Defines whether this I/O Block is written automatically when the Value property of its I/O Block Elements is modified. If this property is set to True, all changes are sent to the device associated to the I/O Driver. Otherwise, all modifications are ignored. I/O Block Elements do not accept values if this property is set to False, unless the AllowRead property is also set to False. Example:

Sub Button1_Click()
  'Disables block writing
  Set obj = Application.GetObject("Driver1.block1")
  obj.AllowWrite = False
End Sub