PIC17C7XX_13 Datasheet, PDF (68/306 Pages) Microchip Technology – High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
Example 9-3 shows the sequence to do a 16 x 16
unsigned multiply. Equation 9-1 shows the algorithm
that is used. The 32-bit result is stored in 4 registers,
RES3:RES0.
EQUATION 9-1:
16 x 16 UNSIGNED
MULTIPLICATION
ALGORITHM
RES3:RES0 = ARG1H:ARG1L  ARG2H:ARG2L
= (ARG1H  ARG2H  2¹⁶)
+
(ARG1H  ARG2L  2⁸)
+
(ARG1L  ARG2H  2⁸)
+
(ARG1L  ARG2L)
EXAMPLE 9-3:
16 x 16 UNSIGNED
MULTIPLY ROUTINE
MOVFP
MULWF
MOVPF
MOVPF
;
MOVFP
MULWF
MOVPF
MOVPF
;
MOVFP
MULWF
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
ADDWFC
;
MOVFP
MULWF
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
ADDWFC
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
PRODL, WREG ;
RES1, F
; Add cross
PRODH, WREG ; products
RES2, F
;
WREG, F
;
RES3, F
;
DS30289C-page 68
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