Hello,

I also thought about that.

But context is completly saved when jumping to the interrupt routine. And
this was working with the same firmware on the older production boards.
And I made also a try and, direct before reading the port, I set the bank
properly, but without impact on my issue.

So I do not think, it is caused by software. I think, it is something wrong
inside the PIC, but I do not know what ...

Best Jens



> Only I can think of (if that is really a software issue) is 
> that you have interrupt routine that is not saving the 
> context properly - so that you select the bank for PORTB, but 
> then an interrupt occurs, so the bank changes to TRISB and 
> you read that one instead of the port...
> 
> Tamas
> 
> 
> On Sun, Nov 9, 2008 at 3:04 PM, jmg <piclist@technetz.de> wrote:
> 
> > Hello,
> >
> > I have a small problem with a big impact on my application.
> >
> > I am using a 16F877A, running in a 5V environment with 10 MHz.
> > I am using a timer interrupt (with 25ms) to read PORTB, 
> Bit5. This pin 
> > is defined as input. There is no write at all to this pin 
> by software.
> > The internal pull-up is disabled. I am using an external 
> pull-up to 5V.
> > This
> > pin is connected to an external electronic (PS_ON_m Signal from a 
> > computer motherboard).
> >
> > When the incoming signal is high, I am always reading a high (1) on 
> > this pin by software. I have never seen, that a low was reed, when 
> > high was attached to this pin.
> > But when the signal is low, it happens, that from time to 
> time, this 
> > pin is read as 1 instead of 0. I supervised the line with 
> an osci, and 
> > I never saw a glitch or spike or whatever. To be shure, I connected 
> > the pin direct to GND. But again, from time to time, I read a wrong 
> > values. This may happen after 30 seconds fro start or even 
> after 20 minutes.
> >
> > Well, we first build this application 18 month ago, and we 
> never saw 
> > this happen(with exactly the same firmware and revision 
> number of the 
> > PIC. Now, we had to build new boards, and now we have this issues.
> >
> > I first though, we could could have a problem with the pic 
> itself, so 
> > we checked for datecodes. The very first (we no issue) had 
> been from 
> > 2006, the failing ones had been from 2007. So we decided to replace 
> > the pic on one board. Now, with datecode from 2008, we 
> still see this 
> > issue. And we see it on all produced boards, meaing, we should not 
> > have shorts or bad soldering (very unlikly to have the same 
> fault on 5 boards).
> >
> > Any ideas, what could happen here?
> >
> > Best Regards
> >
> > Jens
> >
> > --
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> > membership options at 
> http://mailman.mit.edu/mailman/listinfo/piclist
> >
> 
> 
> 
> -- 
> Rudonix DoubleSaver
> http://www.rudonix.com
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
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