PIC17C44 Datasheet, PDF (50/241 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

PIC17C4X
Example 8-3 shows the sequence to do a 16 x 16
unsigned multiply. Equation 8-1 shows the algorithm
that is used. The 32-bit result is stored in 4 registers
RES3:RES0.
EQUATION 8-1:
16 x 16 UNSIGNED
MULTIPLICATION
ALGORITHM
RES3:RES0 = ARG1H:ARG1L * ARG2H:ARG2L
= (ARG1H * ARG2H * 2¹⁶) +
(ARG1H * ARG2L * 2⁸) +
(ARG1L * ARG2H * 2⁸) +
(ARG1L * ARG2L)
EXAMPLE 8-3: 16 x 16 MULTIPLY ROUTINE
MOVFP
MULWF
MOVPF
MOVPF
;
MOVFP
MULWF
MOVPF
MOVPF
;
MOVFP
MULWF
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
ADDWFC
;
MOVFP
MULWF
ARG1L, WREG
ARG2L
; ARG1L * ARG2L ->
; PRODH:PRODL
PRODH, RES1 ;
PRODL, RES0 ;
ARG1H, WREG
ARG2H
; ARG1H * ARG2H ->
; PRODH:PRODL
PRODH, RES3 ;
PRODL, RES2 ;
ARG1L, WREG
ARG2H
; ARG1L * ARG2H ->
; PRODH:PRODL
PRODL, WREG ;
RES1, F
; Add cross
PRODH, WREG ; products
RES2, F
;
WREG, F
;
RES3, F
;
ARG1H, WREG ;
ARG2L
; ARG1H * ARG2L ->
; PRODH:PRODL
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
ADDWFC
PRODL, WREG ;
RES1, F
; Add cross
PRODH, WREG ; products
RES2, F
;
WREG, F
;
RES3, F
;
DS30412C-page 50
© 1996 Microchip Technology Inc.