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Fetch-Execute cycle

Fetch-Execute cycle. Memory Read operation. Read from memory. PC. Main Memory. 1. MAR. Address bus. Other registers. Data bus. MDR. Control bus. ALU. Control Unit. Clock pulses. The Program Counter (PC) holds the address of the next instruction. Electronic Clock. PC. Main

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Fetch-Execute cycle

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  1. Fetch-Execute cycle

  2. Memory Read operation Read from memory

  3. PC Main Memory 1 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit Clock pulses The Program Counter (PC) holds the address of the next instruction Electronic Clock

  4. PC Main Memory 10110111 1 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit Clock pulses The contents of the PC are copied to the Memory Address Register (MAR) Electronic Clock

  5. PC Main Memory 1 MAR Address bus Other registers 10110111 Data bus MDR Control bus ALU Control Unit Clock pulses Memory address to be accessed is placed onto the address bus Electronic Clock

  6. PC Main Memory 1 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit >>read>> Clock pulses Electronic Clock The control bus sends a read signal

  7. PC Main Memory 01010111 1 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit The contents of the memory location are passed along the data bus to the Memory Data Register (MDR) Clock pulses Electronic Clock

  8. PC Main Memory 2 1 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit Clock pulses The PC is incremented ready for the next instruction Electronic Clock

  9. Memory Write operation Write to memory

  10. PC Main Memory 2 MAR Address bus Other registers Data bus MDR 1110011 Control bus ALU Control Unit Clock pulses Electronic Clock Data is placed onto the data bus

  11. PC Main Memory 2 MAR Address bus Other registers 11110010 Data bus MDR Control bus ALU Control Unit Clock pulses Memory address to be written to is placed onto the address bus Electronic Clock

  12. PC Main Memory 2 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit >>write>> Clock pulses Electronic Clock A ‘write’ signal is sent along the control bus

  13. PC Main Memory 2 MAR Address bus Other registers Data bus MDR 10111110 Control bus ALU Control Unit Clock pulses Electronic Clock The data is transferred to the destination in memory

  14. PC Main Memory 3 2 MAR Address bus Other registers Data bus MDR Control bus ALU Control Unit Clock pulses Electronic Clock The PC is incremented

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