Connecting Modbus RS-485 to a CX9200 Comm4 will not operate correctly.
Modbus RTU XDriver
Serial port XDriver
Different ports support different electrical standards.
Comm1 and Comm2 of a CX9200 has RS-485 ports and can be used directly with the Modbus RTU XDriver. As a first generation controller it requires the 1st Generation driver. Second Generation X Drivers are only for the second generation controllers (bCX1, NC2 &ACX)
The comm ports also have RS-232 ports that can be used and using an external RS-232 to RS-485 converter they can support an RS-485 network.
On Comm 4 it has 2 ports they are RS-232 and RS-422 which is sometimes referred to as "4 wire RS-485". But this is not the regular 2 wire RS-485. The difference between regular RS-485 and RS-422 (4 Wire RS-485) is half and full duplex. The RS-422 with + and - connected is not a true RS-485 2 wire as the transmitted data will also be received by the transmitting controller (feedback). Regular RS-485 will turn off its receiver when it is transmitting.