Displacement addressing combines direct and register indirect addressing by using an effective address that is the sum of a memory address and the contents of a register plus a displacement value. It provides flexibility but also complexity. For example, if a register contains 20 and the displacement is 2, the effective address is the memory address 1001 plus the register value 20 plus the displacement 2, for a total of 1003. The main uses of displacement addressing are relative addressing using the program counter, base-register addressing where the register contains a base memory address, and indexing where the register provides an offset from a memory address.

1. Displacement Addressing
By Mourin Mondol [152-35-1298]

2. What is
displacement
addressing?
A very powerful mode of
addressing combines the
capabilities of direct
addressing and register
indirect addressing.

3. EA = A + (R)where,
A = Memory address
R = Register address
EA = Effective address

4. Why & Why not?
Flexibility Complexity
● When we need flexibility we should use it.
● Otherwise for its complexity we should avoid this.

5. Example:
5
1000 1001 1002 1003 1004
Register Address: 20
Displacement =2
…..
Register
Displacement=2
Effective Address=1001+2 =1003
1000 1001 1002 1003 1004 1005Memory
10 20 30 40 50

6. 3 COMMON
USES
● RELATIVE ADDRESSING
● BASE-REGISTER
● INDEXING
[Relative]: referenced register is
the program counter (PC)
[Base-register]: referenced register
contains a main memory
address and the address field
contains a displacement from
that address.
[Indexing]: address field references
a main memory address, and
referenced register contains a
positive displacement from that
address.

7. Any Questions?