I would not use a PWM mode to try to make a three phase waveform. Instead you should use a microcontroller with a PCA in it. Three PCA channels would each be used in HIGH SPEED MODE. (If you are unfamiliar with the PCA and the high speed mode there is a link in the LINKS section to the left that lets you read the old Intel PCA Cookbook document). Next you need to setup the match register for each of the three channels to the time sequence when you want the outputs to change state. Then you enable the outputs of the three channels to start and they will toggle at the appropriate time to start the three phase waveform sequence. Also enable the interrupt for each of the three channels and when any of these occur then update the corresponding match register to control when the next edge change should occur on that channel. Using this technique it should be possible to generate almost any waveform you desire. The two limitations are.....

1) The maximum width of any channel in the low or high state at the output is limited to the 2**16 counts of the free running counter value.

2) The minimum width of any pulse width (High or Low at output) is limited to the time it takes to respond to the interrupts and then process those interrupts in software.

Using the PCA is nice because in the PCA the output toggles in HIGH SPEED MODE toggle before the interrupt occurs. This makes it possible to get the next output toggle point setup in software before the next edge time will occur.

It will be easy to make waveforms that look line any of the following....



Michael Karas