The Patton Model FOI-2591-RZ-ST provide end-to-end conversion, extension, and electrical isolation of EIA-530/RS-422 circuits. Multimode optics extends the distance to 2km, while singlemode optics extends the distance to 20km. The units are transparent to all handshaking protocols, and can accept data and clock signals up to a maximum rate of 256 kbps. A regeneration switch on the FOI-2591 enables users to toggle between synchronous applications that require send timing (ST) and asynchronous or synchronous applications that require terminal timing (TT).
They support tail circuit and null modem functions for DCE to DCE or DTE to DTE communications. An alternate interface (V.35 or RS-232) may be installed at the opposite end, allowing the user to create a fully isolated interface converter.

The units can be used in areas of high electrical noise or in and out of RF shielded enclosures. The fiber optic cable is not susceptible to interference caused by impulse noise, crosstalk, or EMI. Patton recommends “R” units for high security applications because they have added filtering and shielding for RFI suppression.

FOI version units can be mounted in several redundant powering chassis; rack and wall mount options including Tempest and NEMA alternatives.