Figure 156. Control Circuit In External Clock Mode 1; Figure 157. External Trigger Input Block - STMicroelectronics STM32F405 Reference Manual

Advanced arm-based 32-bit mcus

Table of Contents

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.

The counter can count at each rising or falling edge on the external trigger input ETR.

Figure 156. Control circuit in external clock mode 1

Counter clock = CK_CNT = CK_PSC

Counter register

gives an overview of the external trigger input block.

/1, /2, /4, /8

DocID018909 Rev 11

General-purpose timers (TIM2 to TIM5)

external clock

external clock

internal clock

(internal clock)

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