DS2784 Maxim Integrated Products, DS2784 Datasheet - Page 29

• Manufacturer Part Number: DS2784
• Description: 1-Cell Stand-Alone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

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SECRET MANAGEMENT FUNCTION COMMANDS
CLEAR SECRET [5Ah]. This command sets the 64-bit secret to all 0s (0000 0000 0000 0000h). The host must
wait t
COMPUTE NEXT SECRET WITHOUT ROM ID [30h]. This command initiates a SHA-1 computation of the MAC
and uses a portion of the resulting MAC as the next or new secret. The hash operation is performed with the
current 64-bit secret and the 64-bit challenge. Logical 1s are loaded in place of the ROM ID. 64 bits of the output
MAC are used as the new secret value. The host must allow t
calculation to complete, then wait t
command timing.
COMPUTE NEXT SECRET WITH ROM ID [33h]. This command initiates a SHA-1 computation of the MAC and
uses a portion of the resulting MAC as the next or new secret. The hash operation is performed with the current 64-
bit secret, the 64-bit ROM ID and the 64-bit challenge. 64 bits of the output MAC are used as the new secret value.
The host must allow t
DS2784 to write the new secret value to EEPROM. See Figure 10 for command timing.
LOCK SECRET [60h]. This command write protects the 64-bit secret to prevent accidental or malicious overwrite
of the secret value. The secret value stored in EEPROM becomes “final”. The host must wait t
write the lock secret bit to EEPROM. See Figure 12 for command timing.
Table 10. Secret Loading Function Commands
Clear Secret
Compute Next Secret Without
ROM ID
Compute Next Secret With
ROM ID
Lock Secret
1-Wire BUS SYSTEM
The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1-Wire bus
with multiple slaves, while a single-drop bus has only one slave device. In all instances, the DS2784 is a slave
device. The bus master is typically a microprocessor in the host system. The discussion of this bus system consists
of five topics: 64-bit net address, CRC generation, hardware configuration, transaction sequence, and 1-Wire
signaling.
64-BIT NET ADDRESS (ROM ID)
Each DS2784 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The term net address
is synonymous with the ROM ID or ROM code terms used in the DS2502 and other 1-Wire documentation. The first
eight bits of the net address are the 1-Wire family code (32h). The next 48 bits are a unique serial number. The last
eight bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 6). The 64-bit net address and the
1-Wire I/O circuitry built into the device enable the DS2784 to communicate through the 1-Wire protocol detailed in
this data sheet.
Figure 6. 1-Wire Net Address Format
EEC
for the DS2784 to write the new secret value to EEPROM. See Figure 12 for command timing.
COMMAND
MSb
8-BIT CRC
SHA
after issuing this command for the SHA calculation to complete, then wait t
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
HEX
EEC
5A
30
33
60
for the DS2784 to write the new secret value to EEPROM. See Figure 10 for
48-BIT SERIAL NUMBER
Clears the 64-bit Secret to 0000 0000 0000 0000h.
Generates new global secret.
Generates new unique secret.
Sets lock bit to prevent changes to the secret.
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SHA
FUNCTION
after issuing this command for the SHA
8-BIT FAMILY
CODE (32H)
LSb
EEC
for the DS2784 to
EEC
for the