dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 156

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

Data Arithmetic Logic Unit
Limiting does not occur for move instructions that specify one portion of an accumulator as the source
operand.
When FF2 is written, it receives the low-order portion of the word; the high-order portion is not used. See
Figure 5-7. When FF2 is read, the register contents occupy the low-order portion (bits 3–0) of the word;
the high-order portion (bits 15–4) is sign extended. See Figure 5-8 on page 5-11.
5-10
Writing the FF2 Portion:
Writing the FF1 Portion:
Writing the FF0 Portion:
A
A
A
Register FF2 Used
as a Destination
35 32 31
35 32 31
35 32 31
A2
A2
A2
X
X
X
X
X
X
Figure 5-7. Writing the Accumulator Extension Registers (FF2)
Before Execution
Before Execution
Before Execution
X
X
X
A1
A1
A1
X
X
X
Figure 5-6. Writing the Accumulator by Portions
MOVE.W #$ABCD,A2
MOVE.W #$1234,A1
MOVE.W #$A987,A0
X
X
X
16 15
16 15
16 15
DSP56800E Core Reference Manual
X
X
X
X
X
X
A0
A0
A0
15
15
X
X
X
No Bits Present
Not Used
X
X
X
0
0
0
A
A
A
4 3
4 3
35 32 31
35 32 31
35 32 31
LSB of
A2
A2
A2
Word
D
X
X
FF2
X
1
X
0
0
After Execution
X
After Execution
2
After Execution
X
CDBR Bus Contents
Register FF2
A1
A1
A1
X
3
X
X
16 15
4
16 15
X
16 15
Freescale Semiconductor
X
X
A
X
X
9
A0
A0
A0
X
X
8
X
X
7
0
0
0