Requirements of AS-Interface At the lowest control level, sensors, ntactors, motor circuit switches, indicator lamps, pushbuttons etc. which transfer volumes of information in the bit range had to learn to communicate.

The bus systems already in existence were either over dimensioned or simply could not be used for such a task. They used cables that were either too expensive or unsuitable for a direct link to the process (e.g. fibre-optic cable,shielded and non-flexible cable), and the volumes of data transmitted were simply too high. Either the data protocols were non- deterministic or the control electronics used were much too expensive if each binary sensor was to be a bus node and in an automation network there might be any number of them. Over and above that, assembly and installation needed to be as simple as possible, without the need for any special training. The costs for each connection should be low and in keeping with the volume of data to be transferred. In short: AS-Interface had to be able to network binary sensors and actuators and link them to the higher control levels, very simply, inexpensively, and meeting industrial requirements.