37.2.4.2.5 I3C Address Arbitration

The Address Header following a Start condition (but not a Restart condition) is subject to arbitration, meaning multiple devices on the bus may attempt to drive an address on the bus using SDA lines. The Controller may drive the SDA line to transmit the address of a device it intends to communicate with. The Target may drive the SDA line to transmit its own address while requesting for Hot-Join or In-Band Interrupt. The Address Header Arbitration process is described in Figure 37-11. The Target loses Address Arbitration when it releases the SDA line to transmit a ‘1’, but another device on the bus drives it low to transmit a ‘0’. Table 37-7 lists all the devices on an I3C bus that can participate in address arbitration and the different addresses they can drive on the bus.

Important: The arbitrable Address Header is usually transmitted in Open-Drain configuration to allow legacy I2C devices on the bus to participate in the arbitration process as well. However, the Controller may transmit some or all parts of the Address Header in Push-Pull configuration to exclude I2C devices from the transaction.
Table 37-7. Address Arbitration Summary
Device Driving SDA after Start Address Being Driven on SDA Representation
Active I3C Controller Broadcast Address/W I3C SDR transaction
Dynamic Address/W I3C Private Write transaction
Dynamic Address/R I3C Private Read transaction
Static Address/W Legacy I2C Write transaction
Static Address/R Legacy I2C Read transaction
Secondary I3C Controller (acting as an I3C Target) Dynamic Address/W Controller Role Request
Dynamic Address/R In-Band Interrupt Request
Hot-Join Address/W Hot-Join Request
I3C Target Dynamic Address/R(1) In-Band Interrupt Request
Hot-Join Address/W Hot-Join Request
I2C Target N/A N/A
Note:
  1. When this Target device is operating in Static Address SDR Mode and does not have a Dynamic Address assigned, the module will transmit its Static Address to request for an In-Band Interrupt.
  2. When multiple devices drive the address header simultaneously, the device transmitting the lowest 7-bit address + R/W bit value wins the arbitration.
  3. Should the Active Controller and the Target both drive the same 7-bit Dynamic Address + R/W bit on the bus, then each device waits for the other device to acknowledge, and a passive NACK is implied on the bus.
Figure 37-11. Address Arbitration Process