General-purpose timer (TIMx) RM0008
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13.3.10 One pulse mode
One Pulse Mode (OPM) is a particular case of the previous modes. It allows the counter to
be started in response to a stimulus and to generate a pulse with a programmable length
after a programmable delay.
Starting the counter can be controlled through the slave mode controller. Generating the
waveform can be done in output compare mode or PWM mode. You select One Pulse Mode
by setting the OPM bit in the TIMx_CR1 register. This makes the counter stop automatically
at the next update event UEV.
A pulse can be correctly generated only if the compare value is different from the counter
initial value. Before starting (when the timer is waiting for the trigger), the configuration must
be:
In upcounting: CNT<CCRx≤ARR (in particular, 0<CCRx),
In downcounting: CNT>CCRx.
Figure 127. Example of one pulse mode.
For example you may want to generate a positive pulse on OC1 with a length of t
PULSE
and
after a delay of t
DELAY
as soon as a positive edge is detected on the TI2 input pin.
Let’s use TI2FP2 as trigger 1:
● Map TI2FP2 on TI2 by writing IC2S=’01’ in the TIMx_CCMR1 register.
● TI2FP2 must detect a rising edge, write CC2P=’0’ in the TIMx_CCER register.
● Configure TI2FP2 as trigger for the slave mode controller (TRGI) by writing TS=’110’ in
the TIMx_SMCR register.
● TI2FP2 is used to start the counter by writing SMS to ‘110’ in the TIMx_SMCR register
(trigger mode).
TI2
OC1REF
Counter
t
0
TIM1_ARR
TIM1_CCR1
OC1
t
DELAY
t
PULSE
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