Datasheet

DS2775/DS2776/DS2777/DS2778
2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication
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64-Bit Net Address (ROM ID)
Each DS2775–DS2778 has a unique, factory-pro-
grammed ROM ID that is 64 bits. The first 8 bits of the
net address are the product family code (3Dh). The
next 48 bits are a unique serial number. The last 8 bits
are a cyclic redundancy check (CRC) of the first 56 bits
(see Figure 22).
Authentication
The DS2776/DS2778 have an authentication feature
that is performed using a FIPS 180-compliant SHA-1
one-way hash algorithm on a 512-bit message block.
The message block consists of a 64-bit secret, a 64-bit
challenge, and 384 bits of constant data. Optionally,
the 64-bit net address replaces 64 of the 384 bits of
constant data used in the hash operation. Contact
Maxim for details of the message block organization.
The host and the DS2776/DS2778 both calculate the
result based on the mutually known secret. The result
data, known as the message authentication code
(MAC) or message digest, is returned by the
DS2776/DS2778 for comparison to the host’s result.
Note that the secret is never transmitted on the bus and
thus cannot be captured by observing bus traffic. Each
authentication attempt is initiated by the host system by
providing a 64-bit random challenge through the Write
ADDRESS (HEX) DESCRIPTION READ/WRITE
13h Accumulated Current Register LSB - 2 R
14h Age Scalar Register R/W*
15h Special Feature Register R/W
16h Full Register MSB R
17h Full Register LSB R
18h Active-Empty Register MSB R
19h Active-Empty Register LSB R
1Ah Standby-Empty Register MSB R
1Bh Standby-Empty Register LSB R
1Ch Voltage Register MSB, V
IN2
- V
IN1
R
1Dh Voltage Register LSB, V
IN2
- V
IN1
R
1Eh Cycle Counter Register R/W*
1Fh EEPROM Register R/W
20h to 2Fh User EEPROM Register, Lockable, Block 0 R/W
30h to 5Fh Reserved —
60h to 80h Parameter EEPROM Register, Lockable, Block 1 R/W
81h to AFh Reserved —
B0h Factory Gain RSGAIN Register MSB R
B1h Factory Gain RSGAIN Register LSB R
B2h to FDh Reserved —
FEh 2-Wire Command Register W
FFh Reserved —
Table 9. Memory Map (continued)
* Register value is automatically saved to EEPROM during active-mode operation and recalled from EEPROM on power-up.
8-BIT CRC 48-BIT SERIAL NUMBER
8-BIT FAMILY
CODE (3Dh)
MSb LSb
Figure 22. 1-Wire Net Address Format (ROM ID)