PWM on the FEZ Cerberus Mainboard

[ChrisO]

@Aron

As you can see PWM_0 and PWM_2 [b]share the same timer /b and therefore cannot be different frequencies, only different duty cycles. As you can also see, PWM_4 and PWM_5 are also on the same timer (TIM3) and therefore cannot have different frequencies, only different duty cycles.

Aron, EXCELLENT explanation thank you! It clarify s what I said above.

This is how it should have been explained and yes it needs to be in the Developers Guide, this is essential information for many when planning projects.

For many, PWM is useless unless the frequency can be changed!

Realistically, any situation where a Timer is shared, it should not be classed as PWM, instead maybe as Shared PWM because this is not true PWM as there is no ‘Modulation’ component to fixed frequency DC Pulses as Duty Cycle is proportional to Frequency.

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique that controls the width of the pulse, formally the pulse duration, based on modulator signal information.

Ref: Pulse-width modulation - Wikipedia

This means that the Cerberus Specs should read:

PWM = 4 (Pin 8 on X3, Pin 9 on X3, Pin 7 on X4, Pin 9 on X4)
Shared PWM = 2 ((Pin 7 on X3 shared with Pin 8 on X3) (Pin 8 on X4 shared with Pin 9 on X4))

Thanks again Aron.

All the Best

Chris