RM0367 Rev 7 579/1043
RM0367 General-purpose timers (TIM21/22)
601
Figure 186 gives an example of counter behavior when TI1FP1 polarity is inverted (same
configuration as above except CC1P=1).
Figure 186. Example of encoder interface mode with TI1FP1 polarity inverted
The timer, when configured in Encoder Interface mode provides information on the sensor’s
current position. Dynamic information can be obtained (speed, acceleration, deceleration)
by measuring the period between two encoder events using a second timer configured in
capture mode. The output of the encoder which indicates the mechanical zero can be used
for this purpose. Depending on the time between two events, the counter can also be read
at regular times. This can be done by latching the counter value into a third input capture
register if available (then the capture signal must be periodic and can be generated by
another timer). when available, it is also possible to read its value through a DMA request
generated by a Real-Time clock.
22.3.13 TIM21/22 external trigger synchronization
The TIM21/22 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.
Program CC1P and CC1NP to ‘00’ 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=’101’ in TIMx_SMCR register.
3. Start the counter by writing CEN=’1’ in the TIMx_CR1 register.
For code example, refer to A.11.12: Reset mode code example.
TI1
backwardjitter jitter
updown
TI2
Counter
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MS33108V1
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