Processors And The FDE Cycle

Question 1

What does the Arithmetic Logical Unit (ALU) do?

Answer 1

Performs all arithmetic and logical operations on data during the execution of an instruction

Question 2

What does the Control Unit (CU) do?

Answer 2

Coordinates activities in the CPU memory and peripherals

Question 3

What does the clock do?

Answer 3

Continuous sequence of clock pulses to step the control unit through its operations

Question 4

What do registers do?

Answer 4

Chip memory for temporary storage of binary values

Question 5

What does the Program Counter (PC) do?

Answer 5

Holds the address of the next instruction to be executed

Question 6

What does the Current Instruction Register (CIR) do?

Answer 6

Stores the current instruction being run

Question 7

What are general purpose registers

Answer 7

Can store binary numbers

Question 8

What does the Memory Address Register (MAR) do?

Answer 8

Holds the address of a memory location from which data will be read or data will be written to

Question 9

What does the memory buffer register (MBR) do?

Answer 9

Temporarily stores data read or written to memory

Question 10

What does the status register (SR) do?

Answer 10

Contains many bits that are set (1) or cleared (0) depending on the result of an instruction

Question 11

What are the steps in the Fetch part of the FDE cycle

Answer 11

1 - The processor gets the memory address of the current instruction from the PC
2 - Passes the address to the MAR and sends it along the address bus
3 - The contents of the PC is incremented to point to the next instruction to be executed
4 - The control unit instructs a memory read operation to allow the contents of the memory location to be transferred and passes the data back along the data bus to the MDR
5 - The contents of the MDR are copied to the CIR

Question 12

What are the steps of the decode part of the FDE cycle

Answer 12

The data in the MDR is passed to the CU which then decodes the instruction and then signals to the other components the instruction is to be completed

Question 13

What are the steps of the Execute part of the FDE cycle

Answer 13

1 - The instruction is executed, using the ALU
2 - The SR may also be updated at this stage

Question 14

What is an interrupt (FDE)

Answer 14

A signal sent to the processor from a program or an external device, it immediately halts all other processes until it is completed

Question 15

Give an example of an interrupt (FDE)

Answer 15

Power low
Fault in hardware
Alarm