FDE Cycle

• What is the FDE cycle ?

  The process cpu uses to FDE an instruction them in a repetitive cycle.
• What does a Computer do ?

  • Takes an input, processes data, and delivers output
• Computer program


  A set of instructions that a computer follows to carry out its function
• Components of a computer

  • Memory that stores the program
  • CPU (processor) that carries out the instruction
• Fetch stage


  1. The program counter is checked to get the address of the next instruction

  2. The address is copied into the memory address register

  3. The address is sent along the address bus to main memory

  4. The control unit sends a read signal along the control bus to main memory

  5. The content stored in the memory address is sent along the data bus to the memory data register

  6. The data in the memory data register is copied into the current instruction register
• Decode stage


  The instruction in the CIR is decoded to determine the operation (opcode) and the operand
• Execute stage


  1. The address specified by the operand is sent to the memory address register

  2. The control unit sends a read signal along the control bus to main memory

  3. The content stored at the memory address is sent along the data bus to the memory data register

  4. The contents of the memory data register are copied to the accumulator
• The program counter is added after each instruction is fetched
• Branching


  When a program doesn't necessarily follow strictly in sequence, but may jump around based on certain conditions
• Branching process


  1. The program counter is updated with the contents of the operand in the current instruction register, instead of simply being incremented

  2. This allows the program to jump to a different memory location
• Computers perform billions of fetch-decode-execute cycles per second