Data transmission system

Abstract

The main features of the present invention reside in the fact that one or more remote groups of subordinated terminal units are serially interconnected and arranged in a closed loop which is terminated at the output and input of a master unit. Each of said groups and said master unit is connected to the transmission line via a modulator and a demodulator. In order to selectively connect a pulse equipment associated with each subordinated terminal unit, and adapted for transmission of data, with the transmission line, each of said subordinated terminal units includes a switching unit, which either connects or disconnects the associated pulse equipment from the transmission line. According to the invention, the novelty resides both in the arrangement of the network connecting the subordinated terminal units with the master pulse equipment, and the procedure for the exchange of information between the master pulse equipment and the subordinated terminal unit, and vice versa, through the closed loop, and by selectively actuating said switching unit.

What I claim is: 
     
       1. Apparatus for the transmission of data characters in pulse form from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and pulse input means of said master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   each said terminal unit including:   (a) pulse responsive means connected to said pulse input means for receiving pulses appearing at said pulse input means,   (b) decoding means distinctively responsive to pulses received by said pulse responsive means,   (c) and logic means responsive to said decoding means for normally interconnecting said pulse input and pulse output means to thereby complete the loop at said terminal unit,   (d) said logic means in response to a distinctive pattern of said pulses appearing at the associated pulse input means interrupting the loop between said pulse input and pulse output means only at a terminal unit having data to transmit and enabling the application to the associated pulse output means of stored data of arbitrary variable length as required by said terminal unit for transmission over the loop to said master unit,   (e) said logic means being effective upon the opening of said loop at the first upstream terminal unit having data to send for inhibiting the receipt at any downstream terminal unit of pulses otherwise effective to control said downstream terminal unit to transmit data.   
     
     
       2. The apparatus of claim 1 wherein each said terminal unit at the conclusion of its data transmission transmitting over said loop pulses to thereby control the downstream terminal units having data to send to serially transmit their data to said master unit. 
     
     
       3. The apparatus of claim 1 wherein said logic means in response to a first distinctive order character appearing at the associated pulse input means opens the normal said interconnection between said pulse input and pulse output means to thereby enable only the first upstream terminal unit having data to send to respond to a second distinctive order character, said logic means being responsive to said second distinctive order character at said pulse input means to enable the application to said pulse output means of the stored data.   
     
     
       4. The apparatus of claim 3 wherein said pulse responsive means comprises a shift register and wherein said logic means when rendered responsive to said second distinctive order character operatively connects said pulse output means to the output of said register to thereby cause the contents of said register to be shifted out of said register and into the register of the next downstream terminal unit in response to the appearance of pulses at said pulse input means. 
     
     
       5. The apparatus of claim 1 in which said master unit includes means for transmitting data characters over said loop in said predetermined direction to one or more selected terminal units. 
     
     
       6. Apparatus for the transmission of data characters in pulse form from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and pulse input means of said master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   each said terminal including:   (a) a pulse responsive means connected to said pulse input means for receiving pulses appearing at said pulse input means,   (b) decoding means distinctively responsive to the pulses received by said pulse responsive means,   (c) and logic means being distinctively responsive to at least one distinctive pattern of pulses detected by said decoding means which is the same for each terminal unit and appearing on said loop and effective only when said terminal unit has data to send,   (d) said logic means when so distinctively rendered responsive enabling the application to said pulse output means of data of any desired variable length as required by said terminal unit for transmission over said loop in said predetermined direction to said master unit,   (e) the first upstream terminal unit having data to send acting to inhibit the receipt at any downstream terminal unit of a pattern of pulses otherwise effective to control said downstream terminal unit to transmit data.   
     
     
       7. Apparatus for the transmission of data in pulse form a plurality of which constitute a character from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and pulse input means of said master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   a pulse responsive means connected to said pulse input means at each said terminal unit and responsive to each coded character appearing at said pulse input means,   decoding means at each terminal unit distinctively responsive to different characters received by said pulse responsive means,   logic means at each said terminal unit controlled by said decoding means and responsive to a distinctive synchronizing character transmitted from said master unit for operatively interconnecting said pulse input means to said pulse output means to thereby cause any character transmitted over said loop to be substantially simultaneously received at each terminal unit and be received by said pulse responsive means,   said logic means at said plurality of terminal units being further responsive to the reception of at least one distinctive character simultaneously at said plurality of terminal units to operatively disconnect said pulse input means from said pulse output means only at each terminal unit having data to send,   and means at said plurality of terminal units and effective only at those terminal units which responded to said distinctive character for controlling said terminal units sequentially to transmit data over said loop and via successive downstream terminal units to said master unit.   
     
