The DS1904 RTC iButton is a rugged real-time clock module that can be accessed with minimal hardware. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The DS1904 contains a unique 64-bit factory-lasered ROM and a real-time clock/calendar implemented as a binary counter. The durable MicroCan package is highly resistant to environmental hazards such as dirt, moisture, and shock. Accessories permit the DS1904 to be mounted on almost any 1-Wire and iButton are registered trademarks of Dallas Semiconductor.