RM0008 General-purpose timers (TIM2 to TIM5)
Doc ID 13902 Rev 12 361/1096
Figure 121. 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:
For example, to configure the upcounter to count in response to a rising edge on the TI2
input, use the following procedure:
1. Configure channel 2 to detect rising edges on the TI2 input by writing CC2S= ‘01 in the
TIMx_CCMR1 register.
2. Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1
register (if no filter is needed, keep IC2F=0000).
Note: The capture prescaler is not used for triggering, so you don’t need to configure it.
3. Select rising edge polarity by writing CC2P=0 in the TIMx_CCER register.
4. Configure the timer in external clock mode 1 by writing SMS=111 in the TIMx_SMCR
register.
5. Select TI2 as the input source by writing TS=110 in the TIMx_SMCR register.
6. 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.
Figure 122. Control circuit in external clock mode 1
CK_INT
encoder
mode
external clock
mode 1
external clock
mode 2
internal clock
mode
ETRF
TRGI
TI1F
TI2F
or
or
or
(internal clock)
CK_PSC
ECE
TIMx_SMCR
SMS[2:0]
ITRx
TI1F_ED
TI1FP1
TI2FP2
ETRF
TIMx_SMCR
TS[2:0]
TI2
0
1
TIMx_CCER
CC2P
Filter
ICF[3:0]
TIMx_CCMR1
Edge
Detector
TI2F_Rising
TI2F_Falling
110
001
100
101
111
Counter clock = CK_CNT = CK_PSC
Counter register
35 3634
TI2
CNT_EN
TIF
Write TIF=0
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