dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 627

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

SXT.B
Operation:
S[7] → D[MSB:8]
S[7:0] → D[7:0]
Description: Sign extend a byte that is located in the source register, and place the extended value into the destina-
Usage:
Example:
Explanation of Example:
Condition Codes Affected:
Instruction Fields:
Instruction Opcodes:
Timing:
Memory:
Freescale Semiconductor
SXT.B
Operation
SXT.B
Before Execution
FFF,FFF
A2
C
X0
tion (D). If the destination register is an accumulator, the value is aligned such that the original byte
value is located in the low-order 8 bits of the MSP of the destination accumulator (or Y register). If the
source is a 16-bit register, it is internally concatenated with 16 zero bits to form a 32-bit value. The
upper 8 bits of this value corresponds to the sign extension from bit 23 and then moved to the destina-
tion. If the destination is a 16-bit register, only the upper 16 bits of this value are stored. The result is
not affected by the state of the saturation bit (SA).
SXT.B can be used to sign extend a 24-bit value into an accumulator by using the Y register as the
source for the operation.
SXT.B
Initially, the A accumulator holds the value $C:26A7:1A36, and the X0 register holds $81F3. The byte
in X0 is sign extended to form the 32-bit value $FFF3:0000 and stored in the A accumulator (with
4 bits sign extension).
The condition codes are not affected by this instruction.
1 oscillator clock cycle
1 program word
(no parallel move)
(no parallel move)
26A7
81F3
A1
X0,A
Operands
FFF,FFF
FFF
1A36
A0
15
Sign Extend Byte
0
Instruction Set Details
1
; sign extend byte in X0 and place in A
C
1
1
1
Assembler Syntax:
SXT.B
W
12
1
1
1
Sign extend byte. When the destination is the Y regis-
ter or an accumulator, the LSP portion is cleared if the
source is a 16-bit register.
11
An alternate syntax for the preceding instruction if the
1
After Execution
A2
F
X0
1
source and the destination are the same.
F
S,D
FFF3
F
81F3
8
A1
F
7
(no parallel move)
Comments
b
b
0000
b
4
A0
0
3
SXT.B
0
1
A-283
1
0