user manual

ADDRESSING
MOTOROLA ADDRESS GENERATION UNIT 4 - 11
Rn without an associated data move.
4.4.1.5 Postdecrement By Offset Nn
The address of the operand is in the address register, Rn (see Table 4-1 and Figure 4-8).
After the operand address is used, it is decremented by the contents of the Nn register
and stored in the same address register. The contents of the Nn register are unchanged.
This mode cannot be used for making XY: memory references, but it can be used to mod-
AF654321FEDCBA
15 0
15 0
15 0
EXAMPLE: MOVE B0,Y: (R1)+
BEFORE EXECUTION AFTER EXECUTION
B2 B1 B0
55 48 47 24 23 0
7 0 23 0 23 0
Y MEMORY
23 0
XXXXXX
$2500
Y MEMORY
23 0
$2500
$2500
XXXX
$FFFF
R1
N1
M1
15 0
15 0
15 0
$2501
XXXX
$FFFF
R1
N1
M1
Assembler Syntax: (Rn)+
Memory Spaces: P:, X:, Y:, XY:, L:
Additional Instruction Execution Time (Clocks): 0
Additional Effective Address Words: 0
$FEDCBA
AF654321FEDCBA
B2 B1 B0
55 48 47 24 23 0
7 0 23 0 23 0
XXXXXX
$2501
XXXXXXX
$2501
Figure 4-5 Address Register Indirect — Postincrement