9 Device Configuration
9.1 Commands and Subcommands
The BQ76942 device includes support for direct commands and subcommands. The direct commands are
accessed using a 7-bit command address that is sent from a host through the device serial communications
interface and either triggers an action, or provides a data value to be written to the device, or instructs the device
to report data back to the host. Subcommands are additional commands that are accessed indirectly using the
7-bit command address space and provide the capability for block data transfers. For more information on the
commands and subcommands supported by the device, refer to the
BQ76942 Technical Reference Manual
9.2 Configuration Using OTP or Registers
The BQ76942 device includes registers, with values which are stored in the RAM and can be loaded
automatically from one-time programmable (OTP) memory. At initial power-up, the device loads OTP settings
into registers, which are used by the device firmware during operation. The recommended procedure is for the
customer to write settings into OTP on the manufacturing line, in which case the device will use these settings
whenever it is powered up. Alternatively, the host processor can initialize registers after power-up, without using
the OTP memory, but the registers will need to be reinitialized after each power cycle of the device. Register
values are preserved while the device is in NORMAL, SLEEP, or DEEPSLEEP modes. If the device enters
SHUTDOWN mode, all register memory is cleared, and the device will return to the default parameters (or the
OTP configuration if that has been programmed) when powered again. See the
for more details.
9.3 Device Security
The BQ76942 device includes three security modes: SEALED, UNSEALED, and FULLACCESS, which can be
used to limit the ability to view or change settings.
• In SEALED mode, most data and status can be read using commands and subcommands, but only selected
settings can be changed. Data memory settings cannot be changed directly.
• UNSEALED mode includes SEALED functionality, and also adds the ability to execute additional
subcommands, and read and write data memory.
• FULLACCESS mode allows capability to read and modify all device settings, including writing OTP memory.
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
), 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
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.
9.4 Scratchpad Memory
The BQ76942 device integrates a 32-byte scratchpad memory which can be used by the customer for storing
manufacturing data, such as serial numbers, production or test dates, and so forth. The scratchpad data can be
written into OTP memory on the customer production line. This data can only be written while in FULLACCESS
mode, although it can be read in all modes.
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
Copyright © 2021 Texas Instruments Incorporated
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