SWRU626 December 2025 CC3501E , CC3551E
To enable write access to register TEST, bit CCCR.TEST has to be set to one. This allows the configuration of the test modes and test functions.
Four output functions are available for the CAN transmit pin DCAN_TX by programming TEST.TX. Additionally to its default function – the serial data output – it can drive the CAN Sample Point signal to monitor the DCAN’s bit timing and it can drive constant dominant or recessive values. The actual value at pin DCAN_RX can be read from TEST.RX. Both functions can be used to check the CAN bus’ physical layer.
Due to the synchronization mechanism between CAN clock and Host clock domain, there may be a delay of several Host clock periods between writing to TEST.TX until the new configuration is visible at output pin DCAN_TX. This applies also when reading input pin DCAN_RX via TEST.RX.
Test modes should be used for production tests or self test only. The software control for pin DCAN_TX interferes with all CAN protocol functions. It is not recommended to use test modes for application.