GB1027108A - Improvements relating to data transmission systems - Google Patents

Abstract

1,027,108. Data transmission. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Jan. 28, 1965 [Feb. 10, 1964], No. 5445/64. Heading H4P. In a data transmission system in which each character is transmitted as a two (or more) frequency signal having a prefix or a suffix two (or more) frequency signal, the receiver includes means for checking, for each character, that the sequence, the time relationship, and the duration of the signals are correct. The embodiment described comprises both keyboard and tape input. In one mode of operation depression of an end of message (e.o.m.) key causes the transmission of a twofrequency prefix signal and a two-frequency data signal. The two frequencies in each character are chosen from two different groups of four frequencies. The prefix frequencies are the same for each character. The receiver checks the presence and duration of the prefix frequencies and that the data signal follows it within a certain time and lasts for a certain time. When the e.o.m. signal is found to be correct, the receiver returns an answer back signal which, if of correct duration, initiates automatic transmission from a tape reader, the characters being converted to the two frequency form and prefixed as above. The signals are receded at the receiver for recording on tape. To ensure that the messages are of the correct length, the receiver counts each character. A gating arrangement indicates whether or not a message has held the correct number of characters. Several message lengths are catered for. In modifications the prefix is replaced by a suffix, storage being provided at the receiver as a consequence. Upon reception of the answer back signal manual initiation of the tape reader may be made, or the message sent from the keyboard.