To enable write access to the MCAN Test register (MCAN_TEST) (see Section 7.6), bit MCAN_CCCR.TEST must be set. This allows the configuration of the test modes and test functions.
Four output functions are available for the CAN transmit pin CANTX by programming MCAN_TEST.TX. Additionally to its default function – the serial data output – it can drive the CAN Sample Point signal to monitor the MCAN’s bit timing and it can drive constant dominant or recessive values. The actual value at pin CANRX can be read from MCAN_TEST.RX. Both functions can be used to check the CAN bus’ physical layer.
Due to the synchronization mechanism between CAN clock and system bus clock domain, there may be a delay of several system bus clock periods between writing to MCAN_TEST.TX until the new configuration is visible at output pin CANTX. This applies also when reading input pin CANRX via MCAN_TEST.RX.