On Wed, Jun 22, 2011 at 6:47 PM, Brent Brown wrot= e: > > I know that no text can ever be aligned properly, but here's a cut/past= e > > from the data sheet. > > Parameter Symbol Min. Typ. Max. Unit > > PWM frequency fPWM 200 300 400 Hz > > That is curious. I still can't think of a good reason why there should be= a > maximum > spec. > Me neither. And it may just be sloppy specsmanship. "Ah, just tell 'em a couple hundred hertz. No one needs to go faster than that, anyway." But that gives me the choice of assuming I know more than they do, and risking having some problem occur later on. Not this time. As to conjectures about the dimming PWM, there are two factors I see that have to be kept in mind. One is that this product may be used at night, and the user may want to make the screen very dim. So, while it seems to make sense that I don't really need 7 or 8 bits of resolution across the full brightness range, I may well need to run at 1% duty at the dim end, somehow= .. Factor number two is that 1% at 200 Hz is 50us, and if I introduce a 10us disturbance into that pulse, it's wrong by 20%, and that will be visible as a flicker. I like the idea of the timers being used for the high and low portion of th= e cycle. I even believe that it may be less important to keep the frequency exact, as long as the "on" duty time doesn't jump around. That's relevant because I'm concerned about reloading the timers to account for variable software overhead. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .