CPU Component & FDE Cycle Flashcards
1
Q
what is a CPU ?
A
- Central processing unit.
- it has different components that allow it to carry out its tasks.
- it execute instructions.
2
Q
what is the purpose of control unit?
A
- it is used to control and coordinates the activates of the CPU
- it is used to manage the flow of data between the CPU and other devices.
- it is used to accept the next instruction
- it decodes and executes the instruction
- it stores back the resulting data in the main memory or in registers.
3
Q
what are buses?
A
- busses are a set of parallel wires that are used to connect tow or more components insides of the CPU.
- busses typically include 8,16,32 and 64 lines.
- the width of the bus is the number of parallel wires it has.
- the width of the bus is directly proportional to the number of bits it can transform.
4
Q
what is a control bus?
A
- it is a bi - directional bus that is used to send control signals in both directions.
- there are control lines that aim to reduce conflict between components and devices because the data and address busses are shared between them.
- it provides status information between system components.
5
Q
what are the control signals?
A
- Bus request : it is when a device or a components is requesting the CPU to use the data bus
- Bus grant : it is when the CPU grant a device or a component to use the data bus.
- Memory write : data on the data bus to be written to the addressed location.
- Memory read : data from the address location to be put on the data bus.
- Interrupt request : it is when a device is requesting to access the CPU.
- Clock : it synchronise the CPU’s operations.
6
Q
what is the data bus ?
A
- it is a bi directional bus that is used to transfer data in both directions.
- it typically consist of 8,16,32 and 64 lines.
- it transfers data and also instructions. ( this means that it does not only transfer data)
7
Q
what is an address bus ?
A
- it is used to transmit memory addresses by specifying where data is to be sent or retrieved from.
- the width of the address is proportional to the number of addressable location it can have.
8
Q
what is the ALU ?
A
- Arithmetic and Logical Unit
- it is used to carry out all the arithmetic and logical operations in the CPU.
- arithmetic operations like:
ADD
SUBTRACT
MULTIPLY
DEVIDE - logical operations like:
AND
OR
NOR
XOR
9
Q
what are registers ?
A
- small fast memory cells that is used to temporarily store data.
- all arithmetic , logical and shift operations occur in registers.
10
Q
what are the names and functions of registers ?
A
- PC is used to hold the address of the next instruction to be executed.
- MAR is used to hold the address of the location in memory of the data that is to be read from or written to.
- MDR is used to temporarily store the data that has been read or data that needs to be written.
- CIR is used to hold the current instruction being executed, it is split into opcode and operand.
- ACC is used to store the results from calculations.
11
Q
what is the FDE cycle ?
A
it is a sequence of operations that are used to execute an instruction.
12
Q
What are the phases of the FDE cycle ?
A
Fetch phase :
1. the address from the pc is copied to the MAR
- the content of the PC is incremented by 1, so that it holds the address of the next instruction.
- the data from that addressed location in memory is then transferred to the MDR by using the data bus.
- 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.
13
Q
what is an opcode ?
A
an opcode is used to determine the type of instruction and what hardware to use to execute it.
14
Q
what is an operand
A
an operand will hold either:
- the address of the data that is to be used, which is then copied to the MAR.
- the actual data to be operated on, which is then copied to the MDR.
- the data that is to passed to the ALU/ACC
