rplc

Invoke RPC methods from TwinCAT PLC using ADS.

How?

Prerequisites

A RPC server (here another PLC on same machine LocalAmsNetId, but different ADS Port 852) provides following method signature:

NOTE
The method has to have the attribute TcRpcEnable in order to be invocable via RPC,
see Beckhoff InfoSys - Attribute 'TcRpcEnable'

{attribute 'TcRpcEnable'}
METHOD Greet : T_MaxString
VAR_INPUT
	sName : T_MaxString;
END_VAR
VAR_OUTPUT
	nLen : INT;
END_VAR
VAR_IN_OUT CONSTANT
	stLibVersion : ST_LibVersion;
END_VAR

Instantiate client

fbRpc : tchaxx.FB_RPC(sAmsNetId:= tchaxx.GCL.cLocalAmsNetId, 
                      nAmsPort:= 852, 
                      sInstancePath:= 'MAIN.fbRpcServer', 
                      sSymbol:= 'Greet');

// Arguments and RetVal
sArg  : T_MaxString := _AppInfo.AppName;
nLen  : INT;
stLibVersion : ST_LibVersion;
sRetVal : T_MaxString;
stRetVal : ST_AdsStatus;

Invoke RPC method

To invoke the RPC method, simply use fluent-api to describe it, e.g.

stRetVal := fbRpc.VarInput(sArg)
                 .VarOutput(nLen)
                 .VarInOut(stLibVersion)
                 .ReturnValue(sRetVal)
                 .Invoke();

See example projects RpcServer and RpcClient or unit-tests in TESTs/FB_RPC_Tests for more examples.

NOTE
Unlike the TwinCAT ADS .NET library, this implementation does not check the datatypes of the arguments before invoking.
It only matches the total size of all arguments (inputs, var-in-out and return value).

Acknowledgments

• TcUnit
  An unit testing framework for Beckhoff's TwinCAT 3