What is instruction set? Explain various Kinds of instructions of 8086 microprocessor.


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An instruction of a computer is a command given to the computer to perform a specified operation on given data. In microprocessor, the instruction set is the collection of the instructions that the microprocessor is designed to execute.

Data Transfer Instruction

This group includes the instructions used for moving the data from one place to another. In data transfer group of instructions data or address can be transferred to either register, memory or I/O ports. The source holds either the immediate data, register or memory location. While the destination holds either the address of any memory location or register. Example:instruction 1

The data present in register 1 is transferred to register 2 or memory location given in the operand.

Arithmetic Instructions

These instructions are used in order to execute arithmetic instructions like addition, subtraction, multiplication, division, increment or decrement.

The flags of the 8086 microprocessor are altered when arithmetic and logical instructions are executed. Basically, the status of the result of the operations is reflected by the flag. Example:

instruction 17

The data in the two registers are added and output is stored in register 2.

Logical Instructions

These instructions perform operations like AND, OR, complement, shift and rotate on the binary data. The outcome of the operation executed by logical instructions is represented as the status of flag register. Example:

instruction 42

AND operation over each bit of two registers is performed and register 2 stores the result.

String Manipulation Instruction

A sequence of bytes or words forms a string. This instruction set contains instructions for movement, comparison, scanning, loading or storing of the string. Example:

instruction 55

Whenever prefix of this instruction is present in any string instruction. Then it allows repeated execution of that instruction until the ZF becomes 0.

Control Transfer Instruction

This set consists of instructions like call, jump, loop and software interrupt instructions that basically controls the operation of the processor. These instructions do not modify the status of flag registers. Example:

instruction 61

This instruction transfers the control to the effective address within the segment stored in the register or memory location specified in the operand.

Processor Control Instruction

This set includes instructions for setting or clearing the carry, direction and interrupt flags inside the processor. example:

instruction 68

It is used to reset the carry flag to 0.


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