Gating PWM output

Hithesh

Genius 3290 points

Let's say I have a PWM output of 100KHz and I wanna modulate this or gate this.

How do I go about doing this?

over 14 years ago

0 old_cow_yellow over 14 years ago

Guru 58965 points

Most likely, the PWM output signal shares a pin with PxOUTy as selected by PxSELy setting. If that is the case, set PxOUTy to a state that matches your inactive state of your PWM. You can now "gate" your PWM with PxSELy.

0 old_cow_yellow over 14 years ago in reply to old_cow_yellow

Guru 58965 points

You could also use OUTMOD bits to suspend the PWM output.

0 Hithesh over 14 years ago in reply to old_cow_yellow

Genius 3290 points

Can I change the PSEL or the OUTMOD every 1ms? Will the change occur asap or after a small delay?

(The modulation frequency is 1KHz)

0 Jens-Michael Gross over 14 years ago in reply to old_cow_yellow

Guru 227245 points

old_cow_yellow said:
You could also use OUTMOD bits to suspend the PWM output.

THis is the better way (switch to reset, or set mode), as it synchronizes the deactivation (and reactivation) to the PWM cycle end.

0 Hithesh over 14 years ago in reply to Jens-Michael Gross

Genius 3290 points

So both PSEL and OUTMOD can be changed within 1ms?

0 old_cow_yellow over 14 years ago in reply to Hithesh

Guru 58965 points

Yes.

If you use PSEL, its action is like a true "AND Gate". That is, the PWM is turned on/off at the same instance PSEL is changed.

If you use OUTMOD, its action is synchronized with the PWM pulses and thus delayed.

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Gating PWM output