The 485 and 487 series RS-485 data systems from American Fibertek Inc. transmit and receive RS-485 signals over optical fiber and come in single or multimode versions for use in network-based security systems. They transmit and receive one and two signals, respectively, over a single optical fiber. The systems comprise two transceivers that form a point-to-point communications link and can be set up for either two- or four-wire operation with the flip of a switch. They include diagnostic indicators for quick visual verification of system status and, via selectable dip switches, can be biased or nonbiased and terminated or not. The assemblies are available with a variety of connectors in stand-alone units or in rack card configurations.