EEPROM

EEPROM

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EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...

 used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration tables or device configuration.

When larger amounts of static data are to be stored (such as in USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...

s) a specific type of EEPROM such as flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

 is more economical than traditional EEPROM devices. EEPROMs are realized as arrays of floating-gate transistors.

EEPROM is user-modifiable read-only memory (ROM) that can be erased and reprogrammed (written to) repeatedly through the application of higher than normal electrical voltage generated externally or internally in the case of modern EEPROMs. EPROM usually must be removed from the device for erasing and programming, whereas EEPROMs can be programmed and erased in circuit. Originally, EEPROMs were limited to single byte operations which made them slower, but modern EEPROMs allow multi-byte page operations. It also has a limited life - that is, the number of times it could be reprogrammed was limited to tens or hundreds of thousands of times. That limitation has been extended to a million write operations in modern EEPROMs. In an EEPROM that is frequently reprogrammed while the computer is in use, the life of the EEPROM can be an important design consideration. It is for this reason that EEPROMs were used for configuration information, rather than random access memory. http://www.tech-faq.com/eeprom.html

History


In 1978, George Perlegos at Intel developed the Intel 2816, which was built on earlier EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

 technology, but used a thin gate oxide layer so that the chip could erase its own bits without requiring a UV source. Perlegos and others later left Intel to form Seeq Technology, which used on-device charge pump
Charge pump
A charge pump is a kind of DC to DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. Charge pump circuits are capable of high efficiencies, sometimes as high as 90–95% while being electrically simple circuits.Charge pumps use some...

s to supply the high voltages necessary for programming EEPROMs.

Functions of EEPROM


There are different types of electrical interfaces to EEPROM devices. Main categories of these interface types are:
  • Serial bus
  • Parallel bus


How the device is operated depends on the electrical interface.

Serial bus devices


Most common serial interface types are SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...

, I²C
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...

, Microwire
Microwire
Microwire, often spelled μWire, is a restricted subset of SPI, or Serial Peripheral Interface Bus and a trademark of National Semiconductor. MicrowirePLUS is the equivalent of the Queued Serial Peripheral Interface.-External links:...

, UNI/O
UNI/O
The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices...

, and 1-Wire
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal. 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive...

. These interfaces require between 1 and 4 control signals for operation, resulting in a memory device in an 8 pin (or less) package.

The serial EEPROM (or SEEPROM) typically operates in three phases: OP-Code Phase
Opcode
In computer science engineering, an opcode is the portion of a machine language instruction that specifies the operation to be performed. Their specification and format are laid out in the instruction set architecture of the processor in question...

, Address Phase and Data Phase. The OP-Code is usually the first 8-bits input to the serial input pin of the EEPROM device (or with most I²C devices, is implicit); followed by 8 to 24 bits of addressing depending on the depth of the device, then data to be read or written.

Each EEPROM device typically has its own set of OP-Code instructions to map to different functions. Some of the common operations on SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...

 EEPROM devices are:
  • Write Enable (WREN)
  • Write Disable (WRDI)
  • Read Status Register (RDSR)
  • Write Status Register (WRSR)
  • Read Data (READ)
  • Write Data (WRITE)


Other operations supported by some EEPROM devices are:
  • Program
  • Sector Erase
  • Chip Erase commands

Parallel bus devices


Parallel EEPROM devices typically have an 8-bit data bus and an address bus wide enough to cover the complete memory. Most devices have chip select and write protect pins. Some microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...

s also have integrated parallel EEPROM.

Operation of a parallel EEPROM is simple and fast when compared to serial EEPROM, but these devices are larger due to the higher pin count (28 pins or more) and have been decreasing in popularity in favor of serial EEPROM or Flash.

Other devices


EEPROM memory is used to enable features in other types of products that are not strictly memory products. Products such as real-time clock
Real-time clock
A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.-Terminology:The term is used to avoid...

s, digital potentiometer
Potentiometer
A potentiometer , informally, a pot, is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used , it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on...

s, digital temperature sensor
Silicon bandgap temperature sensor
The silicon bandgap temperature sensor is an extremely common form of temperature sensor used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost...

s, among others, may have small amounts of EEPROM to store calibration information or other data that needs to be available in the event of power loss.

Failure modes


There are two limitations of stored information; endurance, and data retention.

During rewrites, the gate oxide in the floating-gate transistors gradually accumulates trapped electrons. The electric field of the trapped electrons adds to the electrons in the floating gate, lowering the window between threshold voltages for zeros vs ones. After sufficient number of rewrite cycles, the difference becomes too small to be recognizable, the cell is stuck in programmed state, and endurance failure occurs. The manufacturers usually specify the maximum number of rewrites being 106 or more.

During storage, the electrons injected into the floating gate may drift through the insulator, especially at increased temperature, and cause charge loss, reverting the cell into erased state. The manufacturers usually guarantee data retention of 10 years or more.

Related types


Flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

 is a later form of EEPROM. In the industry, there is a convention to reserve the term EEPROM to byte-wise erasable memories compared to block-wise erasable flash memories. EEPROM takes more die area than flash memory for the same capacity because each cell usually needs both a read, write and erase transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

, while in flash memory the erase circuits are shared by large blocks of cells (often 512×8).

