Wan Zulhelmi Wan Ahmad Kamar wrote :

> Hi, i've been trying to simulate a timer interrupt but it doesn't
> work.  Anybody have any suggestion?  Based on the code elow tmrcounter
> should increment on every interrupt so that i can calculate time more
> than the 16 bit timer register.  The scale of the timer is 1:8.
> Thanks in advance.
> 
>        LIST            p=18f252
>        INCLUDE         <p18f252.inc>
> 
> CounterA        equ     0x00
> CounterB        equ 0x01
> CounterC        equ 0x02
> tmrcounter      equ     0x03
> W_SAVE          equ     0x05
> STATUS_SAVE equ 0x06

You don't need W_SAVE and STATUS_SAVE on the PIC18.

> 
>        ORG 0000H
>                GOTO MAIN
>                ORG 0008H
>                GOTO INT_SERV
> 
> MAIN
>        CLRF            PIR2,1   ;Register Overflow

What us ",1" ? Use the symbols in the INC file !

>        CLRF            TMR3H
>        CLRF            TMR3L
>        MOVLW           0x80
>        MOVWF           INTCON
>        MOVLW           0x02
>        MOVWF           PIE2    ;TMR3 Overflow Interrupt
>        MOVLW           B'00110000'
>        MOVWF           T3CON
>        BSF             T3CON,0

What us ",0" ? Use the symbols in the INC file !

> 
>        ;  Loop for 1 second

What are you waiting for ?

>        movlw   D'26'
>        movwf   CounterC
>        movlw   D'119'
>        movwf   CounterB
>        movlw   D'87'
>        movwf   CounterA
> loop
>        decfsz  CounterA,1
>        goto    loop
>        decfsz  CounterB,1
>        goto    loop
>        decfsz  CounterC,1
>        goto    loop
> 
>        BCF     T3CON,0
>        GOTO    FINISH
> 
> INT_SERV     ;Interrupt Routine
> 
>    MOVWF W_SAVE        ; save W
>    SWAPF STATUS, W     ; save STATUS
>    MOVWF STATUS_SAVE

No need to do that on the PIC18 !

> 
>    INCF tmrcounter, 1                 ;increment on every overflow

Do not use ",1". Use the symbols in the INC file.

> 
>    SWAPF       STATUS_SAVE, W
>    MOVWF       STATUS; restore W and STATUS
>    SWAPF       W_SAVE, F
>    SWAPF       W_SAVE, W

No need to do that.

>    CLRF                        PIR2,1   ;      CLEAR Register Overflow

Use the symbols in the INC file.

>    RETFIE

Use "RETFIE, FAST"

> 
> FINISH
>        END

Here the PIC will just run thought the rest of the prog mem
and restart from h'0000'. Is that realy what you want ?

Jan-Erik.

PS.
I changed *one single bit in one register" and your code works
just as you posted it...
Hint : check PEIE :-)
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