If arbitration is lost during the sending of the address packet, the Master Write Interrupt Flag (WIF in TWI.MSTATUS) and Arbitration Lost Flag (ARBLOST in TWI.MSTATUS) are both 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 TWI.MSTATUS) is set in addition to the write interrupt and arbitration lost flags.