EEPROM (Electrically Erasable Programmable Read-Only Memory) [MiniTool Wiki]

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You may know that ROM is a kind of non-volatile memory, but do you know that EEPROM memory also belongs to non-volatile memory? In this post, MiniTool will give you some information about EEPROM.

Related post: Memory vs. Storage: Differences and How Much Do You Need?

Overview pf EEPROM

Definition

What is EEPROM memory? It is short for electrically erasable programmable read-only memory, which can also be written as E2PROM. As a type of non-volatile memory used in computers, it is integrated with microcontrollers for smart cards and remote keyless systems, and other electronic devices to store relatively small amounts of data. But it allows erasing and reprogramming individual bytes.

The EEPROM is organized as a floating gate transistor array. EEPROM can be programmed and erased in-circuit by applying special programming signals. Initially, EEPROMs were limited to single-byte operations, which made them slow, but modern EEPROMs support multi-byte page operations.

The erasure and reprogramming life of EEPROM is limited, and currently reaches one million operations in modern EEPROM. In an EEPROM that is frequently reprogrammed, the life of the EEPROM is an important design consideration.

Today, EEPROM is used in embedded microcontrollers and standard EEPROM products. EEPROM still requires a structure of 2 transistors per bit to erase the dedicated bytes in the memory, while flash memory has 1 transistor per bit to erase the area of the memory.

What’s more, since EEPROM technology is used for certain security gadgets, such as credit cards, SIM cards, keyless entry, and so on, some devices have a security protection mechanism.

History

  • In the early 1970s, some companies and organizations began to develop EEPROM.
  • In 1972, the EEPROM device was successfully manufactured
  • In 1975, NEC’s semiconductor operations unit and later NEC Electronics (now Renesas Electronics) granted the tradename EEPROM® to the Japan Patent Office. In 1978, the trademark right was granted and registered as No. 1,342,184 in Japan, which was still valid until March 2018.
  • In February 1977, Eliyahou Harari of Hughes Aircraft Company invented a new EEPROM technology, which uses the Fowler-Nordheim tunneling technology, passing through a thin layer of silicon dioxide between the floating gate and the wafer. Hughes continued to produce this new EEPROM device. But the patent cited NEC's EEPROM®
  • From 1976 to around 1978, the Intel’s team including George Perlegos made some inventions to enhance this tunneling EEPROM technology.
  • In 1978, the Intel’s team developed a 16K (2K word × 8) bit Intel 2816 device with a thin silicon dioxide layer of less than 200Å.
  • In 1980, this structure was publicly introduced in the form of FLOTOX; floating gate tunnel oxide. The FLOTOX structure improved the reliability of the erase/write cycle per byte up to 10,000 times.

Electrical Interface

EEPROM devices adopt serial or parallel interfaces for data input/output.

Serial Bus Devices

Common serial interfaces are SPI, I²C, Microwire, UNI/O, and 1-Wire. They use 1 to 4 device pins and allow devices to use 8-pin or fewer packages. A typical EEPROM serial protocol includes three phases: OP-code Phase, Address Phase, and Data Phase.

Each EEPROM device usually has its own set of OP-Code instructions, which map to different functions. Common operations on SPI EEPROM devices are:

  • Write Enable (WRENAL)
  • 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 usually possess an 8-bit data bus and an address bus that is wide enough to cover the entire memory. Most devices have chip select and write protection pins. Some microcontrollers also have integrated parallel EEPROM.

Compared with serial EEPROM, the operation of parallel EEPROM is simple and fast, but due to the higher pin count (28 pins or more), these devices are larger, and gradually become popular due to the use of serial EEPROM or flash memory.

Other Devices

EEPROM memory is used to enable functions in other types of products that are not strictly memory products. Products like real-time clocks, digital potentiometers, and digital temperature sensors may have a small amount of EEPROM for storing calibration information or other data that is available when power is turned off. Before using external and internal flash memories, it was also used on video game cartridges to save game progress and configuration.

The End

In this post, you can know what EEPROM is. It is short for electrically erasable programmable read-only memory and it often adopts serial or parallel interfaces for data input/output.

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