Figure 180. Control Circuit In External Clock Mode 1; Figure 181. External Trigger Input Block - ST STM32F446 Series Reference Manual

RM0390
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 181
For example, to configure the upcounter to count each 2 rising edges on ETR, use the
following procedure:
1. As no filter is needed in this example, write ETF[3:0]=0000 in the TIMx_SMCR register.
2. Set the prescaler by writing ETPS[1:0]=01 in the TIMx_SMCR register
3. Select rising edge detection on the ETR pin by writing ETP=0 in the TIMx_SMCR
register
4. Enable external clock mode 2 by writing ECE=1 in the TIMx_SMCR register.
5. Enable the counter by writing CEN=1 in the TIMx_CR1 register.
The counter counts once each 2 ETR rising edges.

Figure 180. Control circuit in external clock mode 1

gives an overview of the external trigger input block.

Figure 181. External trigger input block

RM0390 Rev 4
General-purpose timers (TIM2 to TIM5)
535/1328
581