Hello,
Hope you are going well. The pin functions for each pin are mentioned in the Chapter 11 of the User Manual. These functions are defined and cannot be changed, you can only select one of those functions to configure the pin.
The PIO0_20 has many options, one of them can be configured in SCT for input only. If you want an output of the module for PWM, you must use a pin that has it, for example the PIO3_14 or the PIO3_28. You can find this information in the Chapter 6 of the Datasheet.
Let me know if you have further questions.
Best Regards,
Ricardo
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