37.2.4.2.3 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:

Broadcast Common Command Code (CCC) Write Transaction
Direct CCC Read/Write Transaction
Private Read/Write Transaction
Dynamic Address Assignment
Legacy I²C Transaction⁽¹⁾

The 7’h7E Broadcast Address can only be transmitted by the Active 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). Table 37-6 shows the different conditions when this Target module ACK/NACKs the Broadcast Address on the bus.

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:

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 the Legacy I²C Transaction on I3C Bus section for more information.
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 the I3C Address Arbitration section for details.