Define instruction cycle and divide instruction cycle into sub cycles with the help of diagram, explain the sequence in which sub cycles are executed.OR Explain the different cycles of an instruction execution.OR Explain all the phases of instruction cycle.

Instruction Cycle Overview:

The instruction cycle is the process by which a computer retrieves a program instruction from memory, interprets it, and executes the necessary actions. It consists of three main phases: Fetch, Decode, and Execute.

Subcycles of the Instruction Cycle:

1. Fetch Cycle:

• Purpose: Retrieve the next instruction from memory.
• Steps:
  1. Program Counter (PC) Placement: The address of the next instruction (opcode) is placed on the address bus by the program counter.
  2. Memory Access: CPU sends control signals to memory to read the opcode.
  3. Data Transfer: Opcode is transferred from memory to CPU via the data bus.

2. Decode Cycle:

• Purpose: Interpret the opcode fetched from memory.
• Steps:
  1. Transfer to Data Register (DR): Opcode is placed in the Data Register.
  2. Transfer to Instruction Register (IR): Opcode moves to the Instruction Register.
  3. Decoding: CPU’s decoder circuitry interprets the opcode to determine the operation to be performed.

3. Execute Cycle:

• Purpose: Perform the operation specified by the instruction.
• Steps:
  1. Perform Operation: If the instruction involves arithmetic or logic, the Arithmetic Logic Unit (ALU) is used to execute the operation.
  2. Update Registers: Any necessary updates to CPU registers or memory locations are performed.

Sequence of Subcycles Execution:

1. Fetch Cycle: The CPU retrieves the opcode from memory using the address provided by the program counter.
2. Decode Cycle: Once the opcode is fetched, it’s transferred to the Instruction Register and decoded by the CPU’s decoder circuitry to determine the operation.
3. Execute Cycle: With the opcode decoded, the CPU performs the operation specified by the instruction, utilizing the ALU if necessary, and updates any relevant registers.

Conclusion:

The instruction cycle is crucial for the functioning of a computer, as it allows the CPU to fetch, interpret, and execute instructions stored in memory. By breaking down the cycle into these sub cycles, the CPU can efficiently process instructions and perform the required tasks.