SLUUCF2C January 2021 – May 2022 BQ769142
The HDQ interface is an asynchronous return-to-one protocol where a processor communicates with the BQ769142 device using a single-wire connection to either the ALERT pin (Settings:Configuration:Comm Type = 3) or the HDQ pin (Settings:Configuration:Comm Type = 4). Note that the selected pin must be configured for use as the HDQ interface. Both the controller (host device) and responder (BQ769142) drive the HDQ interface using an open-drain driver, with a pull-up resistor from the HDQ interface to a supply voltage required on the circuit board. The BQ769142 device can be changed from the default I2C communication mode to HDQ communication mode by sending the 0x7C40 SWAP_TO_HDQ() subcommand (at which point the device switches to HDQ mode using the ALERT pin immediately). Alternatively, the mode can be changed by setting the Settings:Configuration:Comm Type configuration register in CONFIG_UPDATE mode, then exiting CONFIG_UPDATE mode, then sending the 0x29BC SWAP_COMM_MODE() subcommand, at which point the device switches to the selected mode.
With HDQ, the least significant bit (LSB) of a data byte (command) or word (data) is transmitted first.
The 8-bit command code consists of two fields: the 7-bit HDQ command code (bits 0–6) and the 1-bit R/W field (MSB Bit 7). The R/W field directs the device to do one of the following:
The HDQ peripheral on the BQ769142 device can transmit and receive data as an HDQ responder only.
The return-to-one data bit frame of HDQ consists of the following sections: