Abstract: A selected one of a plurality of unique N-bit digital code words that corresponds to an associated signaling message is continuously transmitted until it is desired to transmit a different signaling message. Decoder logic in the receiver looks at a new group of N-signaling bits during each signaling bit interval, without reference to the start of a transmitted code word, and makes a decision during each signaling bit interval as to what signaling message was transmitted. In this manner a keep-alive signal is virtually continuously provided in the receiver. Latch circuitry repeats the previous decision from the decoder logic when the current group of N-signaling bits does not correspond to one of the unique code words or an ordered permutation thereof. In an alternate embodiment a memory circuit requires that the decoder logic repeat the same decision as to what signaling message was transmitted for P consecutive groups of N-signaling bits (i.e.

Abstract: A selected one of a plurality of unique N-bit digital code words that corresponds to an associated signaling message is continuously transmitted until it is desired to transmit a different signaling message. Decoder logic in the receiver looks at a new group of N-signaling bits during each signaling bit interval, without reference to the start of a transmitted code word, and makes a decision during each signaling bit interval as to what signaling message was transmitted. In this manner a keep-alive signal is virtually continuously provided in the receiver. Latch circuitry repeats the previous decision from the decoder logic when the current group of N-signaling bits does not correspond to one of the unique code words or an ordered permutation thereof. In an alternate embodiment a memory circuit requires that the decoder logic repeat the same decision as to what signaling message was transmitted for P consecutive groups of N-signaling bits (i.e.