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ECT 358 Lecture 18 Memory


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ECT 358 Lecture 18 Memory

  1. 1. ECT 358 Lecture 18 Memory
  2. 2. <ul><li>Blessed is he who, having nothing to say, refrains from giving wordy evidence of the fact. </li></ul><ul><li>The tongue of the wise useth knowledge aright: but the mouth of fools poureth out foolishness. </li></ul><ul><li>Proverbs 15:2 </li></ul>
  3. 3. Memory Types <ul><li>Read Only Memory (ROM) </li></ul><ul><li>Programmable Read Only Memory (PROM) </li></ul><ul><li>Erasable PROM (EPROM) </li></ul><ul><li>Electrically Erasable PROM (EEPROM) </li></ul><ul><li>FLASH </li></ul><ul><li>Random Access Memory (RAM) </li></ul><ul><li>Static RAM (SRAM) </li></ul><ul><li>Ferroelectric Nonvolatile Memory </li></ul>
  4. 4. Read Only Memory (ROM) <ul><li>Memory remains unchanged during operation and after power is removed </li></ul><ul><li>Structurally modified for program </li></ul><ul><li>Address and Data lines </li></ul><ul><li>Address Decoder </li></ul><ul><li>Bipolar/CMOS/nMOS/pMOS </li></ul>
  5. 5. Read Only Memory (ROM)
  6. 6. Programmable ROM (PROM) <ul><li>Similar structure to ROM </li></ul><ul><li>One time programmable </li></ul><ul><li>PROM burner </li></ul><ul><li>Bipolar technology </li></ul><ul><li>Can be modified slightly (unburnt fuses) </li></ul>
  7. 7. Programmable ROM (PROM)
  8. 8. Erasable PROM (EPROM) <ul><li>Similar to PROM </li></ul><ul><li>Floating nMOS transistor gate </li></ul><ul><li>Additional gate </li></ul><ul><li>High programming voltage </li></ul><ul><li>UV erasable </li></ul><ul><li>Bulk erase </li></ul><ul><li>20 minute erase time </li></ul>
  9. 9. Erasable PROM (EPROM)
  10. 10. Electrically Erasable PROM (EEPROM) <ul><li>Similar to EPROM </li></ul><ul><li>Electrically erased vice UV erased </li></ul><ul><li>Electrical pulses break down gate </li></ul><ul><li>High negative charge (-15 volts) </li></ul><ul><li>Programmed in circuit with low voltage </li></ul><ul><li>Individual words erased </li></ul><ul><li>100-100000 erase cycles </li></ul><ul><li>Much faster than UV for erasing </li></ul>
  11. 11. Electrically Erasable PROM (EEPROM)
  12. 12. FLASH <ul><li>Similar to EEPROM’s </li></ul><ul><li>Additional circuitry to selectively erase and program the device in circuit </li></ul><ul><li>Lower power consumption </li></ul><ul><li>Simultaneous erasing of blocks </li></ul><ul><li>Multiple bits per cell (1-3 levels) </li></ul><ul><li>100000 erase cycles </li></ul>
  13. 13. FLASH
  14. 14. Random Access Memory (RAM) <ul><li>Contents changed during operation </li></ul><ul><li>Data lost when power is removed </li></ul><ul><li>RAM circuit is fixed, not programmed </li></ul><ul><li>RAM contents are programmed </li></ul><ul><li>Requires refresh </li></ul>
  15. 15. Static RAM (SRAM) <ul><li>Transistor-Capacitor storage cell structure that does not require refresh </li></ul><ul><li>Fast Cache </li></ul><ul><li>6 transistor circuit </li></ul><ul><li>Wide input decoder </li></ul><ul><li>Rectangular versus square physical layout </li></ul>
  16. 16. Ferroelectric Nonvolatile Memory <ul><li>Hysteresis effect </li></ul><ul><li>Electrical polarization under applied voltage </li></ul><ul><li>Hard Drives </li></ul><ul><li>Magnetic Tape </li></ul><ul><li>Floppy Drives </li></ul><ul><li>Drum Drives </li></ul><ul><li>Bi-stable states </li></ul>