A/D IO pins changing function while running?

[Art]

I found this interesting so looked a bit more...
I've done a couple of projects with analogue in that worked great

I think your program is resetting bits in ADCON1 register and resetting ports back digital
depending on the value read from the port that starts out analogue.

For an 8 bit result, setting ADCON1:7 to zero sets the 10 bit result left justified so you
only see the high 8 bits in the word which are most significant because you access the
high byte of a word with the 10 bit result shifted into place.
How much of this is handled by PBP I don't remember, but that's what's happening.
Otherwise the 10 bit result is right justified, and you see a 16 bit word who's leading
6 bits are always zero, and that's the 10 bit result.

I'll bet that you're making PBP access a 16 bit word comprised of the ADCON1 register,
and the lower end result register, and that's somehow enough to wreck the contents
of ADCON1, and leave your program running with a digital port.

I was thinking asm when doing this,
it would be nice if someone else has any thoughts on what PBP is doing.
I suspect the DEFINE would set the ADCON1 bit 7 without touching the other bits,
and setting it again directly might only override it.

[peterdeco1]

I had some issues in the past similar to this. Try putting your main001: label under your DEFINEs so it essentially reboots each time it goes there.

[TerdRatchett]

Thanks Art, I corrected that error but the problem persists. What I have found is that while in a tight loop reading any A/D input the input impedance becomes much lower and causes A/D readings that are way out of whack. For example; I have a 10k input resistor and there is .212 volts on the input and .108 on the processor side while continuously reading. If I comment out the line that reads the A/D I get .212 volts on both sides of the resistor.

[TerdRatchett]

In addition if I comment out the line that turns on PWM I get no voltage drop across the input resistor and the A/D reads the voltage correctly. It almost appears as if the PWM is affecting the A/D.

[peterdeco1]

If you connect your PWM output to a scope or even an LED, does it behave correctly?

[TerdRatchett]

Thanks to everyone for their help! I found the actual problem yesterday. As it turns out there was a transient coming in on an A/D pin other than the one I was using to measure the high voltage. I removed that input and the product regulates precisely. Lesson learned: transient voltages on any A/D input can effect the operation of other inputs of the A/D input multiplexer.

TR

[Art]

It's hair pulling stuff when your programming problem was really an electronics problem,
or vice versa.