Instruction Format

Instruction : A statement that tells a computer to do something.

Instruction Format:The way an instruction is written.

An instruction in a computer comprises of groups called fields.The most common fields are:

1. Operation Field

• Opcode

• Specifies the operation to be performed by the instruction

  Eg:ADD,SUB,MOV,etc.

• It can be a value or register number on which the operation is performed.

• Mandatory part of every instruction.

2. Address Field

• Adress of operand/Operand Reference

• Refers to a location (address) where the operand is stored.

• The address may be a memory address or a register address.

TYPES OF INSTRUCTION FORMATS

1.Zero Address Instruction Format

• There is no address field.
• Stack is used.

2. One Address Instruction Format

• This instruction format uses only one address field.

• The other operand is stored on Accumulater Register.

3. Two Address Instruction Format

• It uses two address fields.

• Most commonly used instruction format.

• Example instructions are ADD,MUL,MOV

4. Three Address Instruction Format

• It uses three instruction fields.