>Dear Piclist,
>Can anyone give me some pointers to using the RTCC interrupt on the
>16C84?
>This is how I've got it set up so far.
>
>
>
>
>start       bcf GLOBAL_INTERRUPT    ; disable interrupts
>
>; for a 2.4576MHz crystal, 2457600/256=9600
>; load rtcc with 96 giving 100 interrupts/sec

The crystal frequency is divided by four to generate the clock for TMR0, at
that frequency I would load TMR0 with 32 to get 100 interrupts/second.
2.4576/4=614.4
614.4/256=2.4
2.4K/100=24
256-24=232=E8H

>service movwf   save_w
>        movf    status,w
>        movwf   save_s


Use SWAPF intsruction. It won't affect the ZERO flag as does MOVF

ISR     movwf   W_BACKUP        ;
        swapf   STATUS,W
        movwf   STATUS_BACKUP   ;


>        bcf GLOBAL_INTERRUPT

When an interrupt occurs, GIE is cleared. You don't need to clear it. But
when you do, clear it in the following loop:

Lable   bcf     INTCON,GIE
        btfsc   INTCON,GIE
        goto    lable

0therwise, executing an interrupt and RETFIE could re-inable the interrupt
you've just tried to clear.

>---
>interrupt routine . . . .
>---

>        bsf GLOBAL_INTERRUPT

Don't do that. RETFIE will enable GIE on exit. Enabling it early can cause
recursive interrupts, and crash your stack.

>        movf    save_s,w
>        movwf   status
>        movf    save_w,w
>        retfie

        swapf   STATUS_BACKUP,W ;Restore working reg's now that ISR's done
        movwf   STATUS          ;
        swapf   W_BACKUP
        swapf   W_BACKUP,W
        retfie                  ;End of ISR


Disable RBIE and INTE if not in use, otherwise input on RB0, RB4-7 can
result in interrupts.
Good luck.