Yes, but only if it supports the passive Hot-Join method defined in specification Section 5.1.5.3. If the Target does not support passive Hot-Join, then see Q17.6, "Can I3C Hot-Join Target Devices be used on a Legacy I2C bus?"

Before initiating the Hot-Join Request, a Target that supports passive Hot-Join must first ensure that it is actually on an I3C Bus. This can be done by waiting for a recognizable end of an SDR Frame that ends with  a STOP. The key difference is that in order to determine that this is actually an I3C Bus, the Target must first  see an SDR Frame addressed to the Broadcast Address (7’h7E / W). Following this, the Target could either pull SDA Low to drive a START condition, or wait to see a START that another I3C Device initiates, before emitting the Hot-Join Request (i.e., arbitrating the special Hot-Join Address 7’h02 into the Arbitrable Address Header following the START).

Note: A passive Hot-Joining Target needs to see an SDR Frame that is addressed to the Broadcast Address  in order to determine that the Bus is in SDR Mode. Without this knowledge, such a Target might see  Bus activity in HDR Modes and misinterpret it as STARTs and STOPs. Alternatively, a passive  Hot-Joining Target could wait for the HDR Exit Pattern because it clearly indicates a return to SDR Mode.

The detection of an SDR Frame that is addressed to the Broadcast Address is critical because a passive Hot-Joining Target might not engage its timer or oscillator (i.e., to check for Bus Idle or Bus Available condition) until it determines that it is on an I3C Bus and that the Bus is in SDR Mode. Without this detection, such a Target will not know whether it is safe to emit the Hot-Join Request.

If the Target ensures that it is indeed on an I3C Bus in this manner, then it must observe the standard behaviors of an I3C Target that has not yet received a Dynamic Address, as defined in specification Section 5.1.2.1. The Target must acknowledge the Broadcast Address (7’h7E), which means that it is required to understand and process all required CCCs, including ENEC and DISEC. Such a Target is not eligible to respond to the ENTDAA CCC before it has emitted the Hot-Join Request at least once.

A Target that supports both standard and passive Hot-Join methods is free to either A) Initiate a START, wait for the appropriate time (i.e., Bus Idle condition), emit the Hot-Join Request, and then pull SDA Low like a standard Hot-Joining Device; or B) Wait for a START that another I3C Device emits (i.e., after waiting for Bus Idle condition).

FAQ Type: 
I3C