Capture/Compare Channels; Figure 68. Control Circuit In External Clock Mode 2 - STMicroelectronics STM32F05 series Reference Manual

RM0091
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.
The delay between the rising edge on ETR and the actual clock of the counter is due to the
resynchronization circuit on the ETRP signal.

Figure 68. Control circuit in external clock mode 2

15.3.5

Capture/compare channels

Each Capture/Compare channel is built around a capture/compare register (including a
shadow register), a input stage for capture (with digital filter, multiplexing and prescaler) and
an output stage (with comparator and output control).
Figure 69
The input stage samples the corresponding TIx input to generate a filtered signal TIxF.
Then, an edge detector with polarity selection generates a signal (TIxFPx) which can be
used as trigger input by the slave mode controller or as the capture command. It is
prescaled before the capture register (ICxPS).
f
CNT_EN
Counter clock = CK_CNT = CK_PSC
Counter register
to Figure 72 give an overview of one Capture/Compare channel.
Doc ID 018940 Rev 1
CK_INT
ETR
ETRP
ETRF
34
Advanced-control timers (TIM1)
35 36
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