Fundamentals of Addressing Modes

Addressing Modes is the way in which the argument of an instruction is specified. The addressing mode defines a rule for interpreting the address field of the instruction before the operand is reached. Addressing mode is used in instructions which operate on the data or in instructions which change the program flow.

Data in the memory can be accessed using different addressing modes.

Operands can be of one of the following: register, immediate, direct memory, and indirect memory.

An immediate operand is a constant or the result of a constant expression. The assembler encodes immediate values into the instruction at assembly time. Operand of this type is always at the source side.

A direct memory operand specifies the data at a given address. Address can be given in numerical form or as an variable. It can be closed in brackets to show that the contents, not the address, is used.