External Loop Back Mode

The MCAN can be set in External Loop Back mode by setting the bit MCAN_TEST.LBCK. In Loop Back mode, the MCAN 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 CANTX and CANRX to the MCAN in External Loop Back mode.

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