The Model 8277 is a unique asynchronous fiber optic modem whose optical interface can operate in either point to point or ring (daisy chain) configurations and whose electrical interface can also operate in point to point or multi-drop configurations depending on the user selected interface. The Model 8277 electrical interface is switch selectable between RS-232, RS-422 and RS-485. Switch selection enables data to flow from the electrical interface to the optical transmitter or to be controlled by the Request To Send, RTS, line.