Is there a software way to count pulses of pwm pins?

[danko]

Hi all, I want to run very precise PWM.
Can I start and stop PWM, after a number of pulses. Is there a software way to count pulses of pwm pins?
Thanks !

[temtronic]

Yes
Tie the PWM output pin to an input pin that can be used as an interrupt source.In the ISR just increment a variable.
Now as to how good this will work...
...technically it does work, however due to ISR overhead and othr issues the 'precision' may not be acceptable for your application which we know nothing about or the PIC you've chosen.

hth
jay

[danko]

I need a 64 KHz PWM , after each 32 pulse must stop for a period of 32 pulses. I have not chosen a specific PIC, a 12F1840 seems good. Is there a "software" way, for example: to check the timer register, or something But there is no problem to do it with external interrupt. Thanks.

[Mike Walne]

Depends on which PIC you choose.

Assuming you use Timer2 for the timebase, you can use the post scaler to generate an interrupt after several PWM cycles.

With say a 18F1320 you could interrupt after 16 cycles. Significantly reduces the work load.

Mike

[Ttelmah]

Alternatively, feed the PWM output back in, as the clock input to any other timer. Clear the timer, start the PWM, and then set the pulse width to '0', when the timer reaches 31 (remember the pulse width updates on the _next_ PWM pulse the 32nd pulse will have already started when you count 31).
If you want, you could use a timer than can feed a CCP, and program this to interrupt when the count gets to 31.

Best Wishes

[Mike Walne]

I was thinking along these lines.

Let Timer2 post scaler interrupt every 16 Timer2 cycles, then loop as:-

1) Wait for two interrupts, turn PWM on.
2) Wait for two more interrupts, turn PWM off.
3) Loop back to 1.

There will be a delay from interrupt to turning PWM on/off.
If both delays are identical you should get exactly what you want.

Mike

[Ttelmah]

Yes. That should work.

Best Wishes