This interface is a half-duplex multi-point connection. Half-duplex means that the data exchange works in both directions, but only in one direction at a time. It also means that one can transmit and receive over the same line.
Converting the common RS 232 interface to RS 485 is not so easily done. However several devices can act as masters as well as also being receivers (slaves). In total up to 32 devices can be connected to one interface. When connecting the stations together, only a two-wire cable is necessary.
Most fieldbuses operate on this interface basis. The hardware is thus always the same, it is only the protocol that differs - this says which device is being addressed, which information is for that device and what control information is required to check that the transmission has been done correctly.
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