SYSTEM DESCRIPTION

Extends the range of digital voltages using a Frequency Shift Keying (FSK) Interface Unit. The Digital to FSK Inter face Unit allows eight discrete optically isolated digital input signals to be converted to a FSK signal which can then be sent over twisted pair copper wire over a much greater distance. It also decodes the incoming FSK signal and provides eight discrete optically isolated digital output signals capable of sinking at least 50 ma. This method of sig nal transmission is much less sensitive to interference and can be used to extend the digital signals from four feet to four miles. The Digital to FSK Interface Unit also provide LEDs to indicate the status of the input and output signals. Transmit and Receive LEDs provide an indication of FSK signal line status as well as a “Communication Good” LED and optically isolated output to indicate proper communication.