I wrote a code for this microcontroller to test the CAN protocol, and it worked successfully in loopback test mode—data was transmitted and received correctly without using any external CAN transceiver. Then, I switched the CAN mode from loopback to normal mode and physically connected the TX and RX pins together using a wire.
However, with the same code (only changing the test mode), I noticed that in Live Watch, the TX pin shows activity (data being transmitted), but the RX pin shows nothing—no data being received. I even checked the signals on an oscilloscope, and the waveforms on TX and RX were identical, confirming that the signal is physically present on both lines. Yet, according to the software, no data is received.
This led me to wonder: since some microcontrollers support external loopback modes while others do not, could it be that this microcontroller does not support external loopback in normal mode by simply wiring TX and RX together? Is that correct?
