SFFS138 December   2021 TCAN1164-Q1

 

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5.3.1.4 SM-4: CAN TXD pin dominant state timeout; (tTXD_DTO)

The device supports dominant state time out (DTO). This is an internal function based upon the TXD path. The TXD DTO circuit prevents the local node from blocking network communication in event of a hardware or software failure where TXD is held dominant (LOW) longer than the time out period tTXD_DTO. The TXD DTO circuit is triggered by a falling edge on TXD. If no rising edge is seen before the time out constant of the circuit, tTXD_DTO, the CAN driver is disabled. This frees the bus for communication between other nodes on the network. The CAN driver is re-activated when a recessive signal (HIGH) is seen on TXD terminal; thus, clearing the dominant time out. The receiver remains active and the RXD terminal reflects the activity on the CAN bus and the bus terminals is biased to recessive level during a TXD DTO fault.