The 3189 ISA isolated serial interface provides the PC with two Isolated RS-422, RS-485 Asynchronous links to data collection and other devices. Isolation is important in installations where the equipment connected to the PC is either located far from the host system, or on a different power transformer circuit. The optical isolation feature of the 3189 eliminates the risk of Ground Loop Current, a commonly neglected and misunderstood phenomenon which leads to data errors and the destruction of communications equipment.