Topic One

Topic One

1. Fetch-Decode-Execute

   • Fetch
     • The PC hold the instruction of the next instruction
     • The address is copied into the MAR
     • The address is then sent along the address bus, where it waits to receive a signal on the control bus
     • The CU sends signal on the control bus to the memory controller to memory read
     • The contents in the address can be transferred along the data bus
     • The value from the RAM now goes to the CIR
     • The instruction has now been fetched so we can now increase the PC to get the next instruction.
   • Decode
     • The instruction in the CIR is now divided into binary code standing for the operation to be carried out
     • The Control Unit interrupts the operation code so that the processor knows what to do next
   • Execute
     • The address is sent to the MAR The address is sent to the MAR
     • The address is sent down the data bus where the MDR has the data the was in RAM to be passed to the ACC.
     • The ACC then receives the value and ready to fetch the next instruction .