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:
- Data Transfer Instructions
- Arithmetic Instructions
- Logical Instructions
- Branch Instructions
- 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:
| Opcode | Operand | Description |
|---|---|---|
| MOV | Rd, Rs | Copy the contents of the source register (Rs) to the destination register (Rd). |
| MOV | Rd, M | Copy the contents of the memory location pointed to by the HL pair to the destination register (Rd). |
| MOV | M, Rs | Copy the contents of the source register (Rs) to the memory location pointed to by the HL pair. |
| MVI | Rd, Data | Move immediate 8-bit data to the destination register (Rd). |
| MVI | M, Data | Move immediate 8-bit data to the memory location pointed to by the HL pair. |
| LXI | Reg. pair, 16-bit data | Load immediate 16-bit data into the register pair. |
| LDA | 16-bit address | Load the contents of the specified memory location into the accumulator. |
| STA | 16-bit address | Store the contents of the accumulator into the specified memory location. |
| LHLD | 16-bit address | Load H and L registers directly from the specified memory locations. |
| SHLD | 16-bit address | Store H and L registers directly into the specified memory locations. |
| LDAX | B/D | Load the accumulator indirectly from the memory location pointed to by the specified register pair (B or D). |
| STAX | B/D | Store the contents of the accumulator into the memory location pointed to by the specified register pair (B or D). |
| XCHG | None | Exchange the contents of the H and L registers with the contents of the D and E registers. |
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:
| Opcode | Operand | Description |
|---|---|---|
| ADD | R | Add the contents of the specified register (R) to the accumulator. |
| ADD | M | Add the contents of the memory location pointed to by the HL pair to the accumulator. |
| ADI | Data | Add immediate 8-bit data to the accumulator. |
| ADC | R | Add the contents of the specified register (R) to the accumulator along with the carry flag. |
| ADC | M | Add the contents of the memory location pointed to by the HL pair to the