iButton DESCRIPTION
The DS1990A Serial Number iButton is a rugged data carrier that acts as an electronic registration number for automatic identification. The DS1990A consists of a factory-lasered, 64-bit ROM that includes an unique 48-bit serial number, an 8-bit CRC and an 8-bit Family Code (01h). Data is transferred serially via the 1-Wire protocol which requires only a single data lead and a ground return. The DS1990A is fully compatible with the DS1990 Serial Number iButton but provides the additional 1-Wire protocol capability that allows the Search ROM command to be interpreted by the DS1990A and therefore allows multiple DS1990A devices to reside on a single data line.
The durable MicroCan package is highly resistant to environmental hazards such as dirt, moisture and shock. Its compact coin-shaped profile is self-aligning with mating receptacles, allowing the DS1990A to be used easily by human operators. Accessories permit the DS1990A to be mounted on plastic key tabs, photo ID badges, printed circuit boards or any smooth surface of an object. Applications include access control, work-in-progress tracking, tool management and inventory control.

DS1990A SPECIAL FEATURES
■ Upgrade of DS1990 allows multiple Serial Number iButtons to reside on a common bus
■ Unique 48–bit serial number
■ Low-cost electronic key for access control
■ 8-bit CRC for checking data integrity
■ Can be read in less than 5 ms
■ Operating temperature range of -40°C to +85°C

COMMON iButton FEATURES
■ Unique, factory-lasered and tested 64-bit registration number (8-bit family code + 48- bit serial number + 8-bit CRC tester) assures absolute traceability because no two parts are alike
■ Multidrop controller for MicroLAN
■ Digital identification by momentary contact
■ Chip-based data carrier compactly stores information
■ Data can be accessed while affixed to an object
■ Economically communicates to bus master with a single digital signal at 16.3k bits per second
■ Standard 16 mm diameter and 1-WireTM protocol ensure compatibility with iButton family
■ Button shape is self-aligning with cup shaped probes
■ Durable stainless steel case engraved with registration number withstands harsh environments
■ Easily affixed with self-stick adhesive backing, latched by its flange, or locked with a ring pressed onto its rim
■ Presence detector acknowledges when reader first applies voltage
■ Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus, Approved under Entity Concept for use in Class 1, Division 1, Group A, B, C and D locations