The DS1961S-002/2-F5 combines 1024 bits of EEPROM, a 64-bit secret, an 8-byte register/control page with up to five user read/write bytes, a 512-bit SHA-1 engine and a fully featured 1-Wire interface in a rugged iButton device. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The DS1961S-002/2-F5 has an additional memory area called the scratchpad that acts as a buffer when writing to the main memory, the register page or when installing a new secret. Data is first written to the scratchpad from where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to its final memory location, provided that the DS1961S-002/2-F5 receives a matching 160-Bit message authentication code (MAC). The computation of the MAC involves the secret and additional data stored in the DS1961S-002/2-F5 including the device's Identity Register. Only a new secret can be loaded without providing a MAC. The SHA-1 engine can also be activated to compute 160-bit MAC when reading a memory page or to compute a new secret, instead of loading it. The DS1961S-002/2-F5 understands a unique command "Refresh Scratchpad." Proper use of a refresh sequence (see Writing with Verification section) after a copy scratchpad operation reduces the number of weak bit failures in a touch environment. The refresh sequence also provides a means to restore functionality in a device with bits in a weak state. Each DS1961S-002/2-F5 has its own 64-bit ROM registration number that is factory lasered into the chip to provide a guaranteed unique identity for absolute traceability. The durable stainless steel 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 DS1961S-002/2-F5 to be easily used by human operators. Accessories permit the DS1961S-002/2-F5 to be mounted on almost any surface including plastic key fobs and photo-ID badges.
Feature
- 1128 bits of 5V EEPROM memory partitioned into four pages of 256 bits, a 64-bit write-only secret and up to five general purpose read/write registers
- Write access requires knowledge of the secret and the capability of computing and transmitting a 160-bit MAC as authorization
- Secret and data memory can be write-protected (all or page 0 only) or put in EPROM-emulation mode ("write to 0", page 1)
- On-chip 512-bit SHA-1 engine to compute 160-bit MAC and to generate secrets
- Reads and writes over a wide voltage range of 2.8V to 5.25V from -40°C to +85°C
- Communicates to host with a single digital signal at 14.1kb per second using 1-Wire protocol
- On-chip 16-bit CRC generator for safeguarding data transfers
- Overdrive mode boosts communication speed to 125kbps
- Operating temperature range from -40°C to +85°C
- Minimum 10 years of data retention at 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 1-Wire net
- Digital identification and information by momentary contact
- Chip-based data carrier compactly stores information
- Data can be accessed while affixed to object
- 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
