| 摘要 |
968,279. Telegraphy. STANDARD TELEPHONES & CABLES Ltd. Sept. 29, 1961 [Nov. 15, 1960], No. 39143/60. Heading H4P. In a telegraphy system; a sequence of characters, occurring at random in the text of a message to be transmitted, which is identical to part of the sequence used for the " cancel " instruction, is recognized at the transmitter and causes the signals transmitted to be modified so as to prevent unwanted mutilation of the text at the receiver. In one of the described systems the " cancel " instruction comprises the sequence KKKKLLLL, and following the transmission of the sequence KKKKLLL from the text, a true " cancel " signal is transmitted which causes the receiver to cancel the last four characters received, i.e. KLLL. The transmitter then repeats these four characters and continues transmitting from the text. In this way a simulated " cancel " signal is split up and no unwanted mutilation results. A circuit for recognizing the first seven characters of a simulated " cancel " signal is shown in Fig. 2. Gates G1.1-G15 restore trigger T1 to the " 0 " state if a transmitted character is not a K, counter 7 being stepped on for each successive K transmitted. After four successive K's have been detected counter 7 selects gates G2.1-G2.5 which cause the counter to be stepped on for each successive L transmitted. In the other system described the " cancel " signal comprises the sequence XXYY, and if the sequence XXY is detected in the text the next character is deliberately mutilated before transmission. This mutilated character is detected at the receiver or transmitter and the latter then transmits a true "cancel " signal followed by a repetition from the text, the first character of the repeated sequence being the character previously mutilated. |
