We are trying to use UART2 of the Apalis TK1 SOM in RX/TX only mode (no handshake) on a Ixora carrier. Our interface is connected only to the RX and TX of UART2 on header X21, all other signals open. We’ve updated the OS image to the NVIDIA Jetpack Ubuntu 14.04 and tried some basic serial transactions, however, the port behaved like it was dead. We switched to an identical carrier, prepared in an identical manner and observed the same results. We verified that the UART2 port driver configuration was “no handshake” so the RTS/CTS should be don’t care. In desperation, I tried a pullup resistor on CTS and magically, the port started to work.
In searching your forum, I noticed a similar issue someone had with the NVIDIA T30. Is there possibly a driver bug? There is a note in the Apalis datasheet to either pullup or pulldown unused UART input pins, but that seems to be stated only to ensure they don’t (electrically) float; no mention that they affect UART operation.