2.1.2 Instruction Execution Cycle

  • An Execution Cycle often requires more than one clock cycle to complete and has multiple steps to complete execution
    1. Fetch Instruction: Fetch instruction from the instruction queue
    2. Decode: Look at binary instruction and decode based upon args and opcode
    3. Execute: Executes the instruction and updates any flag bits
    4. Store Result: Store result in cache or main memory
Basic CPU block diagram
  • A more detailed description of this now follows
    1. Address of instruction placed on address bus
    2. Instruction fetched from memory and put on data bus and code is now available in code  cache
    3. Instruction pointer determines which instruction to execute next (PC)
    4. Instruction decoder decodes and tells the control unit what type of instruction this is
    5. Control unit performs the operations needed to compute something reading data as it needs and writing when complete

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