DS28E01-100 Maxim, DS28E01-100 Datasheet - Page 13

• Manufacturer Part Number: DS28E01-100
• Description: The DS28E01-100 combines 1024 bits of EEPROM with challenge-and-response authentication security implemented with the ISO/IEC 10118-3 Secure Hash Algorithm (SHA-1)
• Manufacturer: Maxim

that legacy 1-Wire products support a standard com-
munication speed of 16.3kbps and overdrive of
142kbps. The slightly reduced rates for the DS28E01-
100 are a result of additional recovery times, which in
turn were driven by a 1-Wire physical interface
enhancement to improve noise immunity. The value of
the pullup resistor primarily depends on the network
size and load conditions. The DS28E01-100 requires a
pullup resistor of 2.2kΩ (max) at any speed.
The idle state for the 1-Wire bus is high. If for any rea-
son a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is to
resume. If this does not occur and the bus is left low for
more than 16µs (overdrive speed) or more than 120µs
(standard speed), one or more devices on the bus
could be reset.
The protocol for accessing the DS28E01-100 through
the 1-Wire port is as follows:
• Initialization
• ROM Function Command
• Memory/SHA-1 Function Command
• Transaction/Data
All transactions on the 1-Wire bus begin with an initial-
ization sequence. The initialization sequence consists
of a reset pulse transmitted by the bus master followed
by presence pulse(s) transmitted by the slave(s). The
presence pulse lets the bus master know that the
DS28E01-100 is on the bus and is ready to operate. For
more details, see the 1-Wire Signaling section.
Once the bus master has detected a presence, it can
issue one of the seven ROM function commands that
the DS28E01-100 supports. All ROM function com-
mands are 8 bits long. A list of these commands follows
(see the flowchart in Figure 10).
The Read ROM command allows the bus master to
read the DS28E01-100’s 8-bit family code, unique 48-
bit serial number, and 8-bit CRC. This command can
only be used if there is a single slave on the bus. If
more than one slave is present on the bus, a data colli-
______________________________________________________________________________________
Transaction Sequence
1-Wire ROM Function
ABRIDGED DATA SHEET
Read ROM [33h]
Initialization
Commands
1Kb Protected 1-Wire EEPROM
sion occurs when all slaves try to transmit at the same
time (open drain produces a wired-AND result). The
resultant family code and 48-bit serial number result in
a mismatch of the CRC.
The Match ROM command, followed by a 64-bit device
registration number, allows the bus master to address a
specific DS28E01-100 on a multidrop bus. Only the
DS28E01-100 that exactly matches the 64-bit registra-
tion number responds to the subsequent memory or
SHA-1 function command. All other slaves wait for a
reset pulse. This command can be used with a single
device or multiple devices on the bus.
When a system is initially brought up, the bus master
might not know the number of devices on the 1-Wire
bus or their registration numbers. By taking advantage
of the wired-AND property of the bus, the master can
use a process of elimination to identify the registration
numbers of all slave devices. For each bit of the regis-
tration number, starting with the least significant bit, the
bus master issues a triplet of time slots. On the first slot,
each slave device participating in the search outputs
the true value of its registration number bit. On the sec-
ond slot, each slave device participating in the search
outputs the complemented value of its registration num-
ber bit. On the third slot, the master writes the true
value of the bit to be selected. All slave devices that do
not match the bit written by the master stop participat-
ing in the search. If both of the read bits are zero, the
master knows that slave devices exist with both states
of the bit. By choosing which state to write, the bus
master branches in the search tree. After one complete
pass, the bus master knows the registration number of
a single device. Additional passes identify the registra-
tion numbers of the remaining devices. Refer to
Application Note 187: 1-Wire Search Algorithm for a
detailed discussion, including an example.
This command can save time in a single-drop bus sys-
tem by allowing the bus master to access the memory
functions without providing the 64-bit registration num-
ber. If more than one slave is present on the bus and,
for example, a read command is issued following the
Skip ROM command, data collision occurs on the bus
as multiple slaves transmit simultaneously (open-drain
pulldowns produce a wired-AND result).
with SHA-1 Engine
Search ROM [F0h]
Match ROM [55h]
Skip ROM [CCh]
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