7.4.12.2 PWM1-4

Pins 31, 32, 41, and 42 can be used as GPIs or PWM outputs.

If configured as PWM outputs, then limitations apply:

• PWM1 has a fixed frequency of 10 kHz
• PWM2 has a fixed frequency of 1 kHz
• PWM3 and PWM4 frequencies can be 0.93 Hz to 7.8125 MHz.

The frequency for PWM3 and PWM4 is derived by dividing down a 15.625MHz clock. To determine the actual frequency to which these PWMs can be set, must divide 15.625MHz by any integer between 2 and (2²⁴-1). The duty cycle resolution will be dependent on the set frequency for PWM3 and PWM4.

The PWM3 or PWM4 duty cycle resolution is dependent on the frequency set for the given PWM. Once the frequency is known the duty cycle resolution can be calculated as Equation 2

To determine the closest frequency to 1MHz that PWM3 can be set to calculate as the following:

1. Divide 15.625MHz by 1MHz to obtain 15.625.
2. Round off 15.625 to obtain an integer of 16.
3. Divide 15.625MHz by 16 to obtain actual closest frequency of 976.563kHz.
4. Use Equation 2 to determine duty cycle resolution to obtain 6.25% duty cycle resolution.

All frequencies below 238Hz will have a duty cycle resolution of 0.0015%.