What Is EEPROM?
EEPROM (Electrically Erasable Programmable ROM) is a persistent memory that can be erased and rewritten with an electrical signal. It's a flexible member of the ROM family.
How Does It Work?
Data is stored with an electric charge held on an insulated (floating) gate. The presence/absence of charge determines the bit and is preserved even when power is cut; that is, it's persistent.
The Key Property: Byte Access
EEPROM's difference from Flash is that it can erase and write data at the individual byte level. This is very useful for frequently updating small settings.
| Property | EEPROM | Flash |
|---|---|---|
| Erase unit | Byte | Block/page |
| Capacity | Small | Large |
| Cost/bit | High | Low |
Write Endurance
EEPROM has a limited erase/write cycle (typically 100 thousand – 1 million). Writing to the same cell too often exhausts the life; so wear leveling is applied in a good design.
Where Is It Used?
Device settings, calibration values, serial numbers, small persistent data inside an MCU and external I2C EEPROM chips.
External and Internal EEPROM
Many microcontrollers include a small internal EEPROM; when more persistent space is needed, external EEPROM chips connected over I2C or SPI are used. External chips offer higher capacity but the access speed is limited by the interface's speed.
Common Mistakes
- Constant writing: frequent writing exhausts the write endurance quickly.
- Using it for big data: its capacity is small, Flash suits big data.
- Ignoring the write time: writing is slower than RAM, so time it.
Frequently Asked Questions
Is EEPROM the same as Flash?+
How long does it keep data?+
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