Unless working in the self-test mode, a minimum of two nodes are needed on the CAN bus for the following reason: When a node transmits a frame on the CAN bus, it expects an acknowledgment (ACK) from at least one other node on the network. Any time a CAN node successfully receives a message it will automatically transmit an ACK, unless that feature has been turned off ("silent mode", where a node receives the frame, but does not provide an ACK; the bus monitoring mode in MCAN). The node that provides the ACK does not need to be the intended recipient of the frame, although it could very well be. (All active nodes on the bus will provide an ACK, regardless of whether they are the intended recipients of that frame or not).

When the transmitting node does not receive an ACK, it results in an ACK error and the transmitting node keeps re-transmitting the frame forever. The Transmit Error Counter (TEC) will increment to 128 and stop there. REC stays at 0. Node will not go bus-off. No interrupts will be generated either. If another node is brought into the network, the TEC will start decrementing (all the way to 0) with every successful transmit.