ZHCSD75D March 2014 – January 2018
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. 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 through 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 then is returned to its normal ready logic high 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.