Patent GB-936804-A (GB)
Title: Method and equipment for establishing and maintaining synchronism in duplex telegraph systems, particularly of the type-printing kind
Inventor: DUUREN HENDRIK CORNELIS ANTHON
IPC: H04L7/02
Filed: 1960-01-05
Abstract: 936,804. Printing telegraph systems. DE STAAT DER NEDERLANDEN, TEN DEZE VERTEGENWOORDIGD DOOR DE DIRECTEUR - GENERAAL DER POSTERIJEN, TELEGRAPHIE EN TELEPHONIE. Jan. 5, 1960 [Jan. 19, 1959], No. 332/60. Class 40 (3). In a two-way signalling system in which transmission of signals from each station is effected in groups of signals with at least the first signal of each group being intentionally distinguishably different from another signal or the other signals of the group, the transmission of signals from one station is initiated in response to the identification of a predetermined signal received at said one station from the other station as being such first signal of a group whereby a predetermined time relationship is established between the groups of signals transmitted by the two stations, and each station upon the interruption of the correct reception of signals is arranged to modify the transmission sequence of at least one of the two stations in such a manner that said predetermined time relation is preserved upon resumption of transmission from both stations. Diagrammatic arrangements, Figs. 1 (a), 1 (b).-A station A initiates calling by transmitting a series of 7-unit equal-ratio (e.g. 3M-4S) signals I and station B on correct reception of two of the signals in succession operates to transmit a signal I followed by three idle-time signals #. The reception of the signal I by station A causes its transmitter to send to B a similar group comprising the signal I followed by three signals # in which the polarities of the two final # signals are reversed to a 4M-3S relation. As shown in Fig. 1 (b), reception is normal until the letter C from station A has not been correctly received at station B which has printed A, B and transmitted c, d and e. The erroneous reception detected at station B controls its transmitter to initiate the sending of signals I stepping its register so that signals c, d, e are stored. At the station A, the detection of the received signal I arrests the transmitter which has sent the letter E and also the printer which has printed e and sends to the station B the signal I which is an indication that it is to repeat the signals C, D, E. At station B, the letter C is received and printed and followed by D and E, whilst its transmitter sends e, already printed at station A and not reprinted, followed by the letters f, g ... and transmission proceeds normally. A further diagrammatic representation, Fig. 1 (c) (not shown), illustrates failure of station A to receive correctly the z transmitted by station B and the ensuing operation. Diagrammatic arrangement, Fig. 2.-Prolonged and subsequent overlapping erroneous reception commences when the letter D from station A is not correctly received at station B which has printed letters A, B, C, and has transmitted a, b, c which have been printed at station A. The erroneous reception at station B causes the transmitter to send a repetition cycle of four signals I during which the storage device is stepped to set up characters a, b, c for repetition, if required. The correct reception at A of the first signal I initiates the repetition cycle I, D, E and F, but since the I signal of the group is erroneously received at B, it again transmits the repetition cycle of four I's in which the characters are again moved in the storage register for repetition, if necessary. The fourth signal I of this sequence is not correctly received at station A, and at the end of its repeat cycle, i.e. I, D, E and F, it now sends the four signals I and stores the signals D, E, F in preparation for further transmission. At the station B, a third repetition cycle of the four signals I is inaugurated, but at the second signal I when the letter a is stored for transmission, a relay STO operates to disable the storage distributer so that the character register is held at the position to transmit the letter a when message transmission is resumed. The third and fourth signals I transmitted by station A are correctly received by station B and a relay ST operates to restart the distributer. The signals from station B are still being incorrectly received at station A at the end of its cycle requesting repetition from station B, and station A sends a further sequence of signals I requesting repetition. The third and fourth of these signals are correctly received with reversed polarity by station B which has sent a signal repetition cycle Ia, Ia, Ib, Ic. The reception at B of the signals with reversed polarity indicates that they formed the second period of a group cycle, and the character storage is again operated to set up the letters b, c in their normal positions in the character register as at the end of a cycle. These signals are correctly received and are not printed, but in view of the prolonged disturbance, and as the station A was the calling station, it sends a further set of four signals I which are correctly received by the station B which again repeats its cycle I, a, b and c, also correctly received at station A, and at which the I signal causes its transmitter to repeat the signals D, E, F which are received without fault at station B and are printed. The letter d at the beginning of the subsequent transmitting cycle from the station B is correctly received at the station A and is duly printed. Transmitter circuit arrangement, Fig. 3.