Rainbow Electronics DS1957 - Manual (Page 2)

DS1957
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ISSUING AND ACTIVATION INFORMATION
See www.ibutton.com
EXAMPLES OF ACCESSORIES
DS1410E Parallel Port Button Holder
DS1402D-DB8 iButton Dot Receptor
DS9093F
Snap-In Fob
DS9096P Self-Stick Adhesive Pad
DS9093RA Mounting Lock Ring
DS9101 Multi-Purpose Clip
CRYPTO iButton DESCRIPTION
The DS1957 Crypto iButton is a secure coprocessor residing in a stainless steel MicroCan with 1-Wire
interface. The device is addressed by matching its individual 64-bit factory-lasered registration number.
The 64-bit number consists of an 8-bit family code, a unique 48-bit serial number, and an 8-bit cyclic
redundancy check. Data is transferred serially via the 1-Wire communication protocol which requires
only a single data lead and a ground return for communication and power. Typical applications include
authentication of the person at the computer, secure transmission of E-mail, electronic notary service,
electronic cash dispenser, electronic secure monetary transactions, software authorization and usage
metering, postal metering service, electronic signature, micro-cash metering and physically secure
coprocessor array for servers.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS1957. The DS1957 has four main components: 1) 64-bit lasered ROM, 2) I/O and status registers,
3) microcomputer with 64 kbyte firmware and 134 kbyte nonvolatile data memory, and 4) arithmetic
accelerator for modular arithmetic. The device derives its power for I/O communication entirely from the
1-Wire communication line by storing energy on an internal capacitor during periods of time when the
signal line is high and continues to operate off of this “parasite” power source during the low times of the
1-Wire line until it returns high to replenish the parasite (capacitor) supply. During program execution,
the 1-Wire line must be pulled high to 5 volt via a low-impedance transistor to provide the energy for the
microcomputer and the accelerator to operate. After a time period that was agreed between bus master
and Crypto iButton, the DS1957 stops executing the program and waits for the bus master to initiate
another processing cycle and so on, until data processing is finished. The timing is based on the True
Time Clock of the DS1957 and the Real Time Clock of the bus master.
The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide
one of the six ROM Function Commands, 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM,
5) Overdrive-Skip ROM or 6) Overdrive-Match ROM. Upon completion of an Overdrive ROM
command byte executed at regular speed, the device will enter the Overdrive mode where all subsequent
communication occurs at a higher speed. These commands operate on the 64-bit lasered ROM portion of
each device and can singulate a specific device if many are present on the 1-Wire line as well as indicate
to the bus master how many and what types of devices are present. The protocol required for these ROM
Function Commands is described in Figure 6. After a ROM function command is successfully executed,
the data transfer and control functions that operate the microcomputer inside the DS1957 become
accessible and the bus master may issue any one of the nine commands specific to the DS1957. The
protocol for these commands is described in Figure 4. Unless otherwise stated, all data is read and
written least significant bit first.