Table 182. Counting Direction Versus Encoder Signals; Figure 225. Example Of Counter Operation In Encoder Interface Mode - ST STM32WL55JC Reference Manual

General-purpose timer (TIM2)
26.3.18 Timers and external trigger synchronization
The TIMx Timers can be synchronized with an external trigger in several modes: Reset
mode, Gated mode and Trigger mode.
Slave mode: Reset mode
The counter and its prescaler can be reinitialized in response to an event on a trigger input.
Moreover, if the URS bit from the TIMx_CR1 register is low, an update event UEV is
generated. Then all the preloaded registers (TIMx_ARR, TIMx_CCRx) are updated.
In the following example, the upcounter is cleared in response to a rising edge on TI1 input:
1. Configure the channel 1 to detect rising edges on 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 the TIMx_CCMR1 register. Write
CC1P=0 and CC1NP=0 in TIMx_CCER register to validate the polarity (and detect
rising edges only).
2. Configure the timer in reset mode by writing SMS=100 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=00101 in TIMx_SMCR register.
3. Start the counter by writing CEN=1 in the TIMx_CR1 register.
The counter starts counting on the internal clock, then behaves normally until TI1 rising
edge. When TI1 rises, the counter is cleared and restarts from 0. In the meantime, the
trigger flag is set (TIF bit in the TIMx_SR register) and an interrupt request can be sent if
enabled (depending on the TIE bit in TIMx_DIER register).
The following figure shows this behavior when the auto-reload register TIMx_ARR=0x36.
The delay between the rising edge on TI1 and the actual reset of the counter is due to the
resynchronization circuit on TI1 input.
Counter clock = ck_cnt = ck_psc
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 TI1 input is low:
858/1454
Figure 227. Control circuit in reset mode
TI1
UG
30
Counter register
TIF
RM0453 Rev 2
31 32 33 34 35 36 00 01 02 03 00 01 02 03
RM0453
MS31401V2