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ECT 358 PowerPoint Presentation

ECT 358

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ECT 358

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  1. ECT 358 Lecture 18 Memory

  2. Blessed is he who, having nothing to say, refrains from giving wordy evidence of the fact. The tongue of the wise useth knowledge aright: but the mouth of fools poureth out foolishness. Proverbs 15:2

  3. Memory Types • Read Only Memory (ROM) • Programmable Read Only Memory (PROM) • Erasable PROM (EPROM) • Electrically Erasable PROM (EEPROM) • FLASH • Random Access Memory (RAM) • Static RAM (SRAM) • Ferroelectric Nonvolatile Memory

  4. Read Only Memory (ROM) • Memory remains unchanged during operation and after power is removed • Structurally modified for program • Address and Data lines • Address Decoder • Bipolar/CMOS/nMOS/pMOS

  5. Read Only Memory (ROM)

  6. Programmable ROM (PROM) • Similar structure to ROM • One time programmable • PROM burner • Bipolar technology • Can be modified slightly (unburnt fuses)

  7. Programmable ROM (PROM)

  8. Erasable PROM (EPROM) • Similar to PROM • Floating nMOS transistor gate • Additional gate • High programming voltage • UV erasable • Bulk erase • 20 minute erase time

  9. Erasable PROM (EPROM)

  10. Electrically Erasable PROM (EEPROM) • Similar to EPROM • Electrically erased vice UV erased • Electrical pulses break down gate • High negative charge (-15 volts) • Programmed in circuit with low voltage • Individual words erased • 100-100000 erase cycles • Much faster than UV for erasing

  11. Electrically Erasable PROM (EEPROM)

  12. FLASH • Similar to EEPROM’s • Additional circuitry to selectively erase and program the device in circuit • Lower power consumption • Simultaneous erasing of blocks • Multiple bits per cell (1-3 levels) • 100000 erase cycles

  13. FLASH

  14. Random Access Memory (RAM) • Contents changed during operation • Data lost when power is removed • RAM circuit is fixed, not programmed • RAM contents are programmed • Requires refresh

  15. Static RAM (SRAM) • Transistor-Capacitor storage cell structure that does not require refresh • Fast Cache • 6 transistor circuit • Wide input decoder • Rectangular versus square physical layout

  16. Ferroelectric Nonvolatile Memory • Hysteresis effect • Electrical polarization under applied voltage • Hard Drives • Magnetic Tape • Floppy Drives • Drum Drives • Bi-stable states