Motorola DSP56000 Manual: Address Register Indirect — Predecrement

24-bit.

EXAMPLE: MOVE X: –(R5),B1
BEFORE EXECUTION
B2
B1
55 48 47
3
B B
6
2
D 0
7
0 23
\$3007
\$3006
Assembler Syntax: –Rn
Memory Spaces: P:, X:, Y:, L:
Additional Instruction Execution Time (Clocks): 2
Figure 4-10 Address Register Indirect — Predecrement
DSP56K. The MMMM column indicates the hex value which should be stored in the Mn
register.
4.4.2.1
Linear Modifier (Mn=\$FFFF)
When the value in the modifier register is \$FFFF, address modification is performed using
normal 16-bit linear arithmetic (see Table 4-2). A 16-bit offset, Nn, and + 1 or –1 can be
used in the address calculations. The range of values can be considered as signed (Nn
from –32,768 to + 32,767) or unsigned (Nn from 0 to + 65,535) since there is no arithmetic
4 - 16
B0
24 23
0
4 A
5
5
4
C
0
0 23
0
X MEMORY
23
0
\$ A B C D E F
\$ 1 2 3 4 5 6
15
0
R5
\$3007
15
0
N5
XXXX
15
0
M5
\$FFFF
AFTER EXECUTION
B2
B1
55 48 47
24 23
3
B
1
2 3
4
5
6 A
7
0 23
0 23
23
\$3007
\$3006
B0
0
5 5
4
C
0
0
X MEMORY
0
\$ A B C D E F
\$ 1 2 3 4 5 6
15
0
R5
\$3006
15
0
N5
XXXX
15
0
M5
\$FFFF
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