Does the TX1 support communication over RS485?
The Linux kernel has many abilities regarding serial communications. The RS-485 though implies a physical device connector which is not present on the Jetson.
The serial device on the Jetson is a chip which can be set to behave like a 16450 or 16550 serial UART chip. Whatever a 16450 or 16550 can do is what the Jetson can do. I don’t know enough about RS-485 to tell you what would be required to create the RS-485 interface using this chip, but there is no direct support for the RS-485 without some sort of hardware addition. The PCIe x4 of the carrier board could be used with an add-on RS-485 adapter.