EEPROM

An EEPROM is a type of semiconductor memory that stores data permanently even when power is removed from the device. Unlike RAM, which loses everything the moment electricity stops, an EEPROM holds its contents indefinitely until deliberately overwritten. This makes it essential in utility equipment, industrial controllers, and field devices that need to preserve calibration data, configuration settings, or logged events across power cycles.

The core function relies on floating-gate transistors: each memory cell uses a specially designed transistor that traps electrical charge in an isolated region. To write data, a high voltage pulse injects electrons into the floating gate. To erase, another pulse removes them, allowing the cell to be reused. Standard EEPROMs operate at byte level, meaning you can erase and rewrite individual bytes rather than entire blocks, which distinguishes them from flash memory used in USB drives or SD cards.

Practical use in industrial settings

In smart meters, EEPROM stores consumption history, billing dates, and meter ID when power fails. Frequency drives use EEPROM to remember tuning parameters so technicians do not reconfigure them after a shutdown. RTU units in substations depend on EEPROM to retain alarm thresholds, time-of-use schedules, and event logs. Typical capacities range from a few kilobytes to a few megabytes in modern devices.

The write speed matters in field work: EEPROMs typically require 5 to 10 milliseconds per byte, much slower than writing to RAM. This means frequent logging creates a bottleneck; devices often buffer data in RAM and write to EEPROM periodically or on triggered events. The write cycle limit is another constraint: standard EEPROMs tolerate around 100,000 to 1,000,000 erase-write cycles before degradation, so applications requiring constant rewriting are poor candidates.

EEPROMs appear in two-wire or three-wire serial interfaces (I2C or SPI protocols), allowing microcontrollers to read and update them without discrete circuit complexity. This simplicity kept them prevalent even as flash memory cost fell, because existing designs and infrastructure remain efficient. In energy applications specifically, the byte-level access suits the granular updates needed for tariff adjustments and meter recalibration in the field.