General-purpose timers (TIM15/TIM16/TIM17) RM0440
1386/2126 RM0440 Rev 4
Slave mode: Gated mode
The counter can be enabled depending on the level of a selected input.
In the following example, the upcounter counts only when tim_ti1 input is low:
1. Configure the channel 1 to detect low levels on tim_ti1. Configure the input filter
duration (in this example, we do not need any filter, so we keep IC1F=0000). The
capture prescaler is not used for triggering, so it does not need to be configured. The
CC1S bits select the input capture source only, CC1S=01 in TIMx_CCMR1 register.
Write CC1P=1 and CC1NP = ‘0’ in the TIMx_CCER register to validate the polarity (and
detect low level only).
2. Configure the timer in gated mode by writing SMS=101 in TIMx_SMCR register. Select
tim_ti1 as the input source by writing TS=00101 in TIMx_SMCR register.
3. Enable the counter by writing CEN=1 in the TIMx_CR1 register (in gated mode, the
counter doesn’t start if CEN=0, whatever is the trigger input level).
The counter starts counting on the internal clock as long as tim_ti1 is low and stops as soon
as tim_ti1 becomes high. The TIF flag in the TIMx_SR register is set both when the counter
starts or stops.
The delay between the rising edge on tim_ti1 and the actual stop of the counter is due to the
resynchronization circuit on tim_ti1 input.
Figure 477. Control circuit in gated mode
MSv62362V1
37
tim_cnt_ck, tim_psc_ck
Counter register
38
32 33
34
35 36
3130
TIF
tim_ti1
CEN
Write TIF = 0
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