Calling RpcMethods and accessing PLC Properties

RpcMethods can be directly called type safe on the value dynamically read by a symbolic Read-TcValue. The RpcMethod In-/ and Out-/ Parameters are automatically marshalled to/from they .NET counterparts – so that the access is easy and transparently.

Accessing the RPC Methods needs to open an ADS Session and loading the symbolic information. Here we open a new session to the local PLC.

The ‘rpcSymbol’ object now contains the Symbol of the FB instance ‘fbRcp’.

This FB has a RpcMethod ‘AddValues’ with 2 INT parameters and a Property ‘PropInt’ defined (on the PLC side).

Information about these defined symbol instance can be browsed.

PS> $rpcSymbol

InstancePath Category DataType  Size Static Persistant IG   IO
------------ -------- --------  ---- ------ ---------- --   --
MAIN.fbRpc   Struct   FB_RpcPou 1152 False  False      4040 10DEE8

Beneath Properties and Methods of the Instance base class, the ‘rpcSymbol’ contains dynamically generated access properties and methods.

PS> $rpcSymbol | Get-Member

   TypeName: TwinCAT.TypeSystem.DynamicStructInstance

…
Name                      MemberType Definition
----                      ---------- ----------
AddValues                 Dynamic    dynamic AddValues
AddValuesAsync            Dynamic    dynamic AddValuesAsync
PropInt                   Dynamic    dynamic PropInt
….

Accessing the Rpc Method metadata of the symbol:

The method can be called transparently in Powershell

The same is true for the dynamic property