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Chapter 8

Chapter 8. Memory Basics. 8-1 Memory definitions. Memory is a collection of cells capable of storing binary information. Two types of memory: Random-Access Memory (RAM) Read-Only Memory (ROM). 8-2 Random-Access Memory.

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Chapter 8

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  1. Chapter 8 Memory Basics

  2. 8-1 Memory definitions • Memory is a collection of cells capable of storing binary information. • Two types of memory: • Random-Access Memory (RAM) • Read-Only Memory (ROM)

  3. 8-2 Random-Access Memory • Memory cell can be accessed to transfer information to or from any desired location • Access will take the same time regardless of the location • compare to serial memory such as hard drive, tape etc.

  4. Block diagram of memory

  5. Example of memory content

  6. Write and Read Operation • Write • Apply the address on address lines (bus) • Apply data on data lines (bus) • Activate the Write input • Read • Apply the address on address lines (bus) • Activate the Read input

  7. Timing waveforms Operation of memory is controlled by an external device, such as CPU Memory doesn’t employ CPU clock Operations are timed by changes in values on control input Access time for read: max. time from application of address to appearance of data on Data Output Write cycle time: max. time form application of address to completion of all operation required to store a word

  8. Timing waveforms 4 clocks is needed for both Write cycle and Access time

  9. Properties of memory • Volatile: data disappeared after turning off the power • Static RAM (SRAM): faster, less capacity • Dynamic RAM (DRAM): slower, need refresh, more capacity • Non-volatile: date kept after turning off the power • Magnetic disk

  10. 8-3 SRAM Integrated Circuits Static RAM cell

  11. RAM bit slice model

  12. 16-word by one-bit RAM chip

  13. Coincident selection (16x1 RAM using 4x4 cell array)

  14. Coincident selection (8x2 RAM using 4x4 cell array)

  15. 8-4 Array of SRAM ICs • Symbol for 64K x 8 RAM

  16. Block diagram of a 256K x 8 RAM • Extension from 64K x 8 RAM • Fig. 8-10

  17. Block diagram of a 64K x 16 RAM

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