- For message transmission a tape transmitter PZ selectively closes contacts a1 . . . e5 connected to gates with a priming potential from output 1 of an idle-time transmitter IT, and selectively passing pulses ZP3 to a code-converter ZCV operated by a pulse ZP4, and later in response to a pulse ZP2 passing the 7-unit code to the triggers A1 ... G1 of a signal storage I. During subsequent cycles the signals are passed in sequence to storage arrays II, III and the first signal transmitted is inserted again in the array I under control of pulses ZP1A. The transmission of the coded signals from the store I is effected by pulses PVA ... PVG from the seven stages of a distributer ZVA ... ZVG stepped by pulses PV derived by frequency division from a multivibrator ZT200 operating at 200 c.p.s. For idle-time signals α or #, the trigger IT is reversed so that its output 1 blocks gates 31 ... 35 and for the α signal the gates 36, 37, 38 are open to ZP3 pulses to set marks on the triggers A1, B1, F1 of storage I, of which stages B1, C1, G1 are set for the signal # by moving a switch Sw to the right-hand position. The calling signal I is transmitted by operation of a trigger ZS1 which closes the gate 318 connected to the code-element gates 311 ... 317, and opens gates 319, 320, 321 to pulses ZVB, ZVD, ZVE from the distributer ZVA ... ZVG to provide the appropriate 3M-4S signal. The stepping and circulating pulses ZP1, ZP2, ZP3, ZP4 and ZP1A for the stores I, II, III are selectively produced by the triggers ZP1 ... ZP1A under control of a pulse PVG from the distributer, and the conditions of gates 327, 328, 326, 329-gate 327 producing pulses ZP1, ZP1A if gate 329 is open, gate 328 permitting generation of ZP2, ZP3, and also ZP4 if gate 326 is open, and gates 327 and 328 simultaneously open allowing pulses ZP1, ZP2, ZP3, and also ZP4, if gate 326 is open, and additionally ZP1A if gate 329 is open. The opening of the gates 327, 328, 329 is dependent upon the outputs at terminals HHZ1, HHZ3, HHZ4 of a counting device actuated in accord with the sequential signals of the repetition cycle. Pulses PZVA from the first stage of the distributer operate a two-stage counter ZPA, ZPB so that after two signals, trigger ZPB is reversed to close gate 322 and open gate 323 to the trigger K, thereby reversing the nature or polarity of the code elements to produce two 4M-3S signals in lieu of the normal 3M-4S signals. A gate 336 controlling the inhibition of signals from the output trigger U is under the joint control of triggers M, SL which are selectively operated in dependence on whether the transmitter is of the calling or called station. These triggers prevent transmission if the two stations call each other simultaneously, and also after a prolonged interruption of traffic, establish which was originally the calling station. Receiver circuit arrangement, Fig. 4.-The incoming signals at IN are passed via one of two gates 41, 42 selectively operated by the respective outputs of the second trigger OPB of a two-stage device OPA, OPB operating so that the gates 41, 42 are operative for the first and second pairs of the signals of a group, and that all signals fed into the register OG ... OA are, if correctly received, of the form 3M, 4S. The signal elements are stepped and registered on the triggers OA ... OG and applied to a code converter OCV which produces the corresponding 5-unit signals to be applied to a printer relay PR by pulses OP6 provided a gate 47 is not blocked by a voltage Al or Be derived from triggers Al, Be operated by the signals α, #, or the voltage from terminal 4 of a counting device HHO. The incoming spaces registered in the trigger OG allow pulses OP2 to step a counter RT, and for a correct signal this is stepped to position 4 in which a voltage at terminal 2 allows the triggers S10, Al, Be to be operated by pulses OP3 if the respective signal I, α, # has been received. If the received signal is faulty, the counter provides an output RT1 which restores S10 to normal and also operates a counting device which counts four distributer cycles controllng the four signals of a repetition cycle. In operation, counter HHO provides at terminal 1 a blocking voltage during the first signal, at terminal 3 during the second, third and fourth signals, and at terminal 4 a blocking voltage during all four signals of a repetition cycle. The output of terminal 4 closes the gate 49 associated with the printer relay PR and blocks the stage OP5 of the pulse producing arrangement OP1 ... OP6 so that th