Data sources
Writing to OPC UA
Besides reading data, the OPC UA data source can also write values back to the server. The recommended way is the Set variable Building Block: you pick the variable you want to change and the block dynamically rebuilds itself to match that variable — including a value input that is already typed correctly.
Attention
This requires at least one previously created OPC UA data source. The Building Block writes in the context of that connection.
Find the OPC UA blocks
Open the Building Blocks editor for any script (for example a [Button] click, a Timer or a Global event) and make sure [Block Mode] is active. Use the block search (1) to filter for OPC UA. The blocks live under FUNCTIONS → Publish to external systems → OPC UA (2).
- Set variable (3): writes a value to a writable OPC UA variable node. This is the block used to push a value from the Peakboard application back to the server.
- Call method (4): calls an OPC UA method exposed by an object node on the server, without using a return value.
- Call method with return value (5): calls an OPC UA method and returns its result, so you can reuse the returned value — for example to store it in a variable.
Add the Set variable block
Double-click Set variable (or drag it onto the canvas). The block starts in a minimal state with only the connection row.
- for connection (1): the OPC UA data source the block writes to. Pick the connection from the dropdown.
- Reset / select variable (2): the refresh icon opens the node browser so you can choose which variable to write.
- As long as no variable is selected, the generated code (3) shows the hint
-- !!! Please reset the connection and select a variable !!!.
Choose the variable to write
The refresh icon opens the [Select OPC UA nodes] dialog — the same node browser used by the data source. It shows the address space of the connected server.
- Pick a writable variable (1): expand the tree and tick the checkbox of the variable you want to write. Only variable nodes whose
AccessLevelallows writing can be changed on the server. - Select (2): confirm the choice and return to the editor.
The block adapts dynamically
Once a variable is selected, the Set variable block rebuilds itself: it now exposes a target row and a typed value input.
- for connection (1): the OPC UA connection used for the write.
- write to variable (2): the node that was picked, shown with its NodeID and browse path. Use the dropdown to switch to another writable variable of the same connection.
- value (3): the value to write. Because the block knows the data type of the chosen node, this input is already typed correctly (a Number node expects a number, a Boolean node a boolean, and so on). Plug a value, a [Get value] block or any matching expression into this socket.
- Generated code (4): the block produces the matching
writevaluecall automatically, for exampleconnections.getfromid('…').writevalue('ns=2;s=TemplatesData1_Temperature', 0). The block already passes the value in the correct OPC UA data type.
Writing from a script
The same write operation is also available directly in script code, which is useful for advanced scenarios:
-- datasourcename.writevalue(NodeID, Value)
data.opcua.writevalue('ns=3;s="Data_block_2"."IntegersWords"."int1"', toint16(12))
The NodeID can be found in the “NodeID” field of the variable in the browse dialog of the OPC UA data source.
Note
The NodeID can also be created using UaExpert or a similar tool.
For the Peakboard Script Engine all numbers are equivalent. Therefore all numbers are processed as “double”. This means that these numbers cannot be stored on an OPC UA server without further ado.
Note
The Peakboard Script Engine knows only three data types: bool, number and string! Therefore, when you write from script code, a conversion according to the following table is necessary. The Set variable Building Block does this conversion for you.
The following table provides an overview of the OPC UA data types and their corresponding conversion functions:
| OPC UA Datatype | Conversion Function |
|---|---|
| byte | tobyte() |
| sbyte | tosbyte() |
| float/single | tofloat()/tosingle() |
| int16/short | toint16()/toshort() |
| int32 | toint32() |
| int64/long | toint64()/tolong() |
| uint16/ushort | touint16()/toushort() |
| uint32 | touint32() |
| uint64/ulong | touint64()/toulong() |
| datetime | todatetime() |
| guid | toguid() |
