Microprocessor Instruction Sets

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.