Texas Instruments MSP430x1xx - Manual (Page 94)

Hardware Multiplier Operation
6-6
6.2.2 Multiply Signed, 16
×
16 bit, 16
×
8 bit, 8
×
16 bit, 8
×
8 bit
The following multiplication operation shows 36 bytes of program code and 36
execution cycles (16
×
16 bit multiplication).
**********************************************************
*
TRANSFER BOTH OPERANDS TO THE REGISTERS IN THE *
* HARDWARE MULTIPLIER MODULE *
* IF ONE OF THE OPERANDS IS 8 BIT, SIGN EXTENSION *
* is NEEDED. USE CONSTANT OPERAND1 AND OPERAND2 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
.BSS OPER1,2,200H
.BSS OPER2,2
.BSS RAM,8
.IF OPERAND1=0
MOV
&OPER1,&MPYS ; LOAD 1ST (WORD) OPERAND,
; DEFINES ADD. SIGNED MULTIPLY
.ELSE
MOV.B &OPER1,&MPYS ; LOAD 1ST (BYTE) OPERAND,
; DEFINES ADD. SIGNED MULTIPLY
SXT &MPYS ; EXPAND BYTE TO SIGNED WORD DATA
.ENDIF
.IF OPERAND2=0
MOV
&OPER2,&OP2 ; LOAD 2ND (WORD) OPERAND AND
; START SIGNED MULTIPLICATION
.ELSE
MOV.B &OPER2,&OP2
; LOAD 2ND (BYTE) OPERAND,
SXT &OP2 ; RE–LOAD 2ND OPERAND AND START
; SIGNED ‘FINAL’ MULTIPLICATION
.ENDIF
**********************************************************
*
EXAMPLE TO ADD THE RESULT OF THE HARDWARE *
* MULTIPLICATION TO THE RAM DATA, 64 BITS *
**********************************************************
ADD &RESLO,&RAM ; ADD LOW RESULT TO RAM
ADDC &RESHI,&RAM+2 ; ADD HIGH RESULT TO RAM+2
ADDC &SUMEXT,&RAM+4 ; ADD SIGN WORD TO EXTENSION WORD
ADDC &SUMEXT,&RAM+6 ; IF 64 BIT LENGTH IS USED