OPC UA

There is no server to add. Nothing is configured, no node is created in the project tree, and no port is chosen. The server is part of the runtime, and what decides whether it runs, and what is in it, is written in your PLC code.

An attribute on the variable, and nothing else

A variable is published by carrying an attribute:

{attribute 'OPC.UA.DA' := '1'}
gSpindleSpeed : REAL;

Three keys mean the same thing, and any of them will do:

OPC.UA.DA	the one to reach for
OPC.UA.EXPORT	accepted
OPC.UA.ENABLED	accepted

The key is read without regard to case, and the value is true when it is 1, true, yes or on. Anything else is false.

Marking nothing does not give you an empty server. It gives you no server

This is the part that surprises people who have come from a system where the server runs and you choose what to put in it. Here the marking is what starts it.

On start, the runtime reads the symbols your build produced and asks one question: does anything in here carry an OPC.UA. property at all? If nothing does, the server is not started, and the log says so:

OPC-UA server disabled: no OPC.UA metadata in <symbols file>

So a machine whose logic carries no attribute has no OPC UA endpoint to connect to. That is not a fault to chase on the network.

There is a second way to reach the same state. If your code carries the flags but every one of them is false, the server is off. A '0' is not “publish it as read-only”; it is “do not publish anything on my account”, and if it is the only flag in the project, the server does not come up.

What a client connects to

The endpoint is the runtime’s own, on port 4840 unless the installation was given another. The address space is the PLC: your symbols, under one node, alongside the rest of what the control publishes.

Where to go next

• PLC: where the attribute is written.
• Building & Deploying a Project: what the build produces, and how the symbols reach the target.