STM32W108CB datasheet(181/278 Pages) STMICROELECTRONICS

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STM32W108HB STM32W108CC STM32W108CB STM32W108CZ

General-purpose timers

Doc ID 16252 Rev 14

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10.1.13

Timers and external trigger synchronization

The timers can be synchronized with an external trigger in several modes: Reset mode,

Gated mode, and Trigger mode.

Slave mode: Reset mode

Reset mode reinitializes the counter and its prescaler in response to an event on a trigger

input. Moreover, if the URS bit in the TIMx_CR1 register is low, an update event is

generated. Then all the buffered registers (TIMx_ARR, TIMx_CCRy) are updated.

In the following example, the up-counter is cleared in response to a rising edge on the TI1

input:

●

Configure the channel 1 to detect rising edges on TI1: Configure the input filter

duration. In this example, no filter is required so IC1F = 0000. The capture prescaler is

not used for triggering, so it is not configured. The CC1S bits select the input capture

source only, CC1S = 01 in the TIMx_CCMR1 register. Write CC1P = 0 in the

TIMx_CCER register to validate the polarity, and detect rising edges only.

●

Configure the timer in Reset mode by writing SMS = 100 in the TIMx_SMCR register.

Select TI1 as the input source by writing TS = 101 in the TIMx_SMCR register.

●

Start the counter by writing CEN = 1 in the TIMx_CR1 register.

The counter starts counting on the internal clock, then behaves normally until the TI1 rising

edge. When TI1 rises, the counter is cleared and restarts from 0. In the meantime, the

trigger flag is set (the TIE bit in the TIMx_SR register) and an interrupt request can be sent if

enabled (depending on the TIE bit in the TIMx_IER register).

Figure 41 shows this behavior when the auto-reload register TIMx_ARR = 0x36. The delay

between the rising edge on TI1 and the actual reset of the counter is due to the

resynchronization circuit on the TI1 input.

Figure 41.

Control circuit in Reset mode

Counter clock = CK_CNT = CK_PSC

Counter register

01 02 03 00 01 02 03

32 33 34 35 36

TI1

TIE

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