What do I need before connecting a Modbus TCP PLC to SCADA Desktop?

You need the PLC IP address, the Modbus TCP port, the unit ID if your device uses one, and a list of registers you want to read or write.

Does SCADA Desktop support Modbus TCP?

Yes. SCADA Desktop is designed to connect to Modbus TCP devices on the local network and display live data on dashboards.

What port does Modbus TCP usually use?

Modbus TCP commonly uses port 502, although some devices can be configured for a different port.

Can I set alarms after connecting the PLC?

Yes. After the tags are working, you can add threshold alarms, logging, and trends inside SCADA Desktop.

Why is my PLC not showing live values?

Check the IP address, port, unit ID, register address, and firewall settings. Most issues come from one of those five items.

How to Connect a Modbus TCP PLC to SCADA Desktop

July 7, 2026 · 11 min read

SCADA Desktop is built for local industrial monitoring on Windows. One of the most common setup jobs is connecting a Modbus TCP PLC, then turning those registers into live dashboards, alarms, and historian data.

This guide walks through the practical steps: find the PLC IP address, confirm port 502, create tags, and verify that the values are updating in the desktop app.

Before you start: Make sure the PLC is reachable on the same network, and keep the register map handy. Most connection issues are caused by an IP mismatch, wrong unit ID, or register address error.

Step 1 — Collect the connection details

1. Find the PLC IP address

Open the PLC network settings and note the Ethernet IP address that SCADA Desktop will use.

2. Confirm the Modbus TCP port

Most devices use 502, but some PLCs expose a custom port. Match the value in the PLC configuration.

3. Check the register map

Write down the holding registers, input registers, coils, or discrete inputs you want to monitor. The tag setup depends on the exact register address.

Step 2 — Add the device in SCADA Desktop

Open the Devices screen and create a new Modbus TCP device. Enter the IP address, port, and any required unit ID. Save the device and watch for a green polling status.

Step 3 — Create tags

For each signal, add a tag with the correct function code and address. If the PLC uses holding registers, select the right Modbus function and data type, then save the tag.

Step 4 — Build your dashboard

Once the values are coming through, add gauges, numbers, and trend widgets. Bind each widget to the tag you created and confirm the live values update on the screen.

Step 5 — Add alarms and history

After the connection is stable, create threshold alarms and enable historian logging. That lets you track when a value crosses the limit and review the trend later.

Troubleshooting

Wrong IP address: the most common cause of failed polling.
Port mismatch: confirm the PLC is listening on the same port you entered.
Register offset error: many PLCs use different address bases.
Firewall or network block: verify local network access from the Windows PC.
Wrong data type: floating point and integer tags can look broken if the type is mismatched.

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