8086 Assembly Language Addressing Modes

Memory Addressing in 8086 Assembly Language

Addressing Modes

• Immediate Addressing: The address is specified directly in the instruction. Example: MOV AX, 100
• Register Addressing: The address is stored in a register. Example: MOV AX, BX
• Direct Addressing: The address is specified directly in the instruction. Example: MOV AX, [100]
• Indirect Addressing: The address is stored in a register or memory location. Example: MOV AX, [BX]
• Indexed Addressing: The address is calculated using a base register and an index register. Example: MOV AX, [BX+SI]

Memory Segments

• Code Segment (CS): Stores the program's code
• Data Segment (DS): Stores the program's data
• Extra Segment (ES): Used for extra data
• Stack Segment (SS): Used for the program's stack
• Segment Registers: CS, DS, ES, and SS registers store the starting address of each segment

Memory Address Calculation

• Segment:Offset format: Segment:Register or Segment:Immediate
• Effective Address (EA): Calculated using the segment base address and the offset address
• 20-Bit Addressing: 8086 uses 20-bit addresses, divided into 16-bit segment and 16-bit offset

Memory Access Instructions

• MOV: Moves data between registers, memory, and immediates
• LEA: Loads the effective address of a memory location into a register
• LDS/LES: Loads the DS/ES register with the segment address and the specified register with the offset address

Memory Models

• Small Memory Model: One segment for code and data (64KB)
• Compact Memory Model: Multiple segments for code and data (up to 64KB each)
• Large Memory Model: Separate segments for code and data (up to 64KB each)

Addressing Modes

• Immediate Addressing uses the address specified directly in the instruction.
• Register Addressing uses the address stored in a register.
• Direct Addressing uses the address specified directly in the instruction.
• Indirect Addressing uses the address stored in a register or memory location.
• Indexed Addressing calculates the address using a base register and an index register.

Memory Segments

• Code Segment (CS) stores the program's code.
• Data Segment (DS) stores the program's data.
• Extra Segment (ES) is used for extra data.
• Stack Segment (SS) is used for the program's stack.
• Segment Registers (CS, DS, ES, and SS) store the starting address of each segment.

Memory Address Calculation

• Memory addresses are in Segment:Offset format.
• The Effective Address (EA) is calculated using the segment base address and the offset address.
• 8086 uses 20-bit addresses, divided into 16-bit segment and 16-bit offset.

Memory Access Instructions

• MOV moves data between registers, memory, and immediates.
• LEA loads the effective address of a memory location into a register.
• LDS/LES loads the DS/ES register with the segment address and the specified register with the offset address.

Memory Models

• Small Memory Model uses one segment for code and data (64KB).
• Compact Memory Model uses multiple segments for code and data (up to 64KB each).
• Large Memory Model uses separate segments for code and data (up to 64KB each).