BQ27425-G2_14 Datasheet, PDF (16/35 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated Sense Resistor

bq27425-G2
SLUSB23A – OCTOBER 2012 – REVISED FEBRUARY 2013
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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 bq27425, 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 persistent, so a power-on reset does not resolve the fault.
ACCESS MODES
The bq27425 supports SEALED and UNSEALED access modes to control data NVM access permissions
according to Table 6.
Table 6. Data NVM Access
Security Mode
UNSEALED
SEALED
Data NVM
R/W
None
Manufacturer Info
R/W
R
SEALING/UNSEALING DATA BLOCKS
The bq27425 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 prior to 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 command, 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 2 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 an 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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