Data type of the node 'system/state'

[TSY1BOX]

Hello,

I would like to read the node 'system/state' (as highlighted below) by using DL_ReadNode to access the datalayer, yet I'm not sure which data type I should declare for the variables in the PLC program in Structured Text(ST).

In the Metadata of the node I found that the readType is stated in types/systemhandler/state as below highlighted.

Yet I've tried declaring the variables as string or create an enum list containing the states, none of them worked and DL_ReadNode returned the DL_TYPE_MISMATCH error.

Does anyone have any exprience on this and can shed some light?

Thank you!

[Sgilk · Accepted solution]

Hello,

From the documentation on DL_ReadNode: "This function must only be used on simple data types! For complex types please use DL_ReadNodeValue(). To use this function correctly you need to know the type of the returned value. If you don’t know the value type, the DL_ReadNodeValue() function will provide a NodeValue-object which can be used to request the specific type."

In your case, you will need to include the CXA_AUTOMATIONCORE_FBS library to access the system state flatbuffer definitions.

Here is an example...

Declaration:

PROGRAM PLC_PRG
VAR
    Result: CXA_Datalayer.DL_RESULT;
    m_fbReadNodeValue: CXA_Datalayer.DL_ReadNodeValue;
	m_Execute : BOOL;
	m_NodeValue : DL_NodeValue;
	m_address : STRING;
	fbs_system_state: common_systemhandler_fbs_CurrentState;
	get_system_state: common_systemhandler_fbs_State;
END_VAR

Implementation:

m_address := 'system/state';
m_Execute := TRUE; 
m_fbReadNodeValue(Execute:= m_Execute, NodeName:= m_address, NodeValue:= m_NodeValue);
IF m_fbReadNodeValue.Done = TRUE THEN
	  get_system_state.getRootAsState(m_NodeValue.GetData(), m_NodeValue.GetSize());
	  fbs_system_state := get_system_state.getState();
END_IF
IF (m_fbReadNodeValue.Done = TRUE) OR (m_fbReadNodeValue.Error = TRUE) THEN
    m_Execute := FALSE;
    m_fbReadNodeValue(Execute:= m_Execute, NodeName:= m_address, NodeValue:= m_NodeValue);
END_IF

See DL-ReadNode-DL-ReadNodeValue-in-CoDeSys for additional discussion on this topic.

[TSY1BOX]

Hello @Sgilk,

Thank you so much for the explicit answer and the example, it works!