Figure 191. Ti2 External Clock Connection Example; Figure 192. Control Circuit In External Clock Mode 1 - ST STM32F405 Reference Manual

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For example, to configure the upcounter to count in response to a rising edge on the TI2

input, use the following procedure:

Configure channel 2 to detect rising edges on the TI2 input by writing CC2S = '01' in

the TIMx_CCMR1 register.

Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1

Select the rising edge polarity by writing CC2P='0' and CC2NP='0' in the TIMx_CCER

Configure the timer in external clock mode 1 by writing SMS='111' in the TIMx_SMCR

Select TI2 as the trigger input source by writing TS='110' in the TIMx_SMCR register.

Enable the counter by writing CEN='1' in the TIMx_CR1 register.

The capture prescaler is not used for triggering, so no need to configure it.

When a rising edge occurs on TI2, the counter counts once and the TIF flag is set.

The delay between the rising edge on TI2 and the actual clock of the counter is due to the

resynchronization circuit on TI2 input.

Counter clock = CK_CNT = CK_PSC

Figure 191. TI2 external clock connection example

TI2F_Falling

Counter register

General-purpose timers (TIM9 to TIM14)

Write TIF = 0

RM0090 Rev 18

External clock

Internal clock

(internal clock)

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