Write access to the Test Register has to be enabled by setting bit CCCR[TEST] to 1 . All Test Register functions are set to their reset values when bit CCCR[TEST] is reset. Loop Back mode and software control of Tx pin FDCANx_TX are hardware test modes. Programming TX differently from 00 may disturb the message transfer on the CAN bus.
LBCK | LBCK |
TX | TX |
RX | RX |