STM32W108HB datasheet(103/179 Pages) STMICROELECTRONICS

103 / 179 page

STM32W108CB, STM32W108HB

General-purpose timers

Doc ID 16252 Rev 2

103/179

8.1.13

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 TIM_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 TIM_IC1F = 0000. The capture

prescaler is not used for triggering, so it is not configured. The TIM_CC1S bits select

the input capture source only, TIM_CC1S = 01 in the TIMx_CCMR1 register. Write

TIM_CC1P = 0 in the TIMx_CCER register to validate the polarity, and detect rising

edges only.

●

Configure the timer in reset mode by writing TIM_SMS = 100 in the TIMx_SMCR

●

Start the counter by writing TIM_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 INT_TIMTIF bit in the INT_TIMxFLAG register) and an interrupt

request can be sent if enabled (depending on the INT_TIMTIF bit in the INT_TIMxCFG

Figure 36 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 36.

Control circuit in reset mode

Slave mode: gated mode

In gated mode the counter is enabled depending on the level of a selected input.

In the following example, the up-counter counts only when the TI1 input is low:

●

Configure channel 1 to detect low levels on TI1 Configure the input filter duration. In

this example, no filter is required, so TIM_IC1F = 0000. The capture prescaler is not

used for triggering, so it is not configured. The TIM_CC1S bits select the input capture

source only, TIM_CC1S = 01 in the TIMx_CCMR1 register. Write TIM_CC1P = 1 in the

TIMx_CCER register to validate the polarity (and detect low level only).

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