The **24AA025UID** is a specialized Serial Electrically Erasable PROM (EEPROM) manufactured by Microchip Technology. It is widely used in networking and industrial applications because it comes pre-programmed with a unique **IEEE EUI-48™ node identity**. --- ## 1. Key Technical Specifications The following table summarizes the primary electrical and functional characteristics: | Parameter | Specification | | :--- | :--- | | **Memory Size** | 2 Kbit (256 x 8 bits) | | **Interface** | I2C™ Compatible (2-wire) | | **Clock Speed** | 100 kHz (Standard), 400 kHz (Fast Mode) | | **Voltage Range** | 1.7V to 5.5V | | **Operating Current** | Read: 1 mA (Max); Standby: 1 $\mu$A (Max) | | **Endurance** | 1,000,000 Erase/Write cycles | | **Data Retention** | > 200 Years | | **Package Options** | SOT-23, SOIC | --- ## 2. Distinctive Features ### A. Unique Identification (UID) The standout feature of this chip is the **Permanent Write-Protected** area (addresses `0xFA` through `0xFF`). This region contains a 48-bit Global Unique Identifier (EUI-48™), which is essential for: * MAC addresses in Ethernet/Wi-Fi devices. * Product serialization for tracking. * Inventory management. ### B. Cascading Capability The device features hardware address pins ($A_0, A_1, A_2$), allowing up to **eight** different 24AA025UID devices to share the same I2C bus without address conflicts. ### C. Write Protection While the UID is permanently locked, the rest of the memory (the lower 128 bytes) can be software write-protected or used for general data storage. --- ## 3. Pin Configuration (SOT-23 Package) | Pin Number | Name | Function | | :--- | :--- | :--- | | 1 | **SCL** | Serial Clock Input | | 2 | **Vss** | Ground | | 3 | **SDA** | Serial Data (Bi-directional) | | 4 | **A1** | User-defined Address Bit 1 | | 5 | **A2** | User-defined Address Bit 2 | | 6 | **Vcc** | Power Supply | --- ## 4. Example: Reading Data (Pseudo-Code) To read the UID from the chip using an I2C library, the logic follows this structure: ```cpp // Example I2C Read for UID starting at address 0xFA Wire.beginTransmission(0x50); // Standard I2C address for EEPROM Wire.write(0xFA); // Point to the UID starting register Wire.endTransmission(); Wire.requestFrom(0x50, 6); // Request 6 bytes (48-bit UID) while(Wire.available()) { byte macByte = Wire.read(); // Process the MAC address byte } ``` ---