Memory (EEPROM / Flash / RAM)
IC (Digital)
Chips that remember. EEPROM keeps small settings without power, Flash holds big code/data, RAM is fast scratch space that forgets at power-off. Endurance and interface are the gotchas.
Schematic symbol
Integrated circuit (DIP)
How memory (eeprom / flash / ram) appears in a circuit diagram.
Types & variants
Key specs
Capacity
BFrom 1 kbit EEPROMs to GB-class NAND.
Endurance
cyclesEEPROM ~1M writes, Flash 10k–100k per sector, FRAM ~10¹⁴.
Interface
I2C (simple), SPI/QSPI (fast), parallel (legacy).
Write/erase granularity
Flash erases whole sectors — plan wear levelling.
Markings
Part number: 24LC256 = 256 kbit I2C EEPROM; W25Q64 = 64 Mbit SPI flash. A1/A0 pins set the I2C address.
Standard values
24LC32–24LC512 EEPROMs; W25Q32/64/128 flash; 23LC1024 SRAM.
How to choose
Settings and counters → EEPROM or FRAM (byte-writable). Firmware, logs, assets → SPI NOR flash. High-rate logging that must survive power loss → FRAM. Mind 3.3 V vs 5 V parts.
Pinout & package
8-pin DIP/SOIC dominates: Vcc, GND, bus pins, WP (write protect), and address pins on I2C parts.
Example circuits
- 24LC256 storing calibration on an Arduino
- W25Q64 holding web assets for an ESP32
- FRAM ring-buffer data logger
Common failures
Worn-out cells after exceeding write endurance (bytes stick or flip), corrupted writes from power loss mid-write, wrong I2C address strapping reading as 'chip dead'.
How to test
Write a pattern, power-cycle, read it back. I2C scanner confirms the address; check the WP pin isn't tied active when writes silently fail.
Substitutes
Within a family, bigger parts are usually pin-compatible drop-ins (24LC64 → 24LC256). FRAM substitutes EEPROM one-for-one on many footprints.