Predecrement By 1; Address Register Indirect — Postincrement By Offset Nn - Motorola DSP56000 Manual

EXAMPLE: MOVE X1,X: (R2)+N2
BEFORE EXECUTION
X1
47 24 23
A 5 B 4 C 6
23 0 23
$3204
$3200
Assembler Syntax: (Rn)+Nn
Memory Spaces: P:, X:, Y:, XY:, L:
Additional Instruction Execution Time (Clocks): 0
Additional Effective Address Words: 0
Figure 4-7 Address Register Indirect — Postincrement by Offset Nn
an extra instruction cycle, cannot be used for making XY: memory references.
4.4.1.7

Predecrement By 1

The address of the operand is the contents of the address register, Rn, decremented by
1 before the operand address is used (see Table 4-1 and Figure 4-10). The contents of
Rn are decremented and stored in the same address register. This addressing mode re-
quires an extra instruction cycle. This mode cannot be used for making XY: memory
references, nor can it be used for modifying the contents of Rn without an associated data
MOTOROLA
ADDRESSING
X0
0
0 0 0 0 0 1
0
X MEMORY
23 0
X X X X X X
X X X X X X
15 0
R2 $3200
15 0
$0004
N2
15 0
M2 $FFFF
ADDRESS GENERATION UNIT
AFTER EXECUTION
X1
47 24 23
A 5 B 4 C 6 0 0
23 0 23
X MEMORY
23
$3204 X X X X X X
$ A 5 B 4 C 6
$3200
15
R2
15
N2
15
M2
X0
0
0 0 0 1
0
0
0
$3204
0
$0004
0
$FFFF
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