dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 53

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

Figure 3-6 shows the result of writing values to each portion of the accumulator. Note that only the portion
specified in the instruction is modified; the other two portions remain unchanged.
See Section 3.2, “Accessing the Accumulator Registers,” for a discussion of when it is appropriate to
access an accumulator by its individual portions and when it is appropriate to access it as an entire
accumulator.
Freescale Semiconductor
Writing the F2 Portion Example
Writing the F1 Portion Example
Writing the F0 Portion Example
A
A
A
Used as a Source
Register F2
35 32 31
35 32 31
35 32 31
A2
A2
A2
X
X
X
X
X
X
Before Execution
Before Execution
Before Execution
X
X
X
Figure 3-5. Reading the Accumulator Extension Registers (F2)
A1
A1
A1
X
X
X
Figure 3-6. Writing the Accumulator by Portions
X
X
X
16 15
16 15
16 15
X
X
X
: MOVE #$ABCD,A2
: MOVE #$1234,A1
: MOVE #$A987,A0
X
X
X
A0
A0
A0
15
15
Data Arithmetic Logic Unit
Sign Extension
No Bits Present
X
X
X
of F2
X
X
X
0
0
0
A
A
A
4 3
4 3
Contents
4 LSB of
35 32 31
35 32 31
35 32 31
Word
A2
A2
A2
of F2
D
X
X
F2
X
1
X
0
0
After Execution
After Execution
After Execution
Accessing the Accumulator Registers
X
2
X
Register F2
CGDB Bus Contents
A1
A1
A1
X
3
X
X
16 15
4
16 15
X
16 15
X
X
A
X
X
9
A0
A0
A0
X
X
8
X
X
7
0
0
0
3-9