Memory Data Transfers

Memory Reads

For data to be read from memory the sequence is as follows:

  1. Processor signals the memory location to be read by placing the memory address onto the address bus.
  2. Specific memory chips that hold the memory location are made ready and selected.
  3. A delay is added to allow the memory to settle and be available to read.
  4. Data is placed onto the data bus.
  5. Control unit of the processor turns on the read line of the control bus.
  6. Data is placed into the MDR.

Step 2 is necessary as computer memory consists of more than one chip. To read from memory the correct chip must be chosen. Step 3 introduces the time necessary for all electronic components to respond to supplied signals.

Memory Writes

For data to be written to memory the sequence is as follows:

  1. Processor signals the memory location to be written by placing the memory address onto the address bus.
  2. Processor places the data to be written onto the data bus.
  3. Specific memory chips that hold the memory location are made ready and selected.
  4. A delay is added to allow the memory to settle and be available to write.
  5. Control unit of the processor turns on the write line of the control bus.
  6. Data is written to the correct memory location.

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