
Instruction Set Description
4.6.2.49 SXT
SXT
Extend sign
SXT dst
Syntax
Operation
dst.7
→
dst.15:8, dst.7
→
dst.19:8 (register mode)
Description
Register mode: the sign of the low byte of the operand is extended into the bits
Rdst.19:8.
Rdst.7 = 0: Rdst.19:8 = 000h afterwards
Rdst.7 = 1: Rdst.19:8 = FFFh afterwards
Other modes: the sign of the low byte of the operand is extended into the high byte.
dst.7 = 0: high byte = 00h afterwards
dst.7 = 1: high byte = FFh afterwards
Status Bits
N:
Set if result is negative, reset otherwise
Z:
Set if result is zero, reset otherwise
C:
Set if result is not zero, reset otherwise (C = .not.Z)
V:
Reset
Mode Bits
OSCOFF, CPUOFF, and GIE are not affected.
Example
The signed 8-bit data in EDE (lower 64 K) is sign extended and added to the 16-bit
signed data in R7.
MOV.B
&EDE,R5
; EDE -> R5. 00XXh
SXT
R5
; Sign extend low byte to R5.19:8
ADD
R5,R7
; Add signed 16-bit values
Example
The signed 8-bit data in EDE (PC +32 K) is sign extended and added to the 20-bit data
in R7.
MOV.B
EDE,R5
; EDE -> R5. 00XXh
SXT
R5
; Sign extend low byte to R5.19:8
ADDA
R5,R7
; Add signed 20-bit values
182
CPUX
SLAU272C – May 2011 – Revised November 2013
Copyright © 2011–2013, Texas Instruments Incorporated