The iButton® MultiKey (DS1991) 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 in the full data sheet). 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.
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