25.2.3.7.1 Slave Mode Bus Collision
A slave receives a read request and begins shifting data out on the SDA line. If a bus collision is detected and the Slave Mode Bus Collision Detect Enable (SBCDE) bit is set, the Bus Collision Interrupt Flag (BCLxIF) bit of the PIRx register is set. Once a bus collision is detected, the slave goes Idle and waits to be addressed again. User software can use the BCLxIF bit to handle a slave bus collision.