Computer Hardware User's Guide

Indirect Addressing
6-13 Addressing Modes
Example 6–11. Indirect Addressing With Preindex Add
The address of the operand to fetch is the sum of an auxiliary register (AR n )
and an index register (IR0 or IR1).
Operation: operand address = AR n + IR m
Assembler Syntax:*+AR n (IR m )
Modification Field: 01000 if m = 0
10000 if
m = 1
(+)
0
0
31 24 23
Addressxx
AR n
31
IR
m x
0
31
Index
Operand
x
24 23
Example 6–12. Indirect Addressing With Preindex Subtract
The address of the operand to fetch is the difference of an auxiliary register
(AR n ) and an index register (IR0 or IR1).
Operation: operand address = AR
n – IR m
Assembler Syntax: *–AR n (IR m )
Modification Field: 01001 if
m = 0
10001 if m = 1
(–)
0
0
31 24 23
Addressxx
AR n
31
IR
m
x
0
31
Index
Operand
x
24 23