On Wed, 17 Feb 2010 12:28:37 +1300, "ivp" said: > > If you're not doing anything in the main line then everything is fine > > but if you need to do any kind of real work in the main line then > > you shouldn't be sloppy about your interrupt handler > > one could say you shouldn't ever be sloppy ;-)) > > I did say "largely irrelevant". Each project must be assessed on its > merits. For some projects time management is critical, for others > not so critical. If even well-managed necessary tasks are causing a > particular micro to run out of processing power then dot dot dot In something realtime like this you just need to count cycles and make sure there won't be any surprises. You can generate 4 square waves with a software DDS in a 16F using timer interrupts every 20 milliseconds. In an 18F you can do everything twice as fast, and you get interrupt priority thrown is as a bonus. Or use a DSPIC and do it in even fewer cycles :) As long as you can tolerate some jitter a DDS is the way to go. Cheers, Bob -- http://www.fastmail.fm - Email service worth paying for. Try it for free -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist