Used for controlling RS-232 and RS-485 Modbus RTU devices, Model 2399 simplifies replacement of obsolete ANSI controllers with Modbus RTU-compatible controllers. Firmware handles Watlow XonXoff and ANSI X3.28 protocol, and end-user configures unit with ANSI commands used in system and equivalent registers in Modbus controller. Inserted in serial path between system computer and replacement Modbus controller, multimodal system runs without any changes to system software.