Newer non-volatile memory technologies such as FeRAM
Ferroelectric RAM
Ferroelectric RAM is a random-access memory similar in construction to DRAM but uses a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile memory technologies that offer the same functionality as Flash memory...

 and MRAM
MRAM
Magnetoresistive Random-Access Memory is a non-volatile computer memory technology that has been under development since the 1990s. Continued increases in density of existing memory technologies – notably flash RAM and DRAM – kept it in a niche role in the market, but its proponents...

 are slowly replacing EEPROMs in some applications, but are expected to remain a small fraction of the EEPROM market for the foreseeable future.

Comparison with EPROM and EEPROM/Flash


The difference between EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

 and EEPROM lies in the way that the memory programs and erases. EEPROM can be programmed and erased electrically using field electron emission (more commonly known in the industry as "Fowler–Nordheim tunneling").

EPROMs can't be erased electrically, and are programmed via hot carrier injection
Hot carrier injection
Hot carrier injection is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to the effective temperature used to model carrier density, not to the...

 onto the floating gate. Erase is via an ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 light source, although in practice many EPROMs are encapsulated in plastic that is opaque to UV light, and are "one-time programmable".

Most NOR Flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

 is a hybrid style—programming is through hot carrier injection
Hot carrier injection
Hot carrier injection is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to the effective temperature used to model carrier density, not to the...

 and erase is through Fowler–Nordheim tunneling.

EEPROM manufacturers

  • Atmel
    Atmel
    Atmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...

  • Hitachi
    Hitachi, Ltd.
    is a Japanese multinational conglomerate headquartered in Marunouchi 1-chome, Chiyoda, Tokyo, Japan. The company is the parent of the Hitachi Group as part of the larger DKB Group companies...

  • Infineon
  • Linear Technology
    Linear Technology
    Linear Technology Corporation designs, manufactures and markets a broad line of standard high performance analog integrated circuits. Applications for the company's products include telecommunications, cellular telephones, networking products, notebook and desktop computers, video/multimedia,...

  • Macronix Int'l Co.
  • Maxwell Technologies
    Maxwell Technologies
    Maxwell Technologies is a developer and manufacturer of energy storage and power delivery-related products.-History:The company was founded in 1965 as Maxwell Laboratories, originally as a government contractor, providing advanced physics, pulsed power, space effects analysis and other research and...

  • Microchip Technology
    Microchip Technology
    Microchip Technology is an American manufacturer of microcontroller, memory and analog semiconductors. Its products include microcontrollers , Serial EEPROM devices, Serial SRAM devices, KEELOQ devices, radio frequency devices, thermal, power and battery management analog devices, as well as...

  • Mitsubishi
    Mitsubishi
    The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...

  • NXP Semiconductors
  • ON Semiconductor
    ON Semiconductor
    ON Semiconductor , is a semiconductors supplier company. Products include power and signal management, logic, discrete and custom devices for automotive, communications, computing, consumer, industrial, LED lighting, medical, military/aerospace and power applications...

  • Renesas Technology
  • ROHM
    Rohm
    ROHM Semiconductor is a Japanese electronic parts supplier based in Kyoto, Japan. ROHM was incorporated as Toyo Electronics Industry Corporation by Kenichiro Sato on September 17, 1958. The name was officially changed to Rohm in 1981 and then changed again to "ROHM Semiconductor" in January of...

  • Samsung Electronics
    Samsung Electronics
    Samsung Electronics is a South Korean multinational electronics and information technology company headquartered in Samsung Town, Seoul...

  • STMicroelectronics
    STMicroelectronics
    STMicroelectronics is an Italian-French electronics and semiconductor manufacturer headquartered in Geneva, Switzerland.While STMicroelectronics corporate headquarters and the headquarters for EMEA region are based in Geneva, the holding company, STMicroelectronics N.V. is registered in Amsterdam,...

  • Seiko Instruments
    Seiko Instruments
    , or SII, is a Japanese company, renowned for developing and commercializing semiconductor, micromechatronics, and precision timepiece technology...

  • Winbond
    Winbond
    Winbond Electronics Corporation is a Taiwan-based corporation founded in 1987 that produces semiconductors and several types of integrated circuits, most notably Dynamic RAM, Static RAM, microcontrollers, and personal computer ICs...


See also

  • NVRAM
    NVRAM
    Non-volatile random-access memory is random-access memory that retains its information when power is turned off, which is described technically as being non-volatile...

  • Flash memory
    Flash memory
    Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

  • DataFlash
    DataFlash
    DataFlash is a low pin-count serial interface for flash memory. It is an Atmel proprietary interface, compatible with the SPI standard.Information is written and read from a DataFlash chip using any microcontroller, such as the Atmel AVR, the Microchip PIC or the ARM...

  • Intel HEX
    Intel HEX
    Intel HEX is a file format for conveying binary information for applications like programming microcontrollers, EPROMs, and other kinds of chips. It is one of the oldest file formats available for this purpose, having been in use since the 1970s...

     - File format
  • SREC
    SREC (file format)
    The Motorola S-record format is an ASCII hexadecimal text encoding for binary data. It is also known as the SREC or S19 format. Each record contains a checksum to detect data that has been corrupted during transmission. The first record may include arbitrary comments such as a program name or...

    - File format