4 Built-in relays: Control for multiple devices, including screens and room lighting/darkening; 4 I/O ports: Flexible control for AV and auxiliary devices; Screen Mode; LAN to RS-232 breakout; Adds two additional RS-232 ports to the control system; Relay test buttons;Each relay has its own test button with LED status indication; Configuration through RS-232 or LAN; RS-232 Loop-through