Fetch Execute Cycle Flashcards
What is a bus?
A bus is a set of parallel wires connecting two or more independent components of a computer system in order to pass signals between them.
What are the three buses?
Data
Address
Control
What does the data bus do?
Carries Data/instructions from the Main memory to the Processor (or from other secondary storage devices) to the processor (Bi-Directional)
Data can be read/written
What does the address bus do?
Carries Addresses from the processor to main memory other I/O devices
It is one direction
The processor generates an address
All data/instructions are returned to the Data Bus
What does the control bus do?
Controls Signals are sent along the control bus:
E.g Memory Read/write
The instructions which was data will be travelling to/from memory
Where are the contents of the program counter put?
Into the MAR (Memory Address Register)
The program counter is incremented for every what?
Each instruction of the program being executed
Where are the addresses transferred?
Along the address bus to the main memory
Where is the data/institution that has been addressed transferred to?
To the processor along the data bus, and then held in the MAR
What happens after the instruction is put in the MAR?
The instruction is transferred to the Current Instruction Register
What happens in the fetch part of the fetch execute cycle?
Address from the Program Counter is copied to the MAR
Instructions from the MAR is fetched and copied to the MDR
The Instruction in the MDR s copied to the CDR
Increment the Program Counter
What happens in the Decode part of the fetch execute cycle?
The instruction in the CIR is decoded by the control unit
Data may be loaded into the MDR
What happens in the execute part of the fetch execute cycle?
The instruction is executed
The ALU may be used for logic or calculations
The result is stored in the accumulator
