Texas Instruments MSP430x1xx - Manual (Page 96)

Hardware Multiplier Operation
6-8
6.2.4 Multiply Signed and Accumulate, 16x16bit, 16x8bit, 8x16bit, 8x8bit
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* TRANSFER BOTH OPERANDS TO THE REGISTERS IN THE HARDWARE *
* MULTIPLIER MODULE *
* USE CONSTANT OPERAND1 AND OPERAND 2 TO IDENTIFY BYTE DATA *
********************************************************************
OPERAND1
.EQU 0 ; 0: OPERAND1 IS WORD (16BIT)
; 8: OPERAND1 IS BYTE ( 8BIT)
OPERAND2 .EQU 0 ; 0: OPERAND2 IS WORD (16BIT)
; 8: OPERAND2 IS BYTE ( 8BIT)
MPY .EQU 0130H
MPYS .EQU 0132H
MAC .EQU 0134H
MACS .EQU 0136H
OP2 .EQU 0138H
RESLO .EQU 013AH
RESHI .EQU 013CH
SUMEXT .EQU 013EH
MAXMACS .EQU 32H ;NUMBER OF MACS FUNCTIONS WHICH COULD
;BE EXECUTED TILL AN OVERFLOW OR UNDERFLOW
;COULD OCCUR THE FIRST TIME
.BSS OPER1,2,200H
.BSS OPER2,2
.BSS RAM,8
.BSS MCOUNT,2
.IF OPERAND1=8
MOV.B &OPER1,&MACS ; LOAD 1ST OPERAND,
; DEFINES ADD. UNSIGNED MULTIPLY
SXT &MACS ; EXPAND BYTE TO SIGNED WORD DATA
.ELSE
MOV &OPER1,&MACS ; LOAD 1ST OPERAND,
; DEFINES ADD. UNSIGNED MULTIPLY
.ENDIF
.IF OPERAND1=8
SXT &OPER2 ; OPER2 MEMORY LOCATION NEEDS
; 2 BYTES
MOV.B &OPER2,&OP2 ; LOAD 2ND OPERAND AND START
; MULTIPLICATION
.ELSE
MOV &OPER2,&OP2 ; LOAD 2ND OPERAND AND START
; MULTIPLICATION
.ENDIF
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* EXAMPLE TO ADD THE RESULT OF THE HARDWARE MULTIPLICATION *
* TO THE RAM DATA IF NECESSARY *
* THE RESULT OF THE MULTIPLICATION IS HELD IN RESLO AND *
* RESHI REGISTERS. THE UPPER TWO WORDS IN THE EXAMPLE ARE *
* FURTHER LOCATED IN THEIR RAM LOCATION *
********************************************************************
INC MCOUNT ; INC MACS COUNTER
CMP #MAXMACS,MCOUNT ; ONLY ADD TO RAM IF NECESSARY
JNE NEXTMACS ;
ADDC &RESLO,&RAM+0 ; ADD SUMEXTENSION TO RAM+0
ADDC &RESHI,&RAM+2 ; ADD SUMEXTENSION TO RAM+2
ADDC &SUMEXT,&RAM+4 ; ADD SUMEXTENSION TO RAM+4
ADDC &SUMEXT,&RAM+6 ; IF 64 BIT LENGTH IS USED
CLR MCOUNT
NEXTMACS
. . .