EEPROM
EEPROM (also written E2PROM and pronounced "e-e-prom", "double-e-prom" or "e-squared-prom") stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers and other electronic devices to store relatively small amounts of data but allowing individual bytes to be erased and reprogrammed.
EEPROMs are organized as arrays of floating-gate transistors. EEPROMs can be programmed and erased in-circuit, by applying special programming signals. 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 for erasing and reprogramming, now reaching a million operations in modern EEPROMs. In an EEPROM that is frequently reprogrammed while the computer is in use, the life of the EEPROM is an important design consideration.
Unlike most other kinds of non-volatile memory, an EEPROM typically allows bytes to be read, erased, and re-written individually.
Eli Harari at Hughes Aircraft invented the EEPROM in 1977 utilising Fowler-Nordheim tunneling through a thin floating gate. Hughes went on to produce the first EEPROM devices. In 1978, George Perlegos at Intel developed the Intel 2816, which was built on earlier EPROM technology, but used a thin gate oxide layer enabling the chip to erase its own bits without a UV source. Perlegos and others later left Intel to form Seeq Technology, which used on-device charge pumps to supply the high voltages necessary for programming EEPROMs.
EEPROM devices use a serial or parallel interface for data input/output.
The common serial interfaces are SPI, I²C, Microwire, UNI/O, and 1-Wire. These use from 1 to 4 device pins and allow devices to use packages with 8-pins or less.
A typical EEPROM serial protocol consists of three phases: OP-Code Phase, 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 the read or write data.
...
Wikipedia