I have seen something like this before, my timer worked fine then suddenly =
it would go berserk and shoot off into hyperspace, after trying everything =
we could think of I noticed a hair-line solder bridge between two outputs, =
so when one turned on it tried to drag the other one up and the PIC didn't =
like it at all, but crucially didn't totally stop working either.
It wasn't visible with the naked eye, and we only saw it when we got the =
board under a microscope, it's worth considering, we got too stuck on the =
software and didn't consider a hardware problem could possibly cause an =
apparent software problem :{

Good luck !

Jonathan Starr

R&D Technician
Electronix Limited

Tel +44 (0)1993 700510
Fax +44 (0)1993 700511


e-mail jonathans@electronix.co.uk=20

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--


>Hi Peter.
>I just did an MPLAB sim on your asm version.  It works as you would =
expect.
>I also ran it as a 16C73 on my trusty old PICmaster emulator (won't do
>877s) and it works the same as the sim. TMR0 increments by ones and >twos =
as
>advertised depending on the instruction type.  BTW, your equates need to =
>be
>moved up to 0x20 or higher.  Right now, they are in the middle of the =
SFRs.
>
>Now for the real question -- is your program really working and your
>emulator just isn't showing you or is there really something wrong?  What
>you should do is calculate your TMR0 interrupt rate and toggle an output
>pin.  Monitor the pin with a scope to see if it happens at the right =
rate.
>If it does, at least you can keep developing with some degree of =
confidence
>until we can sort out why TMR0 doesn't look like it works.  If not, might
>be time to call your emulator manufacturer and talk to him.
>
>Bill
>
>At 08:08 AM 06/10/2002 +0100, you wrote:
> http://www.piclist.com/postbot.asp?id=3Dpiclist\2002\06\07\153942a=20
>
>Thanks for the reply and yes I hadn't assigned the Prescaler in that
example,BUT this is not the real problem.
>
>I have written other code to select the prescaler for the TMR0 but is not
that the PIC isn't counting/timing at the correct rate it's more drastic...=
.
>
>*** the TMR0 register is just RANDOMLY changing ****
>I can see no sequence in the numbers at all. They appear to just change =
at
will on every instruction.
>
>When I run this in the simulator all is well and I get the TMR0 register
changing as expected.
>So why NOT on the real hardware???
>
>I have now written it in assembler and still I must be missing something
obvious...
>
>; Use PIC16F84 and set radix system to decimal
>        LIST P=3D16F877, R=3DDEC
>
code snipped...

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