PWM. - Here is Introduction 8 Channel Proportionally Spaced PWM For AVR Microcontrollers without Circuit Schematic. The assembly code given here was written to see what it would take to make an AT90S1200 generate 8 channels of proper PWM. In this case, by proper, I mean with the maximum high frequency content consistent with the needed duty cycle and give clock. Take a look at the scope shots below and notice that when the data value is =$02, there pulse frequency is twice that which occurs when the data value is =$01. The significance of this is that the percent of ripple voltage out of the low pass filter stays much more constant as the data values change than they would with a conventional PWM that merely varies the width of a single pulse (see the auto zero code for the RF Field Strength Probe for an example of code that does this). Take a look at the pictures below to see the effect.