A Master Card is the central card in this series of interfaces. This is already an old card originally meant to be connected to a parallel printer port. Because those ports are long gone a USB expansion card was made with four parallel printer ports (and an USB interface). On such a card four Master Cards can be connected.
To clearify what (and how) everything can be connected to a Master Card a configuration drawing has been made. For this reason I have included a description of all the available cards and cables (even if I don not use them).