RM0090: Reference manual - STMicroelectronics

RM0090 General-purpose timers (TIM9 to TIM14)
Figure 186. Control circuit in gated mode
Slave mode: Trigger mode
TI1
cnt_en
Counter clock = ck_cnt = ck_psc
The counter can start in response to an event on a selected input.
In the following example, the upcounter starts in response to a rising edge on TI2 input:
1. Configure the channel 2 to detect rising edges on TI2. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC2F=’0000’). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC2S bits are
configured to select the input capture source only, CC2S=’01’ in TIMx_CCMR1 register.
Program CC2P=’1’ and CC2NP=’0’ in TIMx_CCER register to validate the polarity (and
detect low level only).
2. Configure the timer in trigger mode by writing SMS=’110’ in TIMx_SMCR register.
Select TI2 as the input source by writing TS=’110’ in TIMx_SMCR register.
When a rising edge occurs on TI2, the counter starts counting on the internal clock and the
TIF flag is set.
The delay between the rising edge on TI2 and the actual start of the counter is due to the
resynchronization circuit on TI2 input.
Figure 187. Control circuit in trigger mode
Counter register 30 31 32 33 34
35 36 37 38
TIF
TI2
cnt_en
Counter clock = ck_cnt = ck_psc
Write TIF=0
Counter register 34
35 36 37 38
TIF
Doc ID 018909 Rev 3 496/1416