In message  <199703210007.SAA21738@dfw-ix9.ix.netcom.com> PICLIST@MITVMA.MIT.EDU
 writes:
> 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,

That made perfect sense - thanks.

I am counting the edges in the ISR. The edges are about 100us
apart. The next group is some 5ms later. I have a port pin
set when I enter the ISR and clear when I leave, and I have
left the ISR before the 1st edge of the second group.

Regards,


Mike Watson