Up to now, swapping out obsolete controllers that use the ANSI x3.28 protocol has proven impractical because production systems would require modification to work with a modern Modbus RTU-compatible controller. ICS Electronics addressed that issue with its Model 2399 ANSI x3.28-to-Modbus RTU controller, which makes replacement possible without making changes to the production system. The converter, which controls RS-232 and RS-485 Modbus RTU devices, features two operating modes. In the x3.28 mode, the 2399 appears as an ANSI device; all x3.28 commands are converted into Modbus RTU packets and Modbus controller responses are returned to the host system. In the SCPI mode, the 2399 operates as an IEEE-488.2-compliant devices and accepts SCPI commands to configure the converter. The 2399 also accepts ASCII commands strings for controlling any Modbus RTU device, simplifying testing and calibration of the replacement controller. The metal-enclosed, DIN-rail- or panel-mountable unit operates from 5 to 32 V dc, or from an included 115-V ac power adapter. Two serial ports can be set as RS-232 single-ended signals or as two- or four-wire RS-485 differential signals. Command-conversion firmware currently targets a Watlow EZ-Zone controller. The command set can be expanded to accommodate different system needs, or be changed to target a different Modbus device.