Microprocessor Instruction Sets

The immediate data in a MOV instruction is always variable data.

The opcode in a MOV instruction is always followed by a register address.

The MOV EAX, 13456H instruction copies data from memory location 13456H to EAX.

The symbol # is used to represent immediate data in all assemblers.

Immediate addressing operates on a byte or word of data.

The MOV AX, 3456H instruction is an example of register addressing.

Immediate data are always transferred from a register or memory location.

The opcode in a MOV instruction is always 1 byte long.

The MOV EAX, 13456H instruction is an example of opcode addressing.

The # symbol is used to represent register addresses in some assemblers.

Data Addressing Modes

MOV instruction is a common and flexible instruction that provides a basis for explanation of data-addressing modes.
The direction of data flow is from the source (right) to the destination (left), next to the opcode MOV.

Register Addressing

Register addressing is the most common form of data addressing.
The microprocessor contains 8-bit register names used with register addressing: AH, AL, BH, BL, CH, CL, DH, and DL.
16-bit register names used with register addressing: AX, BX, CX, DX, SP, BP, SI, and DI.

Direct Addressing

Direct addressing with a MOV instruction transfers data between a memory location and the AL (8-bit), AX (16-bit), or EAX (32-bit) register.
Direct addressing usually uses a 3-byte long instruction.
Example: MOV AL,DATA loads AL from the data segment memory location DATA (1234H).

Immediate Addressing

Immediate addressing implies that data immediately follow the hexadecimal opcode in the memory.
Immediate data are constant data, unlike data transferred from a register or memory location, which are variable data.
Immediate addressing operates upon a byte or word of data.
Example: MOV EAX,13456H instruction copies the immediate data (13456H) into EAX.

Understand the MOV instruction and its role in data addressing modes. Learn about the direction of data flow and the function of opcodes in microprocessors.