BQ27425-G2_15 Datasheet, PDF (23/39 Pages) Texas Instruments – Fuel Gauge With Integrated Sense Resistor

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bq27425-G2
SLUSB23B – OCTOBER 2012 – REVISED JUNE 2015
Reading and writing subclass data are block operations up to 32 bytes in length. If, during a write, the data
length exceeds the maximum block size, then the data is ignored.
None of the data written to memory are bounded by the fuel gauge, the values are not rejected by the fuel
gauge. Writing an incorrect value may result in hardware failure due to firmware program interpretation of the
invalid data. The data written to NVM blocks is not persistent, so a power-on reset does resolve the fault.
8.5.4 Access Modes
The fuel gauge supports SEALED and UNSEALED access modes to control data NVM access permissions
according to Table 8.
Table 8. Data NVM Access
SECURITY MODE
UNSEALED
SEALED
DATA NVM
RW
None
MANUFACTURER
INFO
RW
R
8.5.4.1 Sealing and Unsealing Data Blocks
The fuel gauge implements a key-access security scheme to transition from a SEALED state to the UNSEALED
state. Devices are shipped from the factory in the UNSEALED state and should be SEALED before use in end-
equipment. The Sealed to Unseal key can only be updated in the UNSEALED state.
To SEAL from UNSEALED: The host sends the SEALED subcommand 0x0020 to the Control( ) register. After
receiving the SEALED subcommand, the CONTROL_STATUS [SS] bit is set within 2 seconds.
To UNSEAL from SEALED: Host sends the keys to the Control( ) register. The keys must be sent
consecutively, with no other data written to Control( ).
NOTE
To avoid conflict with normal subcommands, the keys must be different from the codes
presented in the CNTL DATA column of the Table 4 table.
The first word is Key 0 and the second word is Key 1. The order of the keys sent are Key 1 followed by Key 0.
The order of the bytes for each key entered through the Control( ) command is the reverse of what is read from
the part. For example, if the 4-byte Sealed to Unseal key is 0x56781234, key 1 is 0x1234 and key 0 is 0x5678.
So, the host should write 0x3412 followed by 0x7856 to unseal the part. After receiving the correct key sequence
the CONTROL_STATUS [SS] bit is cleared.
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