iButton DESCRIPTION
The DS1991 MultiKey iButton is a rugged read/write data carrier that acts as three separate electronic keys, offering 1,152 bits of secure, nonvolatile memory. Each key is 384 bits long with distinct 64-bit password and public ID fields (Figure 1). The password field must be matched in order to access the secure memory. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The 512-bit scratchpad serves to ensure integrity of data transfers to secure memory. Data should first be written to the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to the secure memory. This process ensures data integrity when modifying the memory. A 48-bit serial number is factory lasered into each DS1991 to provide a guaranteed unique identity which allows for absolute traceability. The family code for the DS1991 is 02h. The durable MicroCan package is highly resistant to environmental hazards such as dirt, moisture and shock. Its compact button-shaped profile is self-aligning with mating receptacles, allowing the DS1991 to be easily used by human operators. Accessories permit the DS1991 to be mounted on plastic key fobs, photo-ID badges, printed-circuit boards or any smooth surface of an object. Applications include secure access control, debit tokens, work-in-progress tracking, electronic travelers and proprietary data.

SPECIAL FEATURES
■ 1,152-bit secure read/write, nonvolatile memory
■ Secure memory cannot be deciphered without matching 64-bit password
■ Memory is partitioned into 3 blocks of 384 bits each
■ 64-bit password and ID fields for each memory block
■ 512-bit scratchpad ensures data transfer integrity
■ Operating temperature range: -40°C to +70°C
■ Over 10 years of data retention

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 and information by momentary contact
■ Chip-based data carrier compactly stores information
■ Data can be accessed while affixed to object
■ Economically communicates to bus master with a single digital signal at 16.3k bits per second
■ Standard 16 mm diameter and 1-Wire 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
■ 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 I, Division 1, Group A, B, C and D Locations