Measuring audio phase shift through a circuit with a PIC

[HankMcSpank]

You may have already corrected this, but on the original code the analog inputs for the comparators are not enabled (ANSEL.6 and ANSEL.7). Minor thing, but shouldn't hurt to follow the datasheet.

I had thought the ANSEL turned on/off the AtoD for a given pin - certainly my comparators have been working with the corresponding ANSEL deselected? I had a similar discussion with Melanie & she considered them digital....

http://www.picbasic.co.uk/forum/show...1127#post81127 extract here....

Whether you consider a Comparator OUTPUT as analog I suppose is up to you. I consider Comparators INPUT as ANALOG but technically their OUTPUT is DIGITAL since it can only be a High or a Low. RC4 is the OUTPUT for Comparator 2. If you are using Comparator 2, you DON'T want to set that pin to ANALOG (because ANALOG refers really only to INPUTS), but you want DIGITAL OUTPUT.

Since then I've assumed digital & therefore deselected the analog!!

I do agree with other suggestions, since the inputs are already digital there is not need to use the comparators. But to use the IOC (interrupt-on-change) you would most likely need to go for PORTA or PORTB (which have individual IOC bits for each input).

I already use IOC (for switching) in the program that this melarkey is destined for - in my blissfully naive planet of "don't understand", for now, I'd prefer to keep the two interrupt variants apart! (for fear of IOC contention)

General suggestion for interrupt use: keep everything short; do only the absolute minimum inside the interrupt routine.

I would agree with that, but what I've found is that unless I do stuff inside the routine, then the counts go to pot! (that's not to say I shouldn't strive to do such stuff outside the routine, but as of yet, I'm having the most success keeping it 'controlled' where I know where/when it's going to be used!

Even though the use of the HW USART (HSEROUT) is a plus, you should still try to do this outside the interrupt routine. Do the timer stuff inside the interrupt (i.e. clear and set timer, etc). Make a flag that tells you the interrupt "fired"; and in the main loop manipulate the data to be sent out (and send it out). I think the CCP module maybe a much better candidate for what you are doing.

I'd love to get that HSEROUT outside....but I think therein lies the possible original problem?

It would be nice to slowly build the picture up to see when the trouble occurs, but to do that I need some clever person to tell me how I can 'trigger' the code that 'works' above into action while the main program is running?