Fetch, decode, execute

Fetch

• The PC is copied to MAR
• The fetch signal is sent across the control bus, the contents of MAR acrross address bus
• The contents of the memory location stored in the MAR are then sent across the data bus and stored in CIR
• The PC is incremented by one

Decode

• The Contents of the CIR are sent to control unit
• The control unit then decodes the instruction

Execute

• The registers can be changed in differnt ways during execution.
• E.g If it is a calculation, then the contents of the MDR and ACC are sent to the ALU and then the results are sent back to the ACC