Yes, you have to use DDE poking to control the process from Excel. This is if you are wanting to write data to the PLC. If you are wanting to retrieve it you can do much the same, but source and range being the PLC and target being the worksheet. Identify your Dim's (Source, Target, Channel, Item, Range).
So.. to write
Sub XXXXXX()
Dim Source As Range
Dim Target As Range
Dim DDEChannel as Long
Dim DDEItem as String
Dim RangeToPoke as Range
DDEChannel = Application.DDEInitiate(app:="RSLINX", topic:="XXX")
DDEItem = "Tag name,L1,C1"
Set RangeToPoke = Worksheets("SheetX") .Range("CELL")
Application.DDEPoke DDEChannel, DDEItem, RangeToPoke
Application.DDETerminate DDEChannel
End Sub
Don't forget to set your target.
To read
Sub XXXXXX()
Dim DDEChannel As Long
Dim ItemName As String
Dim Result As Variant
DDEChannel = Application.DDEInitiate("ServerAppName", "ServerTopic")
ItemName = "tagname,L1,C1"
Result = Application.DDERequest(DDEChannel, ItemName)
Application.DDETerminate DDEChannel
End Sub