computer science

  • Created by: megan :D
  • Created on: 10-09-22 22:53

Embedded Computers

  • a small device that contaibs all components of a computer
  • e.g. microwave, washing machine, satnav, camera

pros of embedded system - 

  • physically small
  • less power - cheaper to run
  • less power - no overheating
  • efficient
  • easy to replace - built on single printed circuit
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Data Buses

Data Bus - carries binary data around computer

Address Bus - carries address of memory locations used to store data

Control Bus - sends and recieves signals that controls components + CPU

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  • fetches memory from RAM
  • fetch-execute-decide cycle
  • purpose is to process data
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Parts of CPU

The Control Unit - 

  • controls the way data moves around the CPU
  • Controls + monitors flow of data between CPU and input / output devices
  • Executes instructions provided by program

The Arithmetic Logic Unit ( ALU ) -

  • performs arithmetic operations
  • logic operations / comparisons
  • shift operations

Registers - 

  • type of memory
  • temporarily holds data while software is running
  • faster than RAM and Cache
  • inside CPU
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Von Neumann Architecture - card one

  • both data and software being used are stored in RAM
  • task can be changed by loading different program into memory

Features of Von Neumann Layout - 

  • RAM has enough memory for both data and program ds - easy to load different program
  • control unit handles movement of data and instructions
  • info and instructions carried by buses
  • ALU in charge of Arithmetic and Logic Operations
  • way of inputting and outputting data
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Registers - part one

Memory Address Register ( MAR ) -

  • every instruction is in a specific location
  • each location has a unique address
  • address being accessed is temporarily stored in MAR
  • address passed to RAM via Address Bus

Memory Data Register ( MDR ) -

  • data must be stored in MDR for it to be fetched from RAM
  • data can travel both ways ( unlike instructions )
  • can be fetched from RAM to be decoded by CPU
  • after processing it can be sent back to RAM to be temporarily stored
  • all data must pass through the MDR via data bus
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Registers - part two

Program Counter ( PC ) -

  • points to instruction currently being executed
  • as each instruction is processed, PC is updated with address of next instuction to fetch
  • PC copies info to MAR and increments

Accumulator -

  • Temporarily stores ALU's results
  • makes it simpler to write software that handles data
  • program runs faster - registers are faster than RAM

Current Instruction Register ( CIR ) -

  • holds the instruction that is currently being decoded and executed
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Fetch-Execute-Decode Cycle

step 1 -   address in PC ( 305 ) is copied to MAR

step 2 -   address in MAR is passed onto Address Bus and Control Unit sends a signal to RAM                 to read this address

step 3 -   instruction at 305 is sent across Data Bus and copied into MDR, then the MDR is                      copied into the Instruction Register. The PC is then incremented

step 4 -   instruction's decoded by Control Unit, so CPU knows what to do.Various parts of the                  CPU are prepared for the next stage

step 5 -   the decoded instructions performed. and the PC is already pointing to the next                            intstruction

step 6 -   cycle restarts

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