The CPU

  • Basic Operation.
  • There are a number of ways we need to control registers and other things, and we want to number them.
    1. ACC -> Bus
    2. load ACC
    3. PC-> Bus
    4. load PC
    5. load IR
    6. load MAR
    7. MDR -> BUS
    8. load MDR
    9. ALU -> ACC
    10. ADD -> PC
    11. ALU operation
    12. ALU operation
    13. Addr -> Bus
    14. CS
    15. Read/not Write
  • Why does the ALU get two numbers?
  • We have already mentioned the fetch/execute loop, but now we can make it much more concrete now.
  • Notice the numbers beside each box. This is called the state.
  • For every instruction, we go through states 0-3
  • For a store we use states 4 and 5
  • For a load, we use state 6 and 7
  • For an add, we use state 6 and 8
  • What do we need to do at state 0?
  • What does each control line do?
  • How long does the state need to last last?
  • Now consider the Control portion of our machine.