Figure 140. Ti2 External Clock Connection Example; Figure 141. Control Circuit In External Clock Mode 1 - ST STM32F40 Series Reference Manual

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General-purpose timers (TIM2 to TIM5)

Figure 140. TI2 external clock connection example

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

The capture prescaler is not used for triggering, so you don't need to configure it.

Select 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 input source by writing TS=110 in the TIMx_SMCR register.

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

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.

External clock source mode 2

This mode is selected by writing ECE=1 in the TIMx_SMCR register.

TI2F_Falling

Counter clock = CK_CNT = CK_PSC

Counter register

Doc ID 018909 Rev 4

external clock

external clock

internal clock

(internal clock)

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