This means that the node that transmits the first 1 loses arbitration. A node that loses arbitration re-queues its message for later transmission and the CAN frame bit-stream continues without error until only one node is left transmitting. By using this process, any node that transmits a logical 1 when another node transmits a logical 0 'drops out' or loses the arbitration. When a node transmits a logical 1 but sees a logical 0, it realizes that there is a contention and it quits transmitting. If a logical 0 is being transmitted by one or more nodes, and a logical 1 is being transmitted by one or more nodes, then a logical 0 is seen by all nodes including the node(s) transmitting the logical 1. If a logical 0 is transmitted by all transmitting node(s) at the same time then a logical 0 is seen by all nodes. If a logical 1 is transmitted by all transmitting nodes at the same time a logical 1 is seen by all of the nodes, including both the transmitting node(s) and receiving node(s). This is why some call CAN synchronous, however it is in fact asynchronous as the data is transmitted without a clock signal.Īs well as receivers all needing to always listen to the data on the CAN network, the transmitting node must also to so it can detect if its transmission is colliding with another node. Uses a lossless bit-wise arbitration method of contention resolution which requires all nodes on the CAN network to be synchronized to sample every bit on the CAN network at the same time. If you see RX low when TX isn't low then you have another device transmitting at the same time or if your TX pulses simply appear longer then you probably don't have correct bus termination. RX should exactly match TX when transmitting and it is analyzed by the CAN peripheral to see if another device on the bus is transmitting (Low) at the same time.

The CAN bus TX line (pre transceiver) idles high. High = recessive bus state (bus not driven), Low = dominant bus state (bus is driven by transceiver) Microcontroller CAN Bus Pins (Pre CAN Transceiver) CAN bus ('Controller Area Network') is widely used in the automotive, aerospace, maritime, industrial and medical industries.

Can bus high and low