8085 Instruction Set: Part 1

Introduction

The 8085 microprocessor, developed by Intel, has a rich set of instructions that allow it to perform a wide range of operations. These instructions can be broadly classified into several categories, each serving a specific purpose in the operation of the microprocessor. Understanding these instructions is crucial for programming the 8085 effectively.

Categories of Instructions

The 8085 instruction set can be divided into the following categories:

1. Data Transfer Instructions
2. Arithmetic Instructions
3. Logical Instructions
4. Branch Instructions
5. Stack, I/O, and Machine Control Instructions

1. Data Transfer Instructions

Data transfer instructions are used to move data between registers, between memory and registers, or between I/O ports and the accumulator. These instructions do not alter the data being transferred.

Common Data Transfer Instructions:

2. Arithmetic Instructions

Arithmetic instructions perform arithmetic operations such as addition, subtraction, increment, and decrement on the data in registers or memory.

Common Arithmetic Instructions:

3. Logical Instructions

Logical instructions perform bitwise logical operations such as AND, OR, XOR, and complement on the data in registers or memory.Common Logical Instructions:

Examples of Data Transfer Instructions

1. MOV Instruction:
   • MOV A, B: Copies the contents of register B into register A.
   • MOV M, A: Copies the contents of the accumulator into the memory location pointed by the H-L pair.
2. MVI Instruction:
   • MVI A, 0x32: Loads the immediate value 0x32 into register A.
   • MVI M, 0x45: Loads the immediate value 0x45 into the memory location pointed by the H-L pair.
3. LDA and STA Instructions:
   • LDA 2500H: Loads the contents of memory location 2500H into the accumulator.
   • STA 2500H: Stores the contents of the accumulator into memory location 2500H.
4. LXI Instruction:
   • LXI H, 2500H: Loads the immediate value 2500H into the H-L pair.
5. LDAX and STAX Instructions:
   • LDAX B: Loads the contents of the memory location pointed by the B-C pair into the accumulator.
   • STAX D: Stores the contents of the accumulator into the memory location pointed by the D-E pair.

Examples of Arithmetic Instructions

1. ADD Instruction:
   • ADD B: Adds the contents of register B to the accumulator.
2. ADI Instruction:
   • ADI 0x12: Adds the immediate value 0x12 to the accumulator.
3. SUB Instruction:
   • SUB C: Subtracts the contents of register C from the accumulator.
4. SUI Instruction:
   • SUI 0x10: Subtracts the immediate value 0x10 from the accumulator.
5. INR and DCR Instructions:
   • INR A: Increments the contents of register A by one.
   • DCR B: Decrements the contents of register B by one.
6. INX and DCX Instructions:
   • INX H: Increments the contents of the H-L pair by one.
   • DCX D: Decrements the contents of the D-E pair by one.
7. DAD Instruction:
   • DAD B: Adds the contents of the B-C pair to the H-L pair.

Summary

In this part of the reading material, we have covered the first three categories of the 8085 instruction set: Data Transfer Instructions, Arithmetic Instructions, and Logical Instructions. These instructions form the core of the operations that the 8085 microprocessor can perform, allowing it to manipulate data, perform calculations, and execute logical operations.In the next part, we will explore the remaining categories: Branch Instructions and Stack, I/O, and Machine Control Instructions. Understanding these instructions will provide a comprehensive view of the capabilities of the 8085 microprocessor.

To enhance understanding, below are the lecture videos that may help in completing the lab assignment.