I3C Broadcast Address

The Controller transmits the 7-bit Reserved I3C Broadcast Address 7’h7E after a Start condition to begin an SDR transaction on the I3C bus. 7’h7E is a reserved address in the I2C protocol, so any I2C devices on the bus will always NACK this address.

The following SDR transactions can take place after the Controller sends the 7’h7E I3C Broadcast Address:

The 7’h7E Broadcast Address can only be transmitted by the Controller (and never by any target) following a Start or Restart condition. Typically, the Controller sends the 7’h7E address in Write mode (R/W bit = 0, represented as 7'h7E/W) except in the Dynamic Address Assignment procedure when part of the transaction is in Read mode (R/W bit = 1, represented as 7'h7E/R). The Target typically ACKs a Broadcast Address from the Controller unless one of the buffer errors occur as mentioned in section Transmit and Receive Buffers, in which case the Target will NACK the request.

The Controller typically transmits the 7’h7E Broadcast Address following a Start at slower I2C speeds in Open-Drain mode since it is subject to arbitration(2). This transmission allows the I2C devices to NACK the request. Once the bus is in SDR mode, the rest of the transaction (including any future Broadcast Addresses following a Restart) can happen at faster I3C speeds in Push-Pull mode.
Important:
  1. 1.The I3C protocol allows the Controller to communicate to any I2C device (or I3C devices operating in I2C mode) even after configuring the bus to operate in I3C SDR mode by transmitting a Restart followed by the device’s Static Address. Refer to section 2Legacy IC Transaction on I3C Bus for more information.
  2. 2.Since 7'h7E is an extremely low priority address, the Controller will almost always lose arbitration if another device is transmitting another address at the same time. Refer to section I3C Address Arbitration for details.