1. Check the TCP endpoint
Confirm the IP address and port. Make sure the device server, gateway, or TCP service is powered on and reachable from the Windows machine running the bridge.
2. Check firewall and routing
Local firewall rules, VPN routing, VLAN boundaries, and plant network rules can block TCP traffic. Test connectivity before changing serial settings.
3. Check the COM port
Only one application can usually open a COM port at a time. Close terminal tools, vendor utilities, and background services that may already be holding the virtual port.
4. Check protocol expectations
A TCP connection can be established even when the application protocol is wrong. Confirm whether the remote device expects raw TCP, RFC2217, Modbus RTU over TCP, or a vendor-specific frame format.
5. Check serial settings
- Baud rate.
- Parity.
- Data bits.
- Stop bits.
- Flow control.
6. Test recovery
Restart the remote device or disconnect the network briefly. A production bridge should recover cleanly when the device or network comes back.
What to record for support
Save the COM port number, IP address, TCP port, bridge mode, connection status, Windows version, device model, and a short description of the test command or application action that fails.