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All About the Central Processing Unit

John Welsh

on 27 February 2012

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Transcript of CPU

Central Processing Unit Role Components Role... As the human brain processes
all human interaction with the world
The CPU processes interaction with
user and attached peripherals The CPU then, is the core component
of the system, and the most expensive. Data Transfers Timing Logical operations Executing instructions Decodes Instructions Coordinates Components RAM BUI MDR MAR PC Control
Unit ALU ACC IR Bus Interface Unit Internal to CPU
Allows CPU to interface with System Buses
It facilitates the transfer of data to and from the CPU Control Unit Oversees the fetch execute process
Sends appropriate signals
Initialises components
Maintains timing Connected to the Address Bus
Used to store memory addresses when the CPU access RAM to read or write
The approraite address is stored in the MAR Memory Address Register Memory Data Register Directly Connected to the Data Bus
Instructions or data is taken from the Data Bus and stored here Instruction Register Instructions read into the CPU to the MDR are passed to the IR to be decoded and processed Accumulator General Purpose Register
Stores values prior to and resulting from arithmetical operations
Works in conjuction with the ALU - Next... Performs arithmetic and logical functions
That is: Add, subtract, AND, NOR, NOT XOR ...
Notice the "V" shape - in one end, out the other Arithmetic Logic Unit Holds the address of the next instruction to be fetched
Reflects the flow of program code as the program runs
It does so by incrementing by 1 to access contiguously stored data from memory Program Counter Fetch Execute Cycle... 1. Address for next instruction is read from PC to MAR 2. Control U places the MEM address onto Address Bus 3. CU sets MEMR to low telling RAM to place data onto bus 4.. Data read to MDR. MEMR remains low if more data is required 5. PC is incremented by 1 in preparation for reading more instructions 6. All bytes read in, data is passed to IR - subsequent decoding and execution 7. After decoding, data passed to ACC if logical/arithmetical function required 8. ACC passed data to ALU. Its then processed and returned to ACC 9. Process repeats until PC indicates that all instructions have been processed JW Designed by... Reid Kerr College BIU MAR Control
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