Computer Hardware User's Guide
Indirect Addressing
6-9
Addressing Modes
Example 6–3. Indirect Addressing With Predisplacement Add
The address of the operand to fetch is the sum of an auxiliary register (AR
n
) and
the displacement (
disp
). The displacement is either an 8-bit unsigned integer
contained in the instruction word or an implied value of 1.
Operation: operand address = AR
n
+
disp
Assembler Syntax: *+AR
n
(
disp
)
Modification Field: 00000
(+)
0
0
31 24 23
Addressx
AR
n
31
disp
00
0
31
87
Integer
Operand
0...0
x
Example 6–4. Indirect Addressing With Predisplacement Subtract
The address of the operand to fetch is the contents of an auxiliary register
(AR
n
) minus the displacement (
disp
). The displacement is either an 8-bit
unsigned integer contained in the instruction word or an implied value of 1.
Operation: operand address = AR
n
–
disp
Assembler Syntax: *–AR
n
(
disp
)
Modification Field: 00001
(–)
0
0
31 24 23
Addressxx
AR
n
31
disp
00
0
31
87
Integer
Operand
0...0