dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 157

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

Although the FF1 portion of every accumulator is accessible by all instructions, the FF2 and FF0 portions
are only accessible for the A and B registers. The C2, C0, D2, and D0 accumulator portions are only
accessible through a limited set of instructions:
There are no other ways to read or write these accumulator portions directly. To read or write the values of
C2 and D2, use the code in Example 5-4 and Example 5-5 (or similar code).
Freescale Semiconductor
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MOVE.W #xxxx,<register>
BFCHG, BFCLR, BFSET, ANDC, ORC, EORC, NOTC
BFTSTH, BFTSTL
BRSET, BRCLR
Push register to stack (C2 and D2 only)
Pop register from stack (C2 and D2 only)
Used as a Source
Register FF2
; First technique, with sign extension
ASR16
MOVE.W
; Second technique, no sign extension
LSR16
MOVE.W
; First technique
MOVE.W
ASL16
; Second technique
MOVE.W
ASL16
; Third technique (may saturate if SA = 1)
MOVE.W
TFR
Figure 5-8. Reading the Accumulator Extension Registers (FF2)
Example 5-4. Reading the Contents of the C2 Register
C,X0
X0,R0
C,A
A1,R0
R2,C1
C
R2,A1
A,C
R3,A2
A,C
Example 5-5. Writing a Value into the C2 Register
Data Arithmetic Logic Unit
15
15
; Shift C2 into X0 with sign extension
; Write C2 signed contents to final destination
; Shift C2 into A1 with no sign extension
; Write C2 unsigned contents to final destination
; Write value first to C1
; Shift the C1 register into C2
; Write value first to A1
; Shift the A1 register into C2
; Write value first to A2
; Transfer value from A to C accumulator
Sign Extension
No Bits Present
of FF2
4 3
4 3
Contents
LSB of
of FF2
Word
FF2
Accessing the Accumulator Registers
0
0
Register FF2
CDBW Bus Contents
5-11