Mayes uk <mike@d-m-g.demon.co.uk> wrote:

> I am having problems with the interrupt on Tmr1 on a C73.
>
> I have it configured to interrupt from a RC0, I set Tmr1H
> and Tmr1L to $FF.
>
> The first time a +ve edge comes along I get the interrupt,
> which is then followed by 3 other +ve edges, I do what I have
> to do, then on leaving the interrupt handler set Tmr1H and
> Tmr1L back to $FF and clear the Tmr1IF ready for the next time.
>
> The next +ve edge comes along and gets ignored. The one after
> that causes an interrupt and off I go, but this time I am
> one edge out of sync.
>
> Anyone got any ideas?

Mike:

Is it possible that, rather than ignoring 3 edges while you're in
your interrupt service routine, you're actually ignoring FOUR?  If
you're still in the interrupt routine when the edge you want comes
through, clearing the TMR1IF flag will keep it from being processed.

I don't know how you're ignoring those three edges, but if you're
actually counting those edges in the ISR, you should clear the TMR1IF
flag IMMEDIATELY after seeing the third ignored edge.  That way, if
the fourth edge comes through before you exit the ISR, it'll generate
an interrupt as soon as your RETFIE is executed.

Did that make sense?  If not, let me know and I'll rephrase it... I'm
pretty tired right now.

-Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering, Vista, California
=== http://www.geocities.com/SiliconValley/2499