PWM

[SveinR]

Hi,

I have been using one PWM in some projects, but I'd like to add one more with a different frequency.

As I understand from the datasheets, many of the MCU have more than one PWM.

I haven't succeeded in using more than one PWM.

Is it possible to use more than one PWM independently


Thanks

[Ttelmah]

You have to be very careful when searching. For example, chips with the full bridge PWM module, will have four PWM pins, but only one actual 'channel'.

For 90% of the chips, with two PWM's, the PWM's both use the same oscillator, so can give you two signals at the same frequency, but with different pulse widths. Similarly the power control module supports three different channels, but only one oscillator source.

If you must have separate frequencies, you need to be looking at one of the later chips with multiple PWM clock sources. For example the PIC18FxJ50, has two ECCP modules, which can be set to use Timer2 and Timer4 respectively. This then allows different frequencies on the two PWM's.

Why do you need different frequencies though?. For PWM, normally it is the mark/space ratio that matters, and the frequency is not that critical, which is why the modules share this resource.

Best Wishes