflects the inverse of the compare results between LPTIM_ARR and LPTIM_CCRx registers

Condition: CC1 as input

This field is used to select the IC1 polarity for capture operations.

00: Rising edge, circuit is sensitive to IC1 rising edge

01: Falling edge, circuit is sensitive to IC1 falling edge

10: Reserved, do not use this configuration.

11: Both edges, circuit is sensitive to both IC1 rising and falling edges.

Bit 1 CC1E : Capture/compare 1 output enable.

Condition: CC1 as output

0: Off - OC1 is not active. Writing '0' to the CC1E bit resets the ue_dma_req signal only if all the other LPTIM channels are disabled.

1: On - OC1 signal is output on the corresponding output pin

Condition: CC1 as input

This bit determines if a capture of the counter value can actually be done into the input capture/compare register 1 (LPTIM_CCR1) or not.

0: Capture disabled. Writing '0' to the CC1E bit resets the associated ic1_dma_req signal.

1: Capture enabled.

Bit 0 CC1SEL : Capture/compare 1 selection

This bitfield defines the direction of the channel input (capture) or output mode.

0: CC1 channel is configured in output PWM mode

1: CC1 channel is configured in input capture mode

Caution: After a write to the LPTIM_CCMRx register, a new write operation to the same register can only be performed after a delay that must be equal or greater than the value of \( (\text{PRESC} \times 3) \) kernel clock cycles, PRESC[2:0] being the clock decimal division factor (1, 2, 4,..128). Any successive write violating this delay, leads to unpredictable results.

Caution: The CCxSEL, ICxF[1:0], CCxP[1:0] and ICxPSC[1:0] fields must only be modified when the channel x is disabled (CCxE bit reset to 0).

33.7.15 LPTIM compare register 2 (LPTIM_CCR2)

Address offset: 0x034

Reset value: 0x0000 0000

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

Bits 15:0 CCR2[15:0] : Capture/compare 2 value

If channel CC2 is configured as output:

CCR2 is the value to be loaded in the capture/compare 2 register.

Depending on the PRELOAD option, the CCR2 register is immediately updated if the PRELOAD bit is reset and updated at next LPTIM update event if PRELOAD bit is reset.

The capture/compare register 2 contains the value to be compared to the counter LPTIM_CNT and signaled on OC2 output.

If channel CC2 is configured as input:

CCR2 becomes read-only, it contains the counter value transferred by the last input capture 2 event. The LPTIM_CCR2 register is read-only and cannot be programmed.

Caution: The LPTIM_CCR2 register must only be modified when the LPTIM is enabled (ENABLE bit set to 1).

Note: If the LPTIM implements less than 2 channels this register is reserved. Refer to Section 33.3: LPTIM implementation .

33.7.16 LPTIM register map

The following table summarizes the LPTIM registers.

Table 335. LPTIM register map and reset values

Table 335. LPTIM register map and reset values (continued)

1. 1. If LPTIM does not implement at least 2 channels this bit is reserved. Refer to Section 33.3: LPTIM implementation .
2. 2. If LPTIM does not support Encoder mode feature, this bit is reserved. Refer to Section 33.3: LPTIM implementation .
3. 3. If the LPTIM implements less than 2 channels this register is reserved. Refer to Section 33.3: LPTIM implementation .

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