CPU Component & FDE Cycle

Question 1

what is a CPU ?

Answer 1

1. Central processing unit.
2. it has different components that allow it to carry out its tasks.
3. it execute instructions.

Question 2

what is the purpose of control unit?

Answer 2

1. it is used to control and coordinates the activates of the CPU
2. it is used to manage the flow of data between the CPU and other devices.
3. it is used to accept the next instruction
4. it decodes and executes the instruction
5. it stores back the resulting data in the main memory or in registers.

Question 3

what are buses?

Answer 3

1. busses are a set of parallel wires that are used to connect tow or more components insides of the CPU.
2. busses typically include 8,16,32 and 64 lines.
3. the width of the bus is the number of parallel wires it has.
4. the width of the bus is directly proportional to the number of bits it can transform.

Question 4

what is a control bus?

Answer 4

1. it is a bi - directional bus that is used to send control signals in both directions.
2. there are control lines that aim to reduce conflict between components and devices because the data and address busses are shared between them.
3. it provides status information between system components.

Question 5

what are the control signals?

Answer 5

1. Bus request : it is when a device or a components is requesting the CPU to use the data bus
2. Bus grant : it is when the CPU grant a device or a component to use the data bus.
3. Memory write : data on the data bus to be written to the addressed location.
4. Memory read : data from the address location to be put on the data bus.
5. Interrupt request : it is when a device is requesting to access the CPU.
6. Clock : it synchronise the CPU’s operations.

Question 6

what is the data bus ?

Answer 6

1. it is a bi directional bus that is used to transfer data in both directions.
2. it typically consist of 8,16,32 and 64 lines.
3. it transfers data and also instructions. ( this means that it does not only transfer data)

Question 7

what is an address bus ?

Answer 7

1. it is used to transmit memory addresses by specifying where data is to be sent or retrieved from.
2. the width of the address is proportional to the number of addressable location it can have.

Question 8

what is the ALU ?

Answer 8

1. Arithmetic and Logical Unit
2. it is used to carry out all the arithmetic and logical operations in the CPU.
3. arithmetic operations like:
   ADD
   SUBTRACT
   MULTIPLY
   DEVIDE
4. logical operations like:
   AND
   OR
   NOR
   XOR

Question 9

what are registers ?

Answer 9

1. small fast memory cells that is used to temporarily store data.
2. all arithmetic , logical and shift operations occur in registers.

Question 10

what are the names and functions of registers ?

Answer 10

1. PC is used to hold the address of the next instruction to be executed.
2. MAR is used to hold the address of the location in memory of the data that is to be read from or written to.
3. MDR is used to temporarily store the data that has been read or data that needs to be written.
4. CIR is used to hold the current instruction being executed, it is split into opcode and operand.
5. ACC is used to store the results from calculations.

Question 11

what is the FDE cycle ?

Answer 11

it is a sequence of operations that are used to execute an instruction.

Question 12

What are the phases of the FDE cycle ?

Answer 12

Fetch phase :
1. the address from the pc is copied to the MAR

2. the content of the PC is incremented by 1, so that it holds the address of the next instruction.
3. the data from that addressed location in memory is then transferred to the MDR by using the data bus.
4. the content of the MDR is then copied to the CIR

Decode phase :
5. the instruction is split into opcode and operand

Execute phase:
6. the instruction is then carried on the operand.

Question 13

what is an opcode ?

Answer 13

an opcode is used to determine the type of instruction and what hardware to use to execute it.

Question 14

what is an operand

Answer 14

an operand will hold either:

1. the address of the data that is to be used, which is then copied to the MAR.
2. the actual data to be operated on, which is then copied to the MDR.
3. the data that is to passed to the ALU/ACC