SLUUCO5A december 2022 – august 2023 BQ34Z100-R2
The HDQ communication engine is reset if the HDQ line is held low for longer than the 190-µs minimum break time, t(B). If the host does not get an expected response from the HDQ target or if the host needs to restart a communication before it is complete, the host can hold the HDQ line low and generate a break to reset the communication engine. The next communication can begin after the 40-μs minimum break recovery time, t(BR). Figure 9-2 illustrates break timing.
If the HDQ line is disconnected and reconnected, unpredictable bit values may be input to the HDQ engine, leaving it in a non-reset state. It may be possible for the HDQ line to be disconnected during the middle of a communication. If HDQ communications are interrupted or unexpected transients occur on the HDQ line and there are no periodic breaks to reset the communication engine, it is possible for the HDQ target engine to perform an incorrect command, including an unintended write.
The most robust design practice for reliable HDQ communication is to precede each communication with a break. This ensures that the engine is reset before each communication, and minimizes the risk of unintended writes and/or reading incorrect data. Figure 9-1 illustrates a typical HDQ read cycle following a break.