Profile
Settings
Refer your friends
Sign out
The instructions provided to computers help the computer perform a task. The computers comprise instructions in groups called fields. Each field has different information and different significance based on which the CPU decides what to perform. The group of bits is used to perform a particular operation on the data. These operations are called instruction code or instruction format. The data on which operations are performed are stored in the computer. Different computers have their own set of instructions. The CPU or processor takes all these instructions from memory and decodes the bits to carry out the instructions.
The layout of bits of instruction is called an instruction format. The instruction format contains opcode (the instructions to be executed), operand (the data on which the instructions are to be executed), and addressing mode.
Format Of Instruction
The set of instructions that manages the operation codes is called the format of instruction. The design of bits in instruction is supported by the format of instruction. The length of instruction is generally preserved in multiples of character, which is 8bits. The instruction format determines the behaviour and complexity of instruction. Depending upon the number of addresses, the format of instruction is of variable length.
Types of instruction format include:
Zero(0) Address Instruction format
One(1) Address Instruction format
Two(2) Address Instruction format
Three(3) Address Instruction format
Types Of Instruction Format
Types of instruction formats are :
1. Zero(0) Address Instruction format
The instruction format in which there is no address field is called zero address instruction
In zero address instruction format, stacks are used
In zero order instruction format, there is no operand
2. One(1) Address Instruction format
The instruction format in which the instruction uses only one address field is called the one address instruction format
In this type of instruction format, one operand is in the accumulator and the other is in the memory location
It has only one operand
It has two special instructions LOAD and STORE
3. Two(2) Address Instruction format
The instruction format in which the instruction uses only two address fields is called the two address instruction format
This type of instruction format is the most commonly used instruction format
As in one address instruction format, the result is stored in the accumulator only, but in two addresses instruction format the result can be stored in different locations
This type of instruction format has two operands
It requires shorter assembly language instructions
4. Three(3) Address Instruction format
The instruction format in which the instruction uses the three address fields is called the three address instruction format
It has three operands
It requires shorter assembly language instructions
It requires more bits
Example Of format Of Instruction
1. Zero Address Instruction examples
Assembly language instruction – PUSH A, PUSH B etc.
Stack transfer operation – TOS <- A, TOS <- B etc.
2. One Address Instruction examples
Assembly language instruction – LOAD C, ADD B, STORE T etc.
Operation Register instruction – AC <- M[T], AC <- M[C] etc.
3. Two Address Instruction examples
Assembly language instruction – MOV R1, A; ADD R1, B etc.
Operation Register instruction – R1 <- M[A], R2 <- M[C] etc.
Three Address Instruction examples
Assembly language instruction – ADD R1, A, B etc.
Operation Register instruction – R1 <- M[A] + M[B] etc.
Parts Of Instruction Format
The parts of the instruction format are:
1. Addressing Mode
The data is represented in the instruction format with the help of addressing mode
The addressing mode is the first part of the instruction format
The data can either be stored in the memory of a computer or it can be located in the register of the CPU
2. Operation Code( OPCODE)
The operation code gives instructions to the processor to perform the specific Operation
The operation code is the second part of the instruction format
3. OPERAND
It is the part of the instruction format that specifies the data or the address of the data
Depending upon the processor of the computer the instruction format contains zero to three operands
Conclusion
A standard machine which can be directly decoded and executed by the CPU is called instruction format. It is a sequence of bits in a machine instruction that defines the layout of the instruction. The format of instruction provides specific information to the CPU regarding the information to be performed. The parts of the format of instruction are addressing mode, operation code and operand. The characteristic of a good format of instruction is that all the components of instruction should be present. The group of Instructions is called the instruction set.
Also check:
