Defines whether this OPC Tag must be written or not automatically when the Value, any Bits (from Bit00 to Bit31), or RawValue properties change. If this property is set to True, these modifications are sent to the device associated to the OPC Driver. Otherwise, these modifications are ignored. Default value of this property is True. Example:

Sub Button1_Click()
  ' Disables a Tag writing
  Set obj = Application.GetObject("Driver1.tag")
  obj.AllowWrite = False
End Sub