DS1961S
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ORDERING INFORMATION
DS1961S-F5 F5 iButton
DS1961S-F3 F3 iButton
EXAMPLES OF ACCESSORIES
DS1963S SHA Coprocessor and Button
DS9096P Self-Stick Adhesive Pad
DS9101 Multipurpose Clip
DS9093RA Mounting Lock Ring
DS9093A Snap-In Fob
DS9092 iButton Probe
iButton DESCRIPTION
The DS1961S 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. Data is transferred serially through the 1-Wire protocol, which requires only a single data lead
and a ground return. The DS1961S 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 transfers the data to its final memory location, provided that the DS1961S receives
a matching 160-bit MAC. The computation of the MAC involves the secret and additional data stored in
the DS1961S 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 MACs when reading a memory page
or to compute a new secret, instead of loading it.
The DS1961S understands a unique command "Refresh Scratchpad." Proper use of a refresh sequence
after a copy scratchpad operation reduces the number of weak bit failures in a touch environment (see the
Writing with Verification section). The refresh sequence also provides a means to restore functionality in
a device with bits in a weak state.
Each DS1961S 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 to be easily used by human
operators. Accessories permit the DS1961S to be mounted on almost any surface including plastic key
fobs and photo-ID badges.
APPLICATIONS
The DS1961S can be used for different purposes such as secure access control, user/product authentica-
tion, after-market management of consumables, and as monetary tokens in electronic payment systems.
As carrier of electronic cash (eCash), the DS1961S can store up to three monetary files or "purses" of a
single service provider, which make the device well suited for company-sized single-secret applications
such as cafeteria, copy machines, and access control at entertainment parks or private clubs. For increased
security or if the processing power of the host microcontroller is insufficient, a DS1963S can be used as
secure coprocessor to verify MACs generated by the DS1961S or to compute MACs needed for writing
to the DS1961S.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS1961S. The DS1961S has five main data components: 1) 64-bit lasered ROM, 2) 64-bit scratchpad,
3) four 32-byte pages of EEPROM, 4) 64-bit register page, 5) 64-bit secrets memory, and 6) a 512-bit
