Patent GB-1121915-A (GB)
Title: Data transmission system
IPC: H04L13/08
Filed: 1966-09-22
Abstract: 1,121,915. Digital data storage. INTERNATIONAL BUSINESS MACHINES CORP. 22 Sept., 1966 [4 Oct., 1965], No. 42278/66. Heading G4C. A data store, acting as a buffer between a first terminal which transmits and receives messages in serial-parallel form and a second terminal which transmits and receives messages in serial-serial form, stores each message in a code which differs from that in which it was received. A delay line loop acts as a buffer for information transfer in both directions (only one at a time) between a typewriter and a data processor. In a transmit mode, a message entered manually on the typewriter keyboard is transferred serial by character, parallel by bit to the vicinity of the delay loop to be stored serial by bit therein and from the loop serial by character, serial by bit via a transmission line to the central processor. In a receive mode, a message is transferred serial by character, serial by bit via the transmission line into the delay loop and then from flip-flops fed by the loop it goes serial by character, parallel by bit to the typewriter where it is printed out. Each 8-bit character is preceded by a " character start " 1-bit when in the delay loop during transmit mode or on the transmission line during both modes. In the delay loop each 1-bit is represented in no-pulse-pulse form, and each 0-bit in no-pulse-no-pulse form. The message or part message in the delay loop at any one time is preceded by a " start of message" mark, represented as pulse-pulse, and followed by an " end of message " mark, represented as pulse-no-pulse. In the transmit mode, each character is entered into the delay loop by locating the " end of message " mark, then overwriting it by writing in the character and inserting a new " end of message" mark immediately following. When the delay loop is full, indicated by detection of the " end of message" mark immediately preceding the " start of message " mark, or when the operator presses an " end of message " key, the stored message is transferred to the transmission line, one bit every four revolutions of the delay loop, as indicated by a binary revolution counter counting passes of the " start of message "  mark. As each bit is removed the " start of message " mark is deleted and rewritten adjacent the first of the bits remaining. Operation terminates four revolutions after the " end of message " mark is detected immediately after the " start of message " mark. In the receive mode, arrival of a " character start " 1-bit on the transmission line causes insertion into the delay loop of a " start of message " mark immediately followed by an " end of message " mark. The eight following character bits are entered into the delay loop, one per four revolutions, as indicated by the revolution counter counting passes of the " end of message" mark, each bit replacing the " end of message " mark which is then rewritten immediately following. One revolution after one character has thus been stored, it is gated into eight flip-flops to convert it to parallel form and then passed to the typewriter for printing. Three taps on the delay loop enable pulse patterns therein to be detected. A series of tapped electromagnetic delay lines is provided for some timing purposes. It is mentioned that level setting devices, code converters and modulatordemodulators may be included as desired.