The iButton^® 256-bit EEPROM (DS1971) is a rugged read/write data carrier that identifies and stores relevant information about the product or person to which it is attached. This information can be accessed with minimal hardware: for example, a single port pin of a microcontroller. The DS1971 consists of a factory-lasered registration number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (14H) plus 256 bits of EEPROM. The power to program and read the DS1971 is derived entirely from the 1-Wire^® communication line. Data is transferred serially via the 1-Wire protocol which requires only a single data lead and a ground return. The 48-bit serial number that is factory-lasered into each DS1971 provides a guaranteed unique identity which allows for absolute traceability. The durable MicroCan package is highly resistant to harsh environments such as dirt, moisture, and shock. Its compact button-shaped profile is self-aligning with cup-shaped receptacles, allowing the DS1971 to be used easily by human operators or automatic equipment. Accessories permit the DS1971 to be mounted on printed circuit boards, plastic key fobs, photo-ID badges, ID bracelets, and many other objects. Applications include work-in-progress tracking, electronic travelers, access control and storage of calibration constants.