PIC18CXX2_13 Datasheet, PDF (62/304 Pages) Microchip Technology – High Performance Microcontrollers with 10-bit A/D

PIC18CXX2
EXAMPLE 6-3:
16 x 16 UNSIGNED
MULTIPLY ROUTINE
MOVF
MULWF
MOVFF
MOVFF
;
MOVF
MULWF
MOVFF
MOVFF
;
MOVF
MULWF
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
;
MOVF
MULWF
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
ARG1L, W
ARG2L
; ARG1L * ARG2L ->
; PRODH:PRODL
PRODH, RES1 ;
PRODL, RES0 ;
ARG1H, W
ARG2H
; ARG1H * ARG2H ->
; PRODH:PRODL
PRODH, RES3 ;
PRODL, RES2 ;
ARG1L, W
ARG2H
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG, F
RES3, F
; ARG1L * ARG2H ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
ARG1H, W
ARG2L
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG, F
RES3, F
;
; ARG1H * ARG2L ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
Example 6-4 shows the sequence to do a 16 x 16
signed multiply. Equation 6-2 shows the algorithm
used. The 32-bit result is stored in four registers,
RES3:RES0. To account for the sign bits of the argu-
ments, each argument pairs’ Most Significant bit (MSb)
is tested and the appropriate subtractions are done.
EQUATION 6-2:
16 x 16 SIGNED
MULTIPLICATION
ALGORITHM
RES3:RES0
= ARG1H:ARG1L  ARG2H:ARG2L
= (ARG1H  ARG2H  2¹⁶)+
(ARG1H  ARG2L  2⁸)+
(ARG1L  ARG2H  2⁸)+
(ARG1L  ARG2L)+
(-1  ARG2H<7>  ARG1H:ARG1L  2¹⁶)+
(-1  ARG1H<7>  ARG2H:ARG2L  2¹⁶)
EXAMPLE 6-4:
16 x 16 SIGNED
MULTIPLY ROUTINE
MOVF
MULWF
MOVFF
MOVFF
;
MOVF
MULWF
MOVFF
MOVFF
;
MOVF
MULWF
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
;
MOVF
MULWF
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
;
BTFSS
BRA
MOVF
SUBWF
MOVF
SUBWFB
;
SIGN_ARG1
BTFSS
BRA
MOVF
SUBWF
MOVF
SUBWFB
;
CONT_CODE
:
ARG1L, W
ARG2L
; ARG1L * ARG2L ->
; PRODH:PRODL
PRODH, RES1 ;
PRODL, RES0 ;
ARG1H, W
ARG2H
; ARG1H * ARG2H ->
; PRODH:PRODL
PRODH, RES3 ;
PRODL, RES2 ;
ARG1L, W
ARG2H
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG, F
RES3, F
; ARG1L * ARG2H ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
ARG1H, W
ARG2L
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG, F
RES3, F
;
; ARG1H * ARG2L ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
ARG2H, 7
SIGN_ARG1
ARG1L, W
RES2
ARG1H, W
RES3
; ARG2H:ARG2L neg?
; no, check ARG1
;
;
;
ARG1H, 7
CONT_CODE
ARG2L, W
RES2
ARG2H, W
RES3
; ARG1H:ARG1L neg?
; no, done
;
;
;
DS39026D-page 62
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