At 01:05 PM 1/3/01 -0500, David VanHorn wrote:
>I'm confused.
>
>I've set timer0 to run, and I'm polling as follows for the T0IF bit.
>
>Comm_Bit_Loop:
>        btfss   INTCON,T0IF             ;Check for timer hitting zero
>        goto    Comm_Bit_Loop           ;If not, then keep looping
>
>It appears that the int flag is never set.
>Ints are disabled, but I thought I read that the int flag would still be
>set on rollover.

I *know* for a fact that T0IF is set upon timer 0 rollover regardless of
the state of T0IE.  In fact, I have several dozen projects using that very
technique.  It lets me make my background task a polled routine and thus
reserve the ISR for time critical routines.

I would check the option register bit 5 (T0CS) - TMR0 can be configured for
external clock input.  It sure sounds like TMR0 isn't clocking.

I also do a lot of work with 12 bit core parts - no T0IF.  But its not much
of a problem - I make my "flag test" routine look for TMR0 bit 7 to go low,
then look for it to go high.  i.e. . ...

WaitBGflagLO
     btfss  TMR0,7
       goto WaitBGflagLO
WaitBGflagHI
     btfsc  TMR0,7
       goto WaitBGflagHI
;BG task starts here

You have to do both tests (bit 7 lo, then high) to avoid having to reset TMR0.

dwayne



Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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