1. A method for communicating coded binary data at a predetermined bit time rate between stations on a data highway of a communications system, comprising the steps of: providing, at a transmitting station from which the data originates, a baseband frequency, a frequency double said baseband and another frequency which is half of said baseband frequency; coding signals to be transmitted from said transmitting station by; keying said baseband frequency to provide one data bit signal of two cycles at said baseband frequency with a particular beginning phase in response to one state in the binary data to be communicated; keying the half baseband frequency to provide another data bit signal of one cycle at said half baseband frequency with the same beginning phase as the signal provided for said one state in response to the other state in the binary data to be communicated, supplying said double baseband frequency as a prefix to data transmission, separating said prefix and said data with a bit time off period, and following said data with a suffix consisting of a period of several bit times having a waveform different from that representing either said one or said other state; and decoding at the receiver of the station receiving said transmitted signals by sampling said signals during the same part of each quarter of said bit time so that the resulting samples during each bit time are different for the different data states and for the suffix waveform and are, in that combination, unlikely to result from the decoding of noise.