The TXI-48 Tally Expansion Interface provides general-purpose outputs and inputs between various pieces of equipment. In almost every Tally system, there are cameras, tape machines, or other equipment that require a control signal to indicate on-air, next-to-air, isolation, or some other useful condition. In some cases, there is signal switching equipment that, rather than having a serial port for interrogation and control, provides only parallel control signals to indicate switching activity. In either of these situations, the Ultrix – TXI-48 Tally Expansion Interface provides general-purpose outputs and inputs between this equipment. Each unit provides up to 48 inputs and 48 outputs in a single rack unit. Outputs are dry relay contact closures, and inputs can be optically isolated, voltage sensing, or pull to ground type. Users can also cascade many TXI Interface Units to extend system capacity up to 2048 inputs and 2048 outputs per TSI-4000 unit using TCP/IP or RS-422 / 485.