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Datapath operation and instruction cycles

Short answer

The datapath uses ALU, registers, and buses to execute operations: operands fetched, ALU selected, result stored. The instruction cycle consists of fetch, decode, operand fetch, execute, and store result, repeating for each instruction. Status flags inform the controller for conditional actions.

Explain the data path operation and its instruction cycles.

The datapath of a processor contains the registers, ALU and buses that carry out computation under the control unit's signals. Its operation is organised into the instruction cycle.

Datapath operation

Operands come from registers (or memory) onto the ALU inputs, the ALU executes the selected function (add, subtract, AND, shift, compare), and the result goes back to a register or memory. Status flags (zero, carry, sign) go to the controller.

 Register file --> [ALU] --> Result bus --> Register file
        ^            ^ function select
        |            |
   ----- control signals from controller -----

Instruction cycles (steps)

  1. Fetch: the datapath sends PC to memory, IR <- instruction, PC <- PC + 1.
  2. Decode: opcode decoded by the controller; registers/operand addresses chosen.
  3. Fetch operands: read registers or memory into ALU input registers.
  4. Execute: the ALU operates (or the address/branch is computed).
  5. Store result: write result to register or memory.

Example: ADD R1, R2, R3: fetch the instruction, decode, read R2 and R3, the ALU adds, then R1 <- sum. The cycle then repeats for the next instruction.

✓ Answer checked by Claude Opus 5.5 (high effort)

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