GB1278141A - Telegraph signal transmission system - Google Patents

Abstract

1278141 Digital data transmission INTERNATIONAL STANDARD ELECTRIC CORP 2 June 1970 [6 June 1969] 26629/70 Heading H4P A digital data exchange includes a store having locations for each outgoing line in which are recorded the character being or to be transmitted on that line. The outgoing lines are grouped according to common characteristics which are recorded in a control word for each group held in separate other locations of the store. The control word includes a 2-bit word indicating the number of bits per character, a 4-bit word indicating the length of a bit, a 4-bit word indicating the position within a character of the bit currently being transmitted and a 4- bit word indicating the duration of the current bit left to transmit. Each control word is read several times per bit and upon each reading the 4-bit word indicating, in terms of number of reading cycles, the length of bit left to transmit is reduced by 1 and the control word rewritten in store. Upon this 4-bit word reaching zero the next character bit has to be transmitted, so that before proceeding to the control word of the next group of lines, the line storage locations of the present group are read in turn. A set of bistables for the corresponding group of output lines which determine their state (0 or 1) are set according to the read data. The control word is updated by increasing by 1 the 4-bit word indicating the position in the character of the bit being transmitted and resetting the 4-bit word indicating the length of bit left to be transmitted. The control word is then rewritten. When in a control word the 4-bit word indicating the bit position reaches zero the whole character on that group of lines has been transmitted and a stop bit is automatically transmitted. Fresh characters are added to the line storage locations from a queue store upon transmission of the stop signal. Start and stop signals limit a message and the idling and out of service state of the line may be continuous stop or start signals.