On the second Windows server, RealPort reports “Could not open COM port” while the first server receives serial data. Configure port sharing for the TS 4 serial port so multiple Windows hosts can read from it; adding another RealPort client without changing the sharing configuration will not solve the conflict.
Check the second host’s COM-port error first
Use the observed connection order to narrow the fault:
| Symptom | Likely cause to check |
|---|---|
| The first Windows server opens the RealPort COM port and receives data; the next gets “Could not open COM port.” | The TS 4 port is not configured for multiple-client sharing. |
| Neither Windows server can open the COM port. | Check the basic RealPort connection and port configuration before investigating sharing. |
| Both clients connect, but one receives no data or the data is incomplete. | Check that the shared-port mode and client use match the intended read-only arrangement. |
First confirm that one host can open the COM port and receive the incoming serial stream. That rules out a total failure of the serial source or the initial RealPort path. Then test the second host; its failure only after the first has connected points to a sharing limitation rather than a bad Windows COM-port number.
Understand why the second RealPort client fails
RealPort presents a serial device through a Windows COM port, but multiple computers opening that logical port do not automatically become independent readers. The TS 4 port must support and be configured for the intended shared access. Without that configuration, the first client can hold the connection and a later client can be refused.
For this use case, treat the serial input as a stream that multiple hosts need to observe. Port sharing is the relevant TS 4 feature identified for this arrangement. Do not confuse sharing the serial data with opening a COM port on each host: the host-side driver still needs a valid RealPort connection, and the device-side serial port must be set up for sharing.
Configure TS 4 port sharing for read-only clients
- Identify the TS 4 port receiving the serial data. Record its current port mode and the RealPort COM port mapping used by the working Windows server.
- Open the TS 4 port configuration and locate its port-sharing settings. Consult the device’s Command Reference or the port-sharing documentation for the exact setting names and supported mode; do not substitute a guessed command or value.
- Configure the port for the sharing behavior intended for multiple readers. Keep the arrangement read-only: avoid having clients transmit commands or data back through the serial port unless the application explicitly requires that behavior.
- Apply the configuration using the device’s documented procedure. If applying the change interrupts the active RealPort connection, schedule the change so you can reconnect the known-good client afterward.
- Leave the existing RealPort COM mapping intact unless the device documentation or a measured mapping issue requires a change. Configure the second Windows server with the RealPort driver and its own appropriate COM-port mapping.
The key change is on the TS 4 serial port, not simply a second Windows client installation. Documentation references in the supplied material point to the Command Reference page 204 and the port-sharing documentation page 24; use the documentation applicable to the installed TS 4 configuration rather than relying on an assumed menu label.
Verify both Windows servers receive the same input
- Connect the first server and confirm it receives valid serial data.
- Connect the second server while the first remains connected. Confirm the second COM port opens without “Could not open COM port.”
- Compare a recognizable incoming message or sequence on both hosts. Check whether data arrives at both, not merely whether both COM ports report open.
- Disconnect one host and confirm the other continues receiving. Reconnect the disconnected host and check that sharing still works.
If both clients open but only one receives data, revisit the TS 4 sharing mode and the application’s read-only behavior. A successful COM-port open alone does not prove that the data fan-out works as intended.
Avoid fixes that do not change sharing
- Do not spend time changing COM-port numbers first when the known-good host already receives data and the second fails only after it connects. A different local COM number does not configure TS 4 port sharing.
- Do not assume that installing RealPort on more Windows servers enables multiple-client access by itself.
- Do not test with simultaneous writes from the clients. This requirement is for reading serial input; transmission can create contention or alter the connected device’s behavior.
- Do not guess at a setting name, command, or mode. Use the applicable TS 4 reference and check the actual configured port before changing it.
Frequently asked questions
What happens if two Windows servers open the same RealPort COM port?
Without the TS 4 port configured for sharing, the first server may connect while the next receives “Could not open COM port.” Configure the serial port’s sharing behavior and then test both clients concurrently.
What happens if I install RealPort on both servers?
Installing the driver on both hosts does not, by itself, enable multiple readers on the TS 4 serial port. Configure port sharing on the device as well.
What happens if both COM ports open but one server sees no data?
Check the TS 4 sharing mode and confirm that both hosts are configured as readers of the intended serial stream. Verify with a recognizable incoming message while both remain connected.
What happens if port sharing still does not work?
Stop changing settings by trial and error. Record the TS 4 port configuration, RealPort driver details, connection order, and results from the two-host test, then consult Digi’s official support channels or the applicable Command Reference.