Issue
Comm4 on the NC2 is RS-422, will this operate as RS-485 if the TX & RX lines are linked?
Environment
CX9680 NCII with Modbus RTU X Driver
XDriver
Cause
Linking the TX & RX lines can cause the transmitted data to be fed back into the transmitting controller.
Resolution
Yes, you can use comm 4 as a Modbus RTU X Driver to talk to 3rd party RS-485 devices.
The Netcontroller II Comm 4 is defined as an RS-485/ RS-422 port and the X Driver will close off the RX port using the RTS line while it is transmitting.
The loopback required for a 2 core screened cable is:
- Connect TX+ to RX+
- Connect TX- to RX-
- Use shield connection
Note: If communications are still not able to be established, confirm that the Comm4 configuration in the Netcontroller II's web configuration page has been changed from the default RS-422 to RS-485.