Microprocessor instruction format of 8086

Microprocessor instruction format

1. Instruction Format in 8086 Overview of 8086 Instruction Types and Formats Your Name/Institution

2. Introduction to Instruction Formats • 8086 instructions vary in length from 1 to 6 bytes. • Each instruction consists of fields like opcode (operation code) and operand fields. • The opcode indicates the type of operation.

3. 1-Byte Instructions • Instructions are one byte long. • May have implied data or register operands. • Example: CLC (Clear Carry Flag).

4. Register-to-Register Format • This format is 2 bytes long. • The first byte specifies the operation and operand width. • The second byte contains register information (source and destination). • Example: MOV CL, AL (transfer data from AL to CL).

5. Register/Memory Without Displacement • Similar to register-to-register format but involves memory. • No displacement, address is provided via the R/M field. • Example: MOV AX, [BX] (transfer data from memory address in BX to AX).

6. Register/Memory With Displacement • Includes 1 or 2 extra bytes for displacement. • Allows for 8-bit or 16-bit displacement. • Example: MOV AX, [BX + 05] (transfer data from memory address in BX plus a 5-byte offset to AX).

7. Immediate Operand to Register • Format includes immediate data in the instruction itself. • Instruction length varies based on data size (3 or 4 bytes). • Example: MOV AX, 1234H (move immediate data 1234H into AX register).

8. Immediate Operand to Memory with Displacement • Requires 5 to 6 bytes for encoding. • Includes OPCODE, MOD, and R/M fields, with displacement and immediate data. • Example: MOV [5000H], 1234H (move immediate data 1234H to memory location 5000H).