Read tag value and write to spreedsheet

I have included a segment of code. Instead of writing a constant I would like to read an external tag and write the value to cell contents.

Sub OnClick(Byval Item)

Dim objExcelApp
Set objExcelApp = CreateObject("Excel.Application")
objExcelApp.Visible = True
objExcelApp.Workbooks.Open "C:\ExcelExample.xls"
objExcelApp.Cells(4, 3).Value 3
objExcelApp.ActiveWorkbook.Save
objExcelApp.ActiveWorkbook.Close
objExcelApp.Quit
Set objExcelApp = Nothing

End Sub

Yes, the actual question is, instead of writting a constant in the sample code, how can i use a an external tag reference?

End Sub