FDE cycle

Question 1

Fetch

Answer 1

-The address of the next instruction is held in the Program Counter (PC).

-This address is sent to Memory Address Register (MAR).

-The instruction at that address is fetched from main memory and sent to the Memory Data Register (MDR).

-The instruction is copied into the Current Instruction Register (CIR).

-The PC is incremented so it points to the next instruction.

Question 2

Decode

Answer 2

-The Control Unit (CU) decodes the instruction in the CIR.

-It identifies what action is needed (e.g. load data, perform an arithmetic operation, jump, etc.).

-The CU signals the necessary components (like the ALU or registers).

Question 3

Execute

Answer 3

-The instruction is carried out.

-This could involve:
-Data being read/written to memory.
-A calculation in the ALU.
-A change to the PC if it’s a jump/branch instruction.

-The cycle then repeats.