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5.2 Instruction set and Addressing modes

5.2.1 Instruction format

The format of 8085 microprocessor instructions is shown in figure.

Operand

Opcode
Operand-1 Operand-2

8-bits 8-bits 8-bits

Figure : 5.7 Instruction format of 8085 microprocessor

The instruction has two parts, Opcode and Operand.

Opcode : Represents the operation to be performed on the operand. It is also
called mnemonic.
Operand : Data or address is given in this part. If the operand is an 8-bit data,
only Operand-1 is present in the instruction. If the operand is a 16-bit data or
address, Operand-1 and Operand-2 are specified in the instruction. Both
Operand-1 and Operand-2 are optional.

5.2.2 Classification of instructions based on size

There are three groups of instructions in 8085 microprocessor based on the
length or size of the instruction. They are,
1. Single byte (or 1 byte) instructions
2. Two byte instructions
3. Three byte instructions

Single byte instructions
Byte 1

D D D D D D D D
0
4
5
6
1
2
3
7

Opcode

This type of instruction has only Opcode and the operand is specified
within the Opcode itself.

Example : 1) MOV B, C ii) ADD B

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