Hi.

The "Global Interrupt Enable flag" (GIE) is handled
automaticly (cleared when the interrupt code is called
and set by the RETFIE instruction). You should only
clear this bit if you want to globaly disable interrupts
*outside* of your ISR.

On the other side, you have to clear the specific "XX Interrupt
Flag" (RBIF in your case) that caused the interrupt to happen.
If not, your ISR will be called recursively as soon as he RETFIE
instruction is executed.

Now, regarding your code...

What *did* you expect ?
How *did* it work ?

One thing, this code :

        BTFSC PORTB, 7
        GOTO    BIT_7

will goto "BIT_7" if "PORTB, 7" is set ("1"), no matter
if it has changed since last time. Is that what you want ?
If you realy want to check for changes, you have to
save the last state of each bit and compare with that.

And, if two bits changes at the same time, you will probably
miss one of them.

Jan-Erik.

-----Original Message-----
From: WH Tan [mailto:tanwh@NOTES.SRC.GLOBAL.SHARP.CO.JP]
Sent: den 17 oktober 2003 06:28
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: RB change ISR


I am confuse with the following code, because it didn't work as expected.
Perhaps I am missing something. Can somebody on the list please correct my
mistake.

Thanks in advance.

WH Tan


PAGE0_START
        ORG     0x0000  ; RESET vector location
        GOTO    START

        ORG     0x0004
        MOVWF   W_TEMP
        SWAPF   STATUS, W
        MOVWF   STATUS_TEMP

        BCF     INTCON, GIE     ;Is this code is a must, or
                                ;PIC will do it for me?

        BTFSC   INTCON, RBIF    ; Check is RB change ISR?
        GOTO    ISR_RBIF                ; Yes
        GOTO    END_ISR         ; No

ISR_RBIF
        BTFSC PORTB, 7
        GOTO    BIT_7
        BTFSC PORTB, 6
        GOTO    BIT_6
        BTFSC PORTB, 5
        GOTO    BIT_5
        BTFSC PORTB, 4
        GOTO    BIT_4
        GOTO END_ISR

END_ISR
        SWAPF   STATUS_TEMP, W
        MOVWF   STATUS
        SWAPF   W_TEMP, F
        SWAPF   W_TEMP, W

        BCF     INTCON, RBIF
        BSF     INTCON, GIE             ; Again, is this code necessary?
        RETFIE

BIT_7
        ; Send send some character to LCD
        ; to indicate a change on RB7
        ....
        GOTO END_ISR

BIT_6 ~ BIT_4
        ; Do exactly same as BIT_7

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