'Initialize DDE
channelNumber = Application.DDEInitiate("RSLinx", "SomeTopicName")
'Read from PLC5
readValue = DDERequest(channelNumber, "N20:1")
'Read from ControlLogix
readValue = DDERequest(channelNumber, "ControlLogixTag[1]")
'Write to PLC
Set rangeToPoke = Worksheet("Sheet1").Range("A1")
'Write to PLC5
Application.DDEPoke channelNumber, "N20:2", rangeToPoke
'Write to ControlLogix
Application.DDEPoke channelNumber, "ControlLogixTag[1]", rangeToPoke
'End DDE
Application.DDETerminate channelNumber