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'No-assemble code'
1995\03\21@185217 by James L. Johnson

Hi again,

 Here's a real live example of Microchip code that won't assemble in
the Parallax PASM and I don't know why.  The error I get is in the
first line of the "test program".  The error says:

 "data was already entered at 000h"   and the line that generated it is:

 "main  movlw   0F3h"

 So ... what data was already entered?  There is no mention of a location
000h in the first place.  Perhaps this is one of those instances where
the assembler is totally confused by something else, but prints that as
the error.  You know how these software things are.

 Any ideas?


 Jim Johnson

;        include "mpreg.h"

       include 'dbl_add.asm'   ; JJ - attempt at including a file
       include 'dbl_jj.asm'    ; JJ - another include file

;       org     0
LupCnt  equ     10             ; Number of iterations
SqrtLo  equ     10             ;ACCaLO
SqrtHi  equ     11             ;ACCaHI
NumLo   equ     1Dh
NumHi   equ     1Eh
count   equ     1Fh
       movlw   LupCnt
       movwf   count
       movf    NumHi,W
       movwf   SqrtHi
       movf    NumLo,W         ; set initial guess root = NUM/2
       movwf   SqrtLo
       bcf     STATUS,CARRY
       rrf     SqrtHi
       rrf     SqrtLo
       retlw   0
div2    bcf     STATUS,CARRY
       rrf     13,W        ;ACCbHI
       movwf   SqrtHi
       rrf     12,W        ;ACCbLO
       movwf   SqrtLo
       retlw   0
Sqrt    call    init
sloop   movf    NumLo,W
       movwf   12          ;ACCbLO
       movf    NumHi,W
       movwf   13           ;ACCbHI
       call    D_divS          ; double precision division
       call    D_add           ; double precision addition
;                               ; the above 2 routines are listed
;                               ; as seperate routines
       call    div2
       decfsz  count
       goto    sloop
       goto    over            ; all iterations done
;                               ; branch back to desired location
;               Test Program
main  movlw   0F3h
       movwf   NumHi
       movlw   0F6h       ; Set input test number = 62454
       movwf   NumLo     ;  = F3F6h
       goto    Sqrt      ; cannot use CALL : Math routines
;                         ; use up all the stack.
over    nop               ; all iterations done
self  goto    self      ; result = 00F9h = 249
;                         ; exact sqrt(62454) = 249.9
       org     0
       goto    main

1995\03\22@034410 by Chuck McManis

Jim, your specific problem is this:

At the beginning of your code it starts out:

>> init
>>         movlw   LupCnt
>>         movwf   count
>> ...

Now you've commented out the org 0 so that was ignored, however
in the absence of any directive the assembler starts loading code
at location 0. (makes sense yes?)

Now later in your program you have:

>>        org     0
>>        goto    main
>>        END

Which re-sets the program counter to zero and trys to assemble the
'goto main' into that address. Which overwrites the 'movlw LupCnt'
that you had in init above.

The correct fix for this specific problem is that you should move
the 'goto main' to be the first statement in your program and then
it will assemble at location 0 and all will be well.

I both agree and disagree with what has been said about Parallax's
assembler. On the one hand, if you've got working MPASM code it can
be a real pain to get it to assemble correctly with the Parallax
assembler. On the other hand, if you learn the Parallax assemblers
quirks early on (and MPASM has its own) then writing new code from
scratch can be fairly easy in both.

The lack of a macro facility and conditional assembly in the Parallax
assembler hurt it, however if you are using Linux then you could always
run cpp over the code before feeding it to pasm.

--Chuck McManis                      All opinions in this message/article are
Sun Microsystems Inc.                those of the author, who may or may not
Internet: .....cmcmanisKILLspamspam@spam@Eng.sun.COM       be who you think it is.
Crypto-puzzle: *0U0JPFPrWRN9PkWRKeP5WRmIR9wP5QAWuIQP9Pu9tnIZ7AD1SIS

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