By the way, 1 MHz is right in the middle of AM broadcast frequency range. 20 kHz is at the edge of hearing frequency range and slightly outside of the FCC bandwidth limit. If you use 20 kHz PWM to modulate the 1 MHz, you get yourself a "digital radio of a different kind". Anyone want to try that for fun? A slightly better setup is: MCLK = DCOCLK = 12 MHz, SMCLK = DCOCLK/8 = 1.5 MHz, PWM-frequency = SMCLK/64 = 23.4 kHz Being able to Modulate the pulse-width in 512 MCLKs in an ISR is possible but not easy.
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