37.5.1.8.1 External Loop-Back Mode

The CAN can be set in External Loop-Back mode by programming the TEST.LBCK bit (TEST <4>) to ‘1’. In Loop-Back mode, the CAN treats its own transmitted messages as received messages and stores them (if they pass acceptance filtering) into an Rx Buffer or an Rx FIFO. The figure below shows the connection of signals CANx_TX and CANx_RX to the CAN in External Loop-Back mode.

This mode is provided for hardware self-test. To be independent from external stimulation, the CAN ignores acknowledge errors (the recessive bit sampled in the acknowledge slot of a data/remote frame) in Loop-Back mode. In this mode the CAN performs an internal feedback from its Tx output to its Rx input. The actual value of the CANx_RX input pin is disregarded by the CAN. The transmitted messages can be monitored at the CANx_TX pin.