Solution:

You can use Advantech COMTEST.EXE version 1.20 above to test your on-board RS-485 function. Test Procedure: 1. Change Jumper setting for RS-485. 2. BIOS CMOS setting: Enable COM port and modify the IRQ, I/O address if needed. 3. Connect two RS-485 port with the right cable (GND is not needed). 4. Start COMTEST.EXE 5. Modify IRQ, I/O address setting 6. Test Terminal Emulation Notice: Some CPU board or Card do not connect Tx-/Rx- and Tx+/Rx+, you must use another cable for this case.