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 + IRm
Assembler Syntax:
*+ AR
n(IRm)
Modification Field:
01000
if
m = 0
10000
if
m = 1
(+)
0
0
31
24 23
Address
x
x
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 – IRm
Assembler Syntax:
*– AR
n(IRm)
Modification Field:
01001
if
m = 0
10001
if
m = 1
(–)
0
0
31
24 23
Address
x
x
AR
n
31
IR
m
x
0
31
Index
Operand
x
24
23