ADDRESSING MODES

6.1 Addressing Modes: introduction
Addressing modes are an aspect of the instruction set
architecture in most CPU designs. The various addressing
mode helps to identify the type of operands in the instruction.
An addressing mode specifies how to calculate the effective
memory address of an operand by using information held in
registers and/or constants contained within a machine
instruction or elsewhere. It is one of the important
threads( المواض يع ) that attract full attention of compiler writers
and those who programmed using assembly language directly.
Be think with the following instructions:
add R1,x
add R1,500
add R1,[x]
What is the similarity of these instructions?
The answer is: all of these instructions implement adding
operation on R1 and all of them have two addresses.
Now ,What is the difference among the three instructions?
The answer is: the value that added to R1.
In the first instruction the value stored in a memory address
called (X) , here the CPU has one visit to the memory .