Prerequisite – Addressing Modes
1. Direct Addressing Mode:
In direct addressing mode, the address field contains the address of the operand.
Effective Address (EA) = address field of operand
Example: Add the contents of register 1001 to the accumulator.
Only a single memory reference is required to access data. So no additional calculations are required to work out effective address.
2. Immediate Addressing Mode:
In immediate addressing mode, the operand is a part of the instruction.
Here the Operand = Address Field
Example: Add 5 to the accumulator.
No memory reference is required to fetch data. So no additional calculations are required to work out the effective address. It is a fast method. But the downside is that it has a limited range.
Now let’s compare Direct and Immediate addressing modes.
|Direct Addressing Mode||Immediate Addressing Mode|
|Address fields contains the effective address of operand||There is no address field as the operand is a part of the instruction.|
|It requires one reference to memory.||It does not require any reference to memory.|
|It is slower compared to immediate mode.||It is a faster process.|
|It has more range than in immediate mode.||It has a limited range.|
|Example: Add (1001)||Example: ADD 5|