Texas Instruments MSP430x1xx - Manual (Page 409)

Instruction Set Overview
B-59 Instruction Set Description
SXT Extend Sign
Syntax SXT dst
Operation Bit 7 –> Bit 8 ......... Bit 15
Description The sign of the low byte is extended into the high byte as shown in Figure B–11.
Status Bits N: Set if result is negative, reset if positive
Z: Set if result is zero, reset otherwise
C: Set if result is not zero, reset otherwise (.NOT. Zero)
V: Reset
Mode Bits OscOff, CPUOff, and GIE are not affected.
Figure B–11. Destination Operand Sign Extension
15 8 7 0
Example R7 is loaded with the Timer/Counter value. The operation of the sign-extend
instruction expands bit 8 to bit 15 with the value of bit 7.
R7 is then added to R6.
MOV.B &TCDAT,R7 ; TCDAT = 080h: . . . . . . . . 1000 0000
SXT R7 ; R7 = 0FF80h: 1111 1111 1000 0000
ADD R7,R6 ; add value of EDE to 16-bit ACCU