The MD-21 is used for applications where equipment requires a 20 mA current loop interface: for example with cash register systems and some PLC-systems. The MD-21 converts 20 mA current loop to RS-232/V.24. The units can be used in point to point applications and also for ring connection with a maximum of 6 nodes. The converter can be switched to active as a current source or to passive, depending upon the configuration of the connected equipment. The maximum transmission rate of the MD-21 is 19 200 bit/s. The MD-21 is designed to fit on a standard 35 mm top hat DIN-rail.