RM0312 datasheet(137/275 Pages) STMICROELECTRONICS

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RM0312

16-bit general purpose timer (TIM2/TIM3)

170

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 clock/trigger 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 up-counting: CNT<CCRi

≤ ARR (in particular, 0<CCRi),

In down-counting: CNT>CCRi.

Figure 59. Example of one pulse mode

For example you may want to generate a positive pulse on OC1 with a length of tPULSE and

after a delay of tDELAY as soon as a positive edge is detected on the TI2 input pin.

Let’s use IC2 as trigger 1:

•

Map IC2 on TI2 by writing CC2S=0b01 in the TIMx_CCMR2 register.

•

IC2 must detect a rising edge, write CC2P=’0’ in the TIMx_CCER1 register.

•

Configure IC2 as trigger for the clock/trigger controller (TRGI) by writing TS=0b110 in

the TIMx_SMCR register.

•

IC2 is used to start the counter by writing SMS to 0b110 in the TIMx_SMCR register

(trigger mode).

TI2

TIMx_ARR

TIMx_CCR1

OC1

tDELAY

tPULSE

OC1REF

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