Hi,

There's some basic problem in code attached [It just looks long, its a lot of cut & paste work!]. What its supposed to do is multiply a 24bit no. with an 8bit number [say CONST00 with multiplier 0007h] and store the result in a new 32-bit var (SUM3:SUM2:SUM1:SUM0). Then I have to add the next product, i.e. the product of CONST01 and 0007h to the above 32-bit sum, and so on. Also, my summing segment wouldn't work (how can I take the carries into account?)

Errors generated during building: None

Logical Error: Has to be somewhere - as the different registers don't change at all??? (Please help)

Thanks in advacne for your help/advice.

Regards,

Saurabh

PROD3  equ  10  ; products
PROD2  equ  11
PROD1  equ  12
PROD0  equ  13
TWOFOUR3 equ  14  ; multiplicand
TWOFOUR2 equ  15
TWOFOUR1 equ  16
TWOFOUR0 equ  17
mulitiplier equ  18  ; multiplier
SUM3  equ  19  ; Sum
SUM2  equ  20
SUM1  equ  21
SUM0  equ  22

;TABLE_COEFF

#define  CONST00  0x082613
#define  CONST01  0x0
#define  CONST02  0xfFF26
#define  CONST03  0x0
#define  CONST04  0x28BE61
#define  CONST05  0x400000
#define  CONST06  0x28BE61
#define  CONST07  0x0
#define  CONST08  0xFF26
#define  CONST09  0x0
#define  CONST10  0x082613
#define  multiplier 0x007

;*************************************RESET VECTOR****************************************

ORG 0000h
GOTO BEGIN

;**********************************INTERUPT VECTOR****************************************

;******************************************* MAIN PROGRAM ********************************

BEGIN:
movlw (const00 >> 16)
movf twofour2
movlw ((const00 >> 8) & 0xFF)
movf twofour1
movlw (const00 & 0xFF)
movf twofour0

goto mult24x8
goto multloop
goto suminit
goto sum

movlw (const01 >> 16)
movf twofour2
movlw ((const01 >> 8) & 0xFF)
movf twofour1
movlw (const01 & 0xFF)
movf twofour0

goto mult24x8
goto multloop
goto sum

movlw (const02 >> 16)
movf twofour2
movlw ((const02 >> 8) & 0xFF)
movf twofour1
movlw (const02 & 0xFF)
movf twofour0

goto mult24x8
goto multloop
goto sum

;........

goto $

;**************************MULTIPLICATION ROUTINE***************************************
mult24x8:
        clrf    prod0           ; Clear the product
        clrf    prod1
        clrf    prod2
        clrf    prod3
        clrf    twofour3        ; Clear the top byte of the multiplicand

multloop:
        movf    mulitiplier,W   ; Check to see if eight bit is empty
        btfsc   STATUS,Z        ; Done if zero
        return
        bcf     STATUS,C        ; clear carry
        rrf     mulitiplier,F   ; Get the next bit
        btfss   STATUS,C        ; Add if carry is set
        goto    multshift       ; shift only if 0
        movf    twofour0,W      ; Add the 32 bits of multiplicand to product
        addwf   prod0,F         ; each addwf sets the carry
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod1,F         ; Add one to next byte if carry occured
        movf    twofour1,W      ;
        addwf   prod1,F         ;
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod2,F         ; Add one to next byte if carry occured
        movf    twofour2,W      ;
        addwf   prod2,F         ;
        btfsc   STATUS,C        ; Don't increment if no carry
        incf    prod3,F         ; Add one to next byte if carry occured
        movf    twofour3,W      ;
        addwf   prod3,F         ;

multshift:
        bcf     STATUS,C        ; clear carry
        rlf     twofour0,F      ; Shift the 24 bits one bit to the left
        rlf     twofour1,F
        rlf     twofour2,F
        rlf     twofour3,F
        goto    multloop

;**************************ADDITION ROUTINE***************************************

Suminit:
clrf sum3;
clrf sum2;
clrf sum1;
clrf sum0;

Sum:
movf prod3,w
movf sum3
movf prod2,w
movf sum2
movf prod1,w
movf sum1
movf prod0,w
movf sum0