     
       8. The apparatus of claim 7 which includes means controlled by said logic means and effective when the associated terminal unit has data to send and receives said first distinctive character for connecting said pulse input means to said pulse output means only through said pulse responsive means, whereby each said pulse responsive means included in a terminal unit having data to send is included in series in said loop. 
     
     
       9. Apparatus for the transmission of data in pulse form a plurality of which constitute a character from a plurality of terminal units to a master unit comprising in commbination: pulse input and puse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and input means of the master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   first means at each terminal unit responsive to a first distinctive signal appearing at the associated pulse input means only if said terminal unit has data to send for opening said loop,   second means at each terminal unit which is effective in response to a second distinctive signal applied to the associated pulse input means only at those terminal units which responded to said first signal for applying to the associated pulse output means the data stored at said terminal unit for transmission over said series loop to said master unit,   means at each said terminal unit responsive to a signal other than said second signal and received from the immediately preceding upstream station for reclosing the loop at said terminal unit.   
     
     
       10. Apparatus for the transmission of data from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and input means of the master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   and means at said plurality of terminal units, and initiated into operation in response to signals transmitted over said loop, said signals acting serially only on said means at a single terminal unit at a time and only on those terminal units having data to transmit and in the order in which they appear on said loop in said predetermined direction to interrupt said loop and to apply to said loop to said master unit for transmission over the remainder of the loop the data of arbitrary variable length stored at the respective terminal unit. .[.   
     
     
       11.  The apparatus of claim 10 in which said master unit includes means for transmitting data characters over said loop in said predetermined direction to one or more selected terminal units..]. 
     
     
       12. Apparatus for the transmission of data characters in pulse form from a plurality of remote stations to a master unit comprising in combination: at least one terminal unit included in each said remote station;   a modulator and a demodulator for each said remote station and for said master unit;   said at least one terminal unit at each said remote station being connected serially between the demodulator and the modulator for the associated station, said remote stations being serially connected to each other over a series loop extending between the modulator and demodulator of said master unit;   each said terminal unit including,   (a) a register for receiving and storing distinctive characters transmitted over said series loop both from said master unit and from any upstream remote station,   (b) decoding means distinctively responsive to the characters stored in the associated register,   (c) logic means responsive to said decoder,   (d) data storage means for storing data for selective transmission over said loop to said master unit, and,   (e) pulse input means and pulse output means,   (f) a gate connected between said pulse input and pulse output means,   said logic means being at times operable in response to distinctive pulse signals appearing on said loop and in the associated register to open said gate and thereby prevent the application of pulses to said pulse output means from said pulse input means and to connect said data storage means to said pulse output means for transmission of said data over said loop to said master unit,   said logic means being effective upon the opening of said loop at the first upstream terminal unit having data to send for inhibiting the receipt at any downstream terminal unit of an order character otherwise effective to control said downstream terminal unit to transmit data.   
     
     
       13. Apparatus for the transmission of data from a plurality of remote stations to a master unit comprising in combination: at least one terminal unit included in each said remote station;   a modulator and a demodulator for each said remote station and for said master unit;   said at least one terminal unit at each said remote station being connected serially between the demodulator and the modulator for the associated station, said remote stations being serially connected to each other over a series loop extending between the modulator and demodulator of said master unit;   each said terminal unit including,   (a) a register for receiving and storing distinctive characters transmitted over said series loop both from said master unit and from any upstream remote station,   (b) decoding means distinctively responsive to the characters stored in the associated register,   (c) logic means controlled by said decoder,   (d) data storage means for storing data for selective transmission over said loop to said master unit, and   (e) pulse input means and pulse output means,   said logic means being normally in a first condition wherein said logic means is effective to connect said pulse input means to said pulse output means,   said logic means being further operable to a second condition in response to a distinctive signal appearing in said register at a time when said data storage means is storing data for transmission to said master unit to disconnect said pulse output means from said pulse input means to thereby open said loop at each terminal unit having data to send,   said logic means when in its said second condition being additionally responsive to a particular distinctive signal appearing in said register to operatively connect said data storage means to said .[.data.]. .Iadd.pulse .Iaddend.output means only at the first upstream terminal unit which had data to send, said logic means when in its said second condition being responsive to any further signal in said register other than said particular distinctive signal to restore said logic means to its said first condition and thereby connect said .[.data.]. .Iadd.pulse .Iaddend.input means to said .[.data.]. .Iadd.pulse .