SLUSE14A December 2020 – February 2021 BQ76942
The BQ76942 device includes three security modes: SEALED, UNSEALED, and FULLACCESS, which can be used to limit the ability to view or change settings.
Selected settings in the device can be modified while the device is in operation through supported commands and subcommands, but in order to modify all settings, the device must enter CONFIG_UPDATE mode (see CONFIG_UPDATE Mode), which stops device operation while settings are being updated. After the update is completed, operation is restarted using the new settings. CONFIG_UPDATE mode is only available in FULLACCESS mode.
The BQ76942 device implements a key-access scheme to transition among SEALED, UNSEALED, and FULLACCESS modes. Each transition requires that a unique set of keys be sent to the device through subcommands. Refer to the BQ76942 Technical Reference Manual for more details.
The device provides additional checks which can be used to optimize system robustness, including subcommands which calculate the digital signature of the integrated instruction ROM and data ROM. These signatures should never change for a particular product. If these were to change, it would indicate an error, either that the ROM had been corrupted, or the readback of the ROM or calculation of the signature experienced an error. An additional subcommand calculates a digital signature for the static configuration data (which excludes calibration values) and compares it to a stored value, returning a flag if the result does not match.