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 Codeโ€“ It is the task to be performed. It is also called op-code.
  • Operandโ€“ It is the data to be operated on.
instruction set of 8085

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, โ€œbyteโ€ and โ€œwordโ€ 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-

TaskOpcodeOperandBinary CodeHex Code
Copy the contents of accumulator in the register CMOVC,A0100 11114FH
Add the content of register B to AccumulatorADDB1000 000080H
Invert each bit the AccumulatorCMA0010 11112FH

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-

TaskOpcodeOperandBinary CodeHex code
Load an 8-bit data byte in the AccumulatorMVIA, 32H0011 1110
0011 0010
Load an 8-bit data byte in register BMVIB, F2H0000 0110
1111 0010

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.

TaskOpcodeOperandBinary CodeHex code
Load content of memory 2050H into ALDA2050H0011 1010
0101 0000
0010 0000
Transfer the program sequence to memory location 2085H.JMP2085H1100 0011
1000 0101
0010 0000
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