Jim

You need to explicity set the value of the high byte of the program counter
using PCLATH. This must be done before the ADDWF PCL instruction. See
section on PCL and PCLATH in the datsheet.

For midrange PIC (16F877), I write:
    movlw    0
    call        getvalue
    ...
getvalue:
        <---------------------------------              Set value of PCLATH here ie:    Movlw
xx(value depends on location on code page)
    addwf    PCL, F                                                     Movwf PCLATH
    retlw      B'10100000'
    ...etc.

Ian Rozowsky
R&D Director
Centurion Systems (Pty) Ltd.
Box 506 Cramerview 2060 South Africa
roz**@centsys.co.za
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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jim Tellier
Sent: 25 July, 2003 09:58
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: computed goto question...


OK, this seems embarassingly simple, but...
For midrange PIC (16F877), I write:
    movlw    0
    call        getvalue
    ...
getvalue:
    addwf    PCL, F
    retlw      B'10100000'
    ...etc.

All code is within page 0 (< 2048 bytes).  Single step thru, upon exec the
'addwf' the simulator says W=0, but the retlw isn't executed... control
jumps off into middle of some other code.
I'd swear I've used this construction before, but this isn't flyin'!  Any
ideas?   Thanks!
Jim

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