ECT 358ECT 358

Lecture 18Lecture 18

MemoryMemory

Blessed is he who, having Blessed is he who, having nothing to say, refrains nothing to say, refrains

from giving wordy from giving wordy evidence of the fact.evidence of the fact.

The tongue of the wise useth The tongue of the wise useth knowledge aright: but the mouth of knowledge aright: but the mouth of

fools poureth out foolishness.fools poureth out foolishness.

Proverbs 15:2Proverbs 15:2

Memory TypesMemory Types• Read Only Memory (ROM)Read Only Memory (ROM)

• Programmable Read Only Memory Programmable Read Only Memory (PROM)(PROM)

• Erasable PROM (EPROM)Erasable PROM (EPROM)

• Electrically Erasable PROM (EEPROM)Electrically Erasable PROM (EEPROM)

• FLASHFLASH

• Random Access Memory (RAM)Random Access Memory (RAM)

• Static RAM (SRAM)Static RAM (SRAM)

• Ferroelectric Nonvolatile MemoryFerroelectric Nonvolatile Memory

Read Only Memory (ROM)Read Only Memory (ROM)

• Memory remains unchanged during Memory remains unchanged during operation and after power is removedoperation and after power is removed

• Structurally modified for programStructurally modified for program

• Address and Data linesAddress and Data lines

• Address DecoderAddress Decoder

• Bipolar/CMOS/nMOS/pMOSBipolar/CMOS/nMOS/pMOS

Read Only Memory (ROM)Read Only Memory (ROM)

Programmable ROM (PROM)Programmable ROM (PROM)

• Similar structure to ROMSimilar structure to ROM

• One time programmableOne time programmable

• PROM burnerPROM burner

• Bipolar technologyBipolar technology

• Can be modified slightly (unburnt fuses)Can be modified slightly (unburnt fuses)

Programmable ROM (PROM)Programmable ROM (PROM)

Erasable PROM (EPROM)Erasable PROM (EPROM)

• Similar to PROMSimilar to PROM

• Floating nMOS transistor gateFloating nMOS transistor gate

• Additional gateAdditional gate

• High programming voltageHigh programming voltage

• UV erasableUV erasable

• Bulk eraseBulk erase

• 20 minute erase time20 minute erase time

Erasable PROM (EPROM)Erasable PROM (EPROM)

Electrically Erasable PROM Electrically Erasable PROM (EEPROM)(EEPROM)

• Similar to EPROMSimilar to EPROM

• Electrically erased vice UV erasedElectrically erased vice UV erased

• Electrical pulses break down gateElectrical pulses break down gate

• High negative charge (-15 volts)High negative charge (-15 volts)

• Programmed in circuit with low voltageProgrammed in circuit with low voltage

• Individual words erasedIndividual words erased

• 100-100000 erase cycles100-100000 erase cycles

• Much faster than UV for erasingMuch faster than UV for erasing

Electrically Erasable PROM Electrically Erasable PROM (EEPROM)(EEPROM)

FLASHFLASH

• Similar to EEPROM’sSimilar to EEPROM’s

• Additional circuitry to selectively erase Additional circuitry to selectively erase and program the device in circuitand program the device in circuit

• Lower power consumptionLower power consumption

• Simultaneous erasing of blocksSimultaneous erasing of blocks

• Multiple bits per cell (1-3 levels)Multiple bits per cell (1-3 levels)

• 100000 erase cycles100000 erase cycles

FLASHFLASH

Random Access Memory Random Access Memory (RAM)(RAM)

• Contents changed during operationContents changed during operation

• Data lost when power is removedData lost when power is removed

• RAM circuit is fixed, not programmedRAM circuit is fixed, not programmed

• RAM contents are programmedRAM contents are programmed

• Requires refreshRequires refresh

Static RAM (SRAM)Static RAM (SRAM)

• Transistor-Capacitor storage cell Transistor-Capacitor storage cell structure that does not require refreshstructure that does not require refresh

• Fast CacheFast Cache

• 6 transistor circuit6 transistor circuit

• Wide input decoderWide input decoder

• Rectangular versus square physical Rectangular versus square physical layoutlayout

Ferroelectric Nonvolatile Ferroelectric Nonvolatile MemoryMemory

• Hysteresis effectHysteresis effect

• Electrical polarization under applied Electrical polarization under applied voltagevoltage

• Hard DrivesHard Drives

• Magnetic TapeMagnetic Tape

• Floppy DrivesFloppy Drives

• Drum DrivesDrum Drives

• Bi-stable statesBi-stable states