Jetson Nano: pselect timeout when working with USB to RS485 adapter (ch341)

Hey all!

I’ve been trying to read data from Autonics TK-4S temperature controller connected to Jetson Nano via RS485 to USB adapter (ch341). I can read data from both my Linux laptop using minimodbus Python module and from my Windows PC using Simply Modbus. Both computers use the same connection to the same temperature controller and the same parameters sent to the controller.
However, when I try to start the same script that worked on my laptop on my Jetson Nano, it cannot receive any signal and falls with NoResponseError: No communication with instrument (no answer).
I invoked strace on the python running the script and saw that it successfully opens the /dev/ttyUSB0 file, but breaks down on pselect – it fails with timeout regardless of set timeout.
Is there anyone with the same problem?

Hi @Polzovatel3366,

Welcome to the NVIDIA Developer forums! You actually posted in the Cumulus Linux category, this should be placed in the Jetson Nano section. I can move it over for you.

Tom K

hello Polzovatel3366,

please check Jetson Nano Product Design Guide, and please check the 11.3 UART chapter for the UART Connections.
the serial port on the Nano side register is as ttyTHS*, you may check $ dmesg | grep THS for reference,

Please, do. Thanks a lot!

Well, yes, but I am trying to connect the temperature controller via USB-RS485, not via the UART1 interface on the Nano itself. Moreover, opening /dev/ttyTHS1fails because there is no device connected.

Are you sure that when I am using USB adapter I do not need to use /dev/ttyUSB0? On all of my other devices (e.g. Raspberry Pi, my laptop) I am using /dev/ttyUSB0 and everything just works.

which Jetson interface you’re using?


I am connecting USB to RS485 adapter to the USB port of Jetson Nano. Since in dmesg I see a message something like “UART interface connected to ttyUSB0”, I guess that the driver of the connector itself (ch341) works just fine.

And again, the adapter is not faulty, if I connect it to my laptop, it works flawlessly and I can read information from the connected sensor just fine.

please refer to this topic,

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