Data communication system

摘要

A data communication system including a central host terminal and a large number of remote terminals communicating with the host terminal through telephone lines. The remote terminal decodes frequency-shift-keyed signals and modulates an RF generator to display the data represented by the FSK signals on a conventional television screen. The remote terminal also includes a keypad and conventional two-tone signal generator for transmitting data to the host terminal. The remote terminal may also include a card reader and a frequency-shift-keyed modulator for generating FSK signals corresponding to information magnetically recorded on a card. The host terminal includes a TOUCH-TONE decoder for providing data signals indicative of the information from the remote terminals, an FSK decoder for generating data signals indicative of the information contained on cards read by the remote terminals, and an FSK modulator for transmitting FSK signals to the remote terminals. The FSK modulator in the host terminal switches from one frequency to another only at the zero crossings of the signal in order to prevent unwanted harmonics from being generated on the telephone lines. In order to allow the remote terminals to transmit alphanumeric data, a number of twelve-key keypads may be combined using circuitry which generates a keypad-identifying signal each time a key is pressed to uniquely identify the depressed key.