The laptop opens the DIGI serial channel as a local COM port after the Ethernet link, compatible IP addressing, discovery access, and RealPort mapping are established in that order. Seeing the unit by MAC address proves discovery reached the Ethernet interface; it does not prove that IP traffic or the virtual serial path is working. Follow the packet from the application to the assigned COM port, through the RealPort driver, across the direct Ethernet cable, and into the PortServer TS2.
What path must the serial data follow?
A QBasic routine that opens a standard COM port does not communicate directly with the Ethernet interface. It opens a Windows COM device. For a PortServer channel, that COM device must be created and owned by the RealPort driver. The driver then transports serial data to the PortServer TS2 using TCP port 771.
| Path segment | Required state | Failure symptom |
|---|---|---|
| QBasic to Windows | The program opens the COM number assigned by RealPort | COM port is missing, invalid, or already in use |
| RealPort to TCP/IP | The driver targets the PortServer IP address and can use TCP 771
|
COM port exists but cannot establish its network session |
| Laptop to Ethernet interface | Link is active and both endpoints have compatible IP settings | Discovery may show a MAC address while IP access fails |
| PortServer to serial device | Serial mode, parameters, and cable match the attached equipment | The network session opens but no useful serial data passes |
Check before proceeding: confirm that the QBasic routine uses the COM number assigned to the DIGI channel, rather than an unrelated physical or virtual COM port.
Does the direct Ethernet link work?
Layer one first. Connect the laptop Ethernet interface directly to the PortServer TS2 using the crossover cable described for the installation. Verify link indication at both ends. A discovery result containing the device MAC address is useful evidence that Ethernet frames have crossed the cable, but repeat the check after any adapter, cable, or firewall change.
Disable unused network interfaces temporarily if the discovery utility selects the wrong route. Wireless, VPN, and additional Ethernet adapters can cause a discovery request or later IP connection to leave through a different interface. Keep the direct adapter enabled and inspect its link state in the operating system.
| Observation | Meaning | Next action |
|---|---|---|
| No Ethernet link | The fault is below IP | Check cable seating, adapter state, and link indicators |
| Link present, no MAC discovery | Discovery traffic is not reaching or returning through the selected adapter | Check interface selection and local security software |
| MAC discovery present | The local Ethernet path works | Configure and test IP addressing |
Check before proceeding: refresh discovery and confirm that the displayed MAC address belongs to the directly connected PortServer TS2.
How should the laptop and PortServer be addressed?
A direct cable provides no DHCP service by itself. If the laptop is configured only as a DHCP client, it may fall back to an automatic address that is not compatible with the current PortServer address. Temporarily assign a static IPv4 address to the laptop Ethernet adapter. Select an address and subnet mask that place the laptop in the same subnet as the PortServer, while keeping the two host addresses unique.
If the PortServer IP address is unknown, use the DIGI discovery or setup utility to identify the unit by MAC address and assign the required local IP settings. Discovery and normal IP communication are separate stages: the utility can locate a local device at the Ethernet layer even when the laptop cannot yet open its IP management interface.
| Setting | Laptop | PortServer TS2 |
|---|---|---|
| Address source | Temporary static IPv4 address | Known or assigned local IPv4 address |
| Subnet | Same local subnet as the PortServer | Same local subnet as the laptop |
| Host address | Unique | Unique |
| Default gateway | Not part of the direct same-subnet path | Not part of the direct same-subnet path |
Check before proceeding: use the assigned PortServer IP address to reach its configuration interface from the directly connected laptop.
What must pass through the laptop firewall?
Local security software can allow the setup program to install while blocking discovery or the later RealPort connection. Treat these as separate flows. ADDP is used to locate DIGI units, while RealPort uses TCP port 771. A successful MAC listing proves only that the discovery exchange worked at that moment.
- Identify the active firewall or endpoint-security policy on the laptop.
- Permit the DIGI discovery utility on the direct Ethernet interface so ADDP requests and responses can pass.
- Permit the RealPort driver to establish TCP communication with the PortServer on port
771. - If diagnosis requires temporarily disabling the firewall, keep the laptop isolated on the direct cable, repeat the test, and restore protection after creating the required rules.
| Traffic | Purpose | Proof |
|---|---|---|
ADDP |
Locate and identify the unit | The expected MAC address appears in discovery |
TCP 771
|
Carry the RealPort session | The virtual COM channel opens without a network-connection error |
Check before proceeding: confirm both discovery and TCP 771 work with the firewall enabled under its final rule set.
How is the virtual COM port commissioned?
Configure the PortServer channel for RealPort when the application expects an ordinary Windows COM interface. Other available connection methods—TCP connection, Serial Tunnel, Reverse SSH, Reverse Telnet, and Autoconnect—represent different data paths and do not automatically satisfy a program that simply opens a COM number.
- Open the PortServer configuration at its assigned IP address.
- Select RealPort operation for the required serial channel.
- Install or update the RealPort mapping so it targets that PortServer IP address.
- Record the COM number assigned to the channel.
- Configure the QBasic routine to open that exact COM number.
- Close any terminal, diagnostic tool, or second application that may already own the COM port, then retry the open operation.
If the COM number does not appear in the operating system, correct the driver mapping before changing serial wiring. If the COM port appears but cannot open its remote channel, return to the IP path and TCP 771. If it opens successfully but transfers no data, move to the serial side.
Check before proceeding: verify that the mapped COM port exists, targets the intended PortServer channel, and can be opened exclusively by a test application.
How do you verify the serial side end to end?
Network commissioning ends at the PortServer Ethernet interface; useful data still depends on the serial connection. Connect the intended serial device with cabling appropriate to both endpoints. Match the serial parameters required by that device, including data rate, data format, and flow-control method. Read the required values from the serial-device documentation and the configured PortServer channel rather than inferring them from the Ethernet setup.
- Connect the serial device to the mapped PortServer channel.
- Confirm that the channel configuration matches the attached device.
- Open the assigned COM port from one application only.
- Transmit a known command or test string from the laptop.
- Observe the expected response or verify received data at the application.
- Repeat the test after restoring the final firewall policy and reconnecting any network interfaces that were disabled during diagnosis.
Check completion: the application opens the assigned COM port, RealPort establishes its TCP 771 session, and a known serial exchange succeeds in both directions.
FAQ
What happens if DIGI Discovery shows the MAC address but the IP page will not open?
Ethernet discovery is working, but the IP path is not. Assign the laptop a unique static address in the same subnet as the PortServer, then check the local firewall and interface selection.
What happens if the RealPort COM port exists but QBasic cannot open it?
Confirm that QBasic uses the assigned COM number and that no other application owns it. If the port still fails, verify the PortServer IP target and permit TCP port 771 through the laptop firewall.
What happens if the COM port opens but no serial data returns?
The Ethernet and RealPort stages may already be working. Check the selected PortServer channel, serial cable, device parameters, and flow control, then finish by sending a known string and confirming the expected bidirectional response.