MiniBus™ Digital Databus System System Operation in Boats The above schematic shows 8 rocker switches connecting to the SIM which is mounted behind the panel. The SIM connects via a twisted pair to a PDM which controls some of the functions. A second PDM controls other functions. More SIMs can be added to the system to give a second control location, which could be mounted for example in the bow or stern. Similarly, more PDMs could be added to the system. The PDMs are mounted near to the heavy equipment which they control. This means that the heavy battery cables do not need to be routed to the panel, passing through decks and bulkheads - a distinct benefit.