Not able to find information on the DO-20, DIO-20, or DM-20 IOU modules.
Unable to find documentation.
Below are documents that have information on the DM-20 IOU module, DO-20 board, and DIO-20 Eclipse board.
DO-20 -> Here.
DIO-20 Eclipse Module Datasheet -> Here.
Note: The Eclipse product line is now discontinued, but the DIO-20 is available for the DM-20. The part number is 01-9000-DIO20.