This document discusses different types of addressing modes used in computer systems to access memory locations. It describes basic addressing modes like immediate, register, direct, register indirect, and indexed addressing. It also covers special addressing modes such as relative, base, page, and indirect addressing that facilitate implementing language constructs and operating systems. The addressing mode specifies how the memory address is represented in an instruction to determine the operand location.

1. Addressing Modes

2. In order to access the memory, an address
must be provided.The manner in which the
address is specified in an instruction is called
the addressing mode. Addressing modes can
be categorized into:
 Basic addressing modes
 Special addressing modes
Addressing Modes

3. Basic Addressing Modes
Most computer systems use a number of basic
addressing modes to obtain operands from memory;
many high performance processors include additional
addressing modes consistent with the design
philosophies of the processor. Basic addressing modes
include:
 Implied addressing
 Immediate addressing
 Register Addressing
 Direct Addressing
 Register indirect addressing
 Implied register indirect addressing
 Indexed addressing

4. OPR
OPCODE
MPC
MDR
IR
Immediate addressing (microcomputers)
Basic Addressing Modes
OPCODE OPR OPCODE OPR
PC
Immediate addressing (large computers)
IR
IR OPR
Implied addressing
(implied)

5. Basic Addressing Modes
Reg.# 2IR Reg.# 2 (OPR)
Reg.# 1
Reg.# 3
Reg.# 4
Register addressing
OPCODE ADDR
OPR
M
PC
Direct addressing (large computers)
OPCODE
ADDR
OPR
M
MAR
PC
Direct addressing (microcomputers)

6. Basic Addressing Modes
Reg. # 1
Reg. # 2
Reg. # 3
OPR
M
OPCODE Reg. #2IR
Register indirect addressing
Reg. # 2 OPR
M
OPCODEIR
(implied)
Implied register indirect addressing
OPCODE Reg. # 2
Index
Reg. # 3
Reg. # 2
Reg. # 2
OPR
M
IR
Indexed addressing

7. Special Addressing Modes
Many processors have additional or special addressing
modes that facilitate ease implementing language
constructs and primitives often used in operating
systems and other systems programming environments.
Special addressing modes include:
 Relative addressing
 Base addressing
 Page addressing
 Indirect addressing

8. Special Addressing Modes
OPCODE offset
PC
offset
OPR
M
IR
Relative addressing
Specified address
Base register
OPR
M
Base addressing

9. Special Addressing Modes
Page EA OPR
M
Page addressing
Page register
ADDR
OPR
M
EA
Indirect addressing

10. Special Addressing Modes
Page EA OPR
M
Page addressing
Page register
ADDR
OPR
M
EA
Indirect addressing