The Multiserial board also known as Machine Control

The Multiserial board or Machine Control, is a special Zorro II card that was designed for both DraCos and big box Amigas. It provides, as the name suggests multiple serial RS-232 interfaces (actually two). But unlike many similar expansions, it has the peculiarity that it contains two RS-422 interface. The RS-422 standart allows much faster baud rates than RS-232 and has the capability of covering longer distances (upto 1.5 kilometres)

(picture taken from DaMi http://draco.efektivne.eu/index_1.htm)