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Within these pages, you can find many useful pieces of code mostly in assembly for the Microchip PIC micro controller family. A lot of people have spend many hours trying to put the bits and bytes together. If the code is NOT written by a member of the PCB Heaven community, then a link will be added above the code with the original website that this code was found.
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View code
16bit X 16bit Signed
Author: Malin
This code was originally located @ http://www.piclist.com
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;signed multiply of a2:a1 with b2:b1 leaving result in res4:res3:res2:res1
; These 8 variables need to be defined, as does neg_flag
;
; Program length 64 lines
; time 134 to 248 cycles
; This program looks at the lsb of a1 to decide whether to add b1 to res2
;
; and b2 to res3, with appropriate carrys
; It then looks at the lsb of a2 to decide whether to add b1 to res3 and
; b2 to res4, again with appropriate carrys.
; The rotates then only have to be done 8 times
;
; This is uses slightly more program but takes a little less time than
; a routine that performs one 16 bit addition per rotate and 16 rotates
;
; Multiple byte addition routine from Microchip AN617
; Result registers used as loop counter from Bob Fehrenbach & Scott Dattalo
;
clrf res4
clrf res3
clrf res2
movlw 0x80
movwf res1
clrf neg_flag
btfss a2,7
goto a_pos
comf a2,f
comf a1,f
incf a1,f
btfsc status, zero
incf a2,f
incf neg_flag, f
a_pos
btfss b2,7
goto nextbit
comf b2,f
comf b1,f
incf b1,f
btfsc status, zero
incf b2,f
incf neg_flag, f
nextbit
rrf a2,f
rrf a1,f
btfss status, carry
goto nobit_l
movf b1,w
addwf res2,f
movf b2, w
btfsc status, carry
incfsz b2, w
addwf res3, f
btfsc status, carry
incf res4, f
bcf status, carry
nobit_l
btfss a1, 7
goto nobit_h
movf b1,w
addwf res3,f
btfsc status, carry
incf res4,f
movf b2,w
addwf res4,f
nobit_h
rrf res4,f
rrf res3,f
rrf res2,f
rrf res1,f
btfss status, carry
goto nextbit
btfss neg_flag, 0
goto no_invert
comf res4,f
comf res3,f
comf res2,f
comf res1,f
incf res1,f
btfsc status,zero
incf res2,f
btfsc status,zero
incf res3,f
btfsc status,zero
incf res4,f
no_invert |
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