UM0306 General purpose timer (TIMx)
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Figure 104. 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).
The OPM waveform is defined by writing the compare registers (taking into account the
clock frequency and the counter prescaler).
● The t
DELAY
is defined by the value written in the TIMx_CCR1 register.
● The t
PULSE
is defined by the difference between the auto-reload value and the compare
value (TIMx_ARR - TIMx_CCR1).
● Let’s say you want to build a waveform with a transition from ‘0’ to ‘1’ when a compare
match occurs and a transition from ‘1’ to ‘0’ when the counter reaches the auto-reload
value. To do this you enable PWM mode 2 by writing OC1M=111 in the TIMx_CCMR1
register. You can optionally enable the preload registers by writing OC1PE=’1’ in the
TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this case you have to
write the compare value in the TIMx_CCR1 register, the auto-reload value in the
TIMx_ARR register, generate an update by setting the UG bit and wait for external
trigger event on TI2. CC1P is written to ‘0’ in this example.
In our example, the DIR and CMS bits in the TIMx_CR1 register should be low.
You only want 1 pulse, so you write ‘1’ in the OPM bit in the TIMx_CR1 register to stop the
counter at the next update event (when the counter rolls over from the auto-reload value
back to 0).
Particular case: OCx fast enable:
In One Pulse Mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
TI2
OC1Ref
COUNTER
t
0
TIM1_ARR
TIM1_CCR1
OC1
t
DELAY
t
PULSE
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