Further Details At a maximum speed of 115.2-kbps you can go up to 4000 feet. Must be used in pairs. RS-232 is the most common serial interface in use today. This means you can use your SHM-C in RS-232 installations-industrial applications; security systems; UNIX®, DEC2, and HP® workstation connectivity; and more. Choose our 4-Wire SHM-C Async to transmit data up to 4 miles (6.4 km). Run loopback tests simply by pressing a front-panel button. Open the flip-top lid for quick DTE/DCE selection. Transformer and optical isolation protect your data from electrical interference. NOTE: SHM-C Async Modems must be used in pairs. This model is also backwards compatible with the ME800A-R3.