Instruction set of 8085

In diploma engineering notes, this is the important topic of 8051. Poly Notes Hub shares a topic in about the instruction set of 8085 microprocessor.

What is Instruction set?

An instruction is a command to the microprocessor or microcontroller to perform a given task on specific data.

Each instruction has two parts:

• Operation Code– It is the task to be performed. It is also called op-code.
• Operand– It is the data to be operated on.

Instruction set word size

The 8085 microprocessor instruction set is classified into the following three groups according to the word size or byte size.

In 8085, “byte” and “word” are synonymous because it is an 8-bit microprocessor. However, instructions are commonly referred to in terms of bytes rather than words.

1. 1-byte instruction
2. 2-byte instruction
3. 3-byte instruction

One-byte instruction set of 8085

A 1-byte instruction includes the opcode and the operand in the same byte. For example-

Two-byte instruction set of 8085

In 2-byte instruction, the first byte specifies the operation code and the second byte specifies the operand. For example-

Three-byte instruction set of 8085

In a 3-byte instruction, the first byte specifies the opcode, and the following two bytes specifies the 16-bit address. Note that the second byte is the low-order address and the third byte is the high-order address.