DS2703K Maxim Integrated, DS2703K Datasheet - Page 7

• Manufacturer Part Number: DS2703K
• Description: Battery Management
• Manufacturer: Maxim Integrated
• Series: DS2703r

DS2703EVKIT
It is important for the software and the DS2703 to have identical Secrets, ROM ID’s, and Challenges so
that the software can properly verify the operation of the DS2703. If the software is not in sync with the
device, simply start with a new Secret and Load it into the device.
The DS2703 has 2 commands to compute the Next Secret. The Compute Next Secret with ID command
uses the Secret, the ROM ID and the Challenge to perform the SHA-1 encryption algorithm. The
Compute Next Secret command uses the Secret and the Challenge, but replaces the ROM ID with 0xFF’s
to perform the algorithm. The user can select which command is used by left-clicking on the appropriate
button.
Note: The user must provide a 15 Volt Programming voltage to the VPP pad of the evaluation board in
order for the Secret to be altered.
The ROM ID
The ROM ID code is unique for each DS2703 device and cannot be changed by the User. The user can
load the ROM ID of the device into the ROM ID text boxes by using the Read ROM or Search ROM
functions described in the 1 Wire Commands section.
The Challenge
The Challenge is a random 8 byte block that is used by the DS2703 to perform the SHA-1 encryption
algorithm. Each time the SHA-1 is performed, either during a Compute Next Secret or a Compute MAC
(see below) the Challenge is left in an undefined state. Therefore the user must left-click on the Write
Challenge button prior to each computation in order to get a proper SHA-1 calculation.
The user can left-click on the Randomize Challenge button to load a random challenge into the Challenge
text boxes. Left-clicking this button does not write the Challenge to the device. It is still required that the
user left-click on the Write Challenge button to write the challenge to the device.
The MAC
The MAC is the 20 byte message digest that is the result of the SHA-1 encryption algorithm. When the
Secret has been loaded properly, the ROM ID has been read, and the Challenge has been written to the
device, left-clicking on the Compute MAC or Compute MAC with ID button will perform the SHA-1
calculation, read back the results, and then display them in the MAC text boxes.
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