Patent GB-1211506-A (GB)
Title: Data transmission system
Inventor: KLOSE ULRICH KONRAD
IPC: H04L12/40
Filed: 1969-03-31
Abstract: 1,211,506. Electric signalling systems. INTERNATIONAL BUSINESS MACHINES CORP. 31 March, 1969 [30 March, 1968], No. 16655/69. Heading G4H. A data transmission system comprises a receiver Z, Fig. 2, a plurality of terminal units, Fig. 1, arranged in a series along a data channel, means in each terminal unit for providing a request signal to indicate that the terminal unit has data to transmit, means in the receiver responsive to a request signal to generate an answer signal indicating that the receiver is ready to receive data, a first preparation system in each terminal unit responsive to the answer signal to initially prepare a requesting terminal unit for transmission of data, means in the receiver to generate an invitation signal to be received by the initially prepared requesting terminal unit located nearest the receiver, a second preparation system in each terminal unit responsive to the receipt of an invitation signal to finally prepare the terminal unit for transmission of data and a control signal generator at the receiver controlling the transmission of data from the finally prepared terminal unit only. When a terminal unit has data to transmit a request key T, Fig. 1, is operated to pick request relay 1 which holds over contact 1-1. Lamp L is switched on by contacts 1-2 and a signal applied to request line R. When the receiver Z, Fig. 2, is ready to receive data it sends out an answering signal A which energizes the answering relay 2 via contact 1-3 of relay 1. Relay 2 holds over contact 2-4: and relay 1 drops out. Lamp L lights now over contact 2-4 and contacts 2-1 cut off terminal units further away from the receiver. The invitation signal F generated at the receiver passes via diode D2 contacts 2-2 to pick relays 3 and 4 via contacts 2-3. Contacts 2-1 are serially connected along the invitation line F. Only the requesting terminal unit nearest the receiver will therefore respond to the signal F. Relay contact 4-1 de-energizes answering relay 2 which does not drop out immediately being held briefly in by the pulse on the first scanning line S1 via diode D4 which coincides with the signal F. After this pulse relay drops out, contacts 2-3 placing resistor R1 in series with relays 3 and 4 to enable them to make a rapid drop out at the end of tranmission. After the pulse on scanning line S1 pulses are delivered successively on each of the further scanning lines S2-Sn, one for each reading out the characters in turn from the terminal unit store IE. The output leads of the store are connected to the parallel leads I1-I8 and IP by contacts 3-1 to 3-5. At the end of a cycle relays are reset by a further pulse on scanning line S1. At the receiver the relay Z2, Fig. 2, picks over a series circuit including line F, the contacts 2-1 in all the terminal units and diode DZ3. Relay Z2 holds over contacts Z21 and rest contacts Z1-2. A request signal R from a terminal unit passes via contacts Z2-4 and Z1-3 to INTERN 1 i.e. an internal circuit not described for testing whether the receiver is ready to receive data. If it is, relay Z1 is energized so that relay Z2 drops out and relay Z3 picks. Series relay 24 does not pick at this time being shunted by contacts Z4-1. Contacts Z31 cause relay Z5 to pick through contacts Z2-2 (still closed) and close hold contacts Z5-1 which also apply a signal to the answer line A indicating readiness to receive data. Relay Z1 is now repeatedly operated by the INTERN 2 circuit. The first operation of relay Z1 opens contact Z1-1 to operate relay Z4. Contacts Z4-1 close to drop out relay Z3. Relays Z3 and Z4 respond alternately to successive operations of relay Z1. This continues until relay 22 is re-energized at the end of transmission. The cycles of relays Z3 and Z4  control the successive energization of scanning control lines S1-Sw through chain-connected relays A1-Aw. Two extra control lines (shown dashed in Fig. 1) may be provided for activating all the terminal units in turn. A priority line (shown in double dashes) allows one terminal unit to be activated before the end of transmission from another terminal unit.