Hi Mike,

> I am having difficulty getting MPSim in MPLab to detect that tmr0 on
> a C84 has overflowed. I'm not using interrupt, just polling the bit,
> but it never detects the bit change, even though it works in the
> part itself.

Been playing with exactly the same things the whole weekend.

I have not used it with the prescaler yet but you must keep an eye
on the interaction between the cwdt command and the prescaler, there
may be some incorect mutual effects there.

You have used the wrong flag.

> ; now set up rtcc to count out every 5 ms
>         bsf     sts, rp0
>         movlw   b'10000100'     ; assign ps to rtcc
>         movwf   OptReg          ; ps = 32
>         bcf     sts, rp0
>         movlw   .94
>         movwf   RTCC
>
>
> ; Main loop is here
>
> mainloop
>
>         btfss   intcon, rtif
>         goto    mainloop                ;loop until rollover occurs
>
>         bsf     port_A, 0
>         call    ServiceRTCC
>         bcf     port_A, 0
>         goto    mainloop
>
>
> ServiceRTCC
>         movlw   Tmr5ms                  ; re-initialise the timer
>         movwf   rtcc
>         bcf     intcon, rtif
>
>         ; do other stuff
>
>         return

The rtif is used for the port B0 interrupt (selectable edge polarity in
OPTION register) and th T0IF is used for the timer 0 overflow flag.

BitLoop
        btfss   INTCON, T0IF    ; spin on bit counter
        goto    BitLoop

The above works fine.

Cheers
--
Kalle Pihlajasaari     kalle@data.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751