----------
> From: Andrew Warren <fastfwd@IX.NETCOM.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Tmr1 interrupt on a 16C73
> Date: Thursday, March 20, 1997 6:15 PM
>
> 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