Mark,

You've understood my problem. My code is all in bank 0 and I don't need =
to save pclath, W reg, Status etc. Thanks for the encouragement that the =
code seems to be ok. I'll have to keep trying.

David,

I will take a look at those links you suggest to see if something jumps =
out at me.........
  ----- Original Message -----=20
  From: Mark Newland=20
  To: PICLIST@MITVMA.MIT.EDU=20
  Sent: Monday, June 18, 2001 9:31 PM
  Subject: Re: [PIC]: 16F876 Interrupts


  David,
       This is not always needed.  You only have to "save all kinds of =
stuff" if it is
  needed to be saved.  I have MANY times had a simple little program =
where my code
  went something like:

  Main
       btfss     TMR_F
       goto     Main
       bcf       TMR_F
       ......
       goto     Main

  All my interupt routine does is set TMR_F.  I then waste time in the =
first two lines
  of my code waiting for the timer to overflow.  I don't care about =
saving anything
  cause I start everything over again after the interrupt.

  I will state AGAIN what his request was.  His request was not how does =
he handle the
  internals of the interupt routine.  His request was how does he get =
the interupt
  routine to execute.  Or to put it in his own words, "...the timer 1 =
overflow flag
  gets set, but never calls the interrupt vector."

  David,
       On the other side of the arguement, you are correct that he =
should at least be
  aware that certain values MAY need to be saved.  I know that when I =
first started,
  this gave me headaches also.

  Malcolm,
       Assuming that your problem is not saving certain registers but is =
indeed as you
  stated, "...the timer 1 overflow flag gets set, but never calls the =
interrupt
  vector" all I can say is that I can't find anything wrong with it.  =
Then again, I
  can't see the nose on my face sometimes either.

  David Cary wrote:

  > Dear Malcolm Peill,
  >
  > Malcolm Peill <Malcolm@PEILL.ORG.UK> on 2001-06-18 11:04:51 AM =
admitted a lack
  > of knowledge when he said:
  > >I have to admit to never having used interrupts before, so it may =
be obvious
  > >to those who have.....
  > >
  > >My code includes the following:
  > >
  > >  ORG     0x000             ; processor reset vector
  > >    goto    main              ; go to beginning of program
  > >  ORG     0x004             ; interrupt vector location
  > >
  > >  bank_low
  > >  CLRWDT
  > >  btfss PIR1,TMR1IF ;return if it wasn't a timer1 interrupt
  >
  > Yes, it's obvious. Interrupt routines need to save all kinds of =
stuff at the
  > beginning of the interrupt routine, then restore them at the end of =
the routine.
  > It's a little tricky, so everyone starts with the code in the
  >   _PIC16F87X data sheet_ by Microchip Technology Inc.
  >   http://www.microchip.com/0/lit/pline/picmicro/
  >   p. 132: Example 12-1: Saving Status, W, and PCLatH Registers
  > .
  > Also be sure to use
  >   http://piclist.org/techref/microchip/isrregs.htm
  > for a few improvements.
  >
  > --
  > David Cary
  >
  > --
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  > ways.  See http://www.piclist.com/#archives for details.

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