SLUUB65B May 2015 – December 2022
The HDQ interface is an asynchronous return-to-one protocol where a processor sends the command code to the fuel gauge. With HDQ, the least significant bit (LSB) of a data byte (command) or word (data) is transmitted first. Note that the DATA signal on pin 12 is open-drain and requires an external pullup resistor. The 8-bit command code consists of two fields: the 7-bit HDQ command code (bits 0:6) and the 1-bit RW field (MSB bit 7). The RW field directs the fuel gauge either to:
The HDQ peripheral can transmit and receive data as either an HDQ master or slave.
HDQ serial communication is normally initiated by the host processor sending a break command to the fuel gauge. A break is detected when the DATA pin is driven to a logic-low state for a time t(B) or greater. The DATA pin should then be returned to its normal ready high logic state for a time t(BR). The fuel gauge is now ready to receive information from the host processor.
The fuel gauge is shipped in the I2C mode. TI provides tools to enable the HDQ peripheral. The HDQ Communication Basics Application Report (SLUA408) provides details of HDQ communication basics, including an alternative method to use a standard two-wire UART for single-wire HDQ communication.
If users develop their own tools to program the DFI and need to set the device to HDQ mode, the following steps are required. After writing the DFI but before sending the commands to exit ROM mode, send the following commands: