27.3.4.2.2.1 Case M1: Arbitration Lost or Bus Error during Address Packet

If arbitration is lost during the sending of the address packet, both the Master Write Interrupt Flag (WIF in TWIn.MSTATUS) and Arbitration Lost Flag (ARBLOST in TWIn.MSTATUS) are set. Serial data output to the SDA line is disabled, and the SCL line is released. The master is no longer allowed to perform any operation on the bus until the bus state has changed back to idle.

A bus error will behave in the same way as an arbitration lost condition, but the Bus Error Flag (BUSERR in TWIn.MSTATUS) is set in addition to the write interrupt and arbitration lost flags.