forTe wrote:

So that I make sure, I should use PWM for this task correct?

the pwm would be the easiest way to generate a fixed or oscillating
frequency square wave from the uC.

But

If you want to show people what frequency deviation is, here's an
idea. I don't know what chip you are using to skew the clock (the chip
under test), but if it can handle clock I/O frequencies of around 3 MHz,
you could use an audio coax s/pdif signal as the clock source and run
that through your chip(s) and run the resulting signal back to a s/pdif
to analog converter (like in most modern stereo amps). Then you could
HEAR the frequcncy deviations in noise.

the a-d
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