| 摘要 |
A central station alarm reporting system having a remote premises unit which is polled by the central station using FSK messages and reports its alarm information in DTMF (dual tone multifrequency) messages wherein a plurality of parallel bits of information is reported by the remote premises unit using a transmission comprising two tones, one tone selected from a group of high frequencies and one tone selected from a group of low frequencies, and said central station decoding the tone transmission into its bits of information. For example, if four low frequencies and four high frequencies are used at the remote premises, then the central station provides four output lines which are capable of completely describing the sixteen combinations of four parallel bits of information which can be constructed when selecting two tones for a dual tone multifrequency transmission, one tone selectable from a group of four low frequencies and one tone selectable from a group of four high frequencies. |
