Allow Commanding OPC Items
In the Security tab, the Scope Rights expander allows defining the write access on points, and this is strictly dependent on libraries. To allow commanding an OPC item, do the following:
- Configure the property as readable/writeable: in the Scope Rights expander, locate the Property Group settings and specify W.
- Configure the write operation for the property in the object model: in the Command Configuration expander, locate the Name column and enter exactly the text
Write.
About Write access configuration
- If the OPC library configuration does not provide the write access (that is, a command with Name = Write) even though the Command groups settings are configured in Security, the write operation will fail, and the third-party OPC clients will display an error code (see Standard OPC Error Codes).
- For each property, the name of each command must be unique. This means that the Write text can be specified for one command only. In case of special configurations, see the workaround described here: Unable to Write all the Values Through OPC DA Server.
- If you do not enter the exact text into the Name column (Write with a capital letter followed by lowercase letters), the command will not be executed on the corresponding OPC item.
- The write operation never writes a value directly into an OPC item. Instead, if a property is associated with a command named Write that respects the constraints described above, the command will be executed.
