1.1.1 Structure and Function of the Processor Flashcards
(a) The Arithmetic and Logic Unit; ALU, Control Unit and Registers (Program Counter; PC, Accumulator; ACC, Memory Address Register; MAR, Memory Data Register; MDR, Current Instruction Register; CIR). Buses: data, address and control: how this relates to assembly language programs. (b) The Fetch-Decode-Execute Cycle; including its effects on registers. (c) The factors affecting the performance of the CPU: clock speed, number of cores, cache. (d) The use of pipelining in a processor to improve
What does the ALU do?
Performs all maths and logic operations
What does the CU do?
The control unit:
1. Sends signals to coordinate movement of data through the processor during the FDE cycle
2. Controls the buses
3. Decodes instructions
What are registers?
Temporary storage inside the CPU used for a specific purpose. Faster to access than RAM.
What are the registers in the CPU called?
ACC, PC, CIR, MAR, MDR
What does the ACC do?
The accumulator:
1. Acts as temporary storage for data being processed during calculations
2. Acts as a buffer for input and output operations in the processor
3. Is checked for conditional branching operations
What does the MAR do?
Stores the address of the next instruction or data to be accessed in memory
What does the MDR do?
Stores data and instructions which have been accessed from memory
What does the CIR do?
Holds data to be decoded into opcode and operand
What does the PC do?
Stores the address of the next instruction to be processed
What are the three buses?
Control bus, data bus, address bus
What does the control bus do?
Transmits control signals between the CU and other parts of the system
What does the data bus do?
Carries data between different system components
What does the address bus do?
Carries a memory address from the CU to memory
Six examples of control signals
(data) bus request, (data) bus grant, memory write, memory read, interrupt request, clock
What happens in the Fetch step of the FDE cycle
- Value in the PC is copied to the MAR
- Address in the MAR is sent down the address bus at the same time as a memory read signal is sent down the control bus
- The value in stored in the location specified by the address bus is sent to the MDR on the address bus
- The value in the MDR is copied to the CIR
- The value in the PC is incremented by one
What happens during the decode step of the FDE cycle?
The instruction in the CIR is split into opcode and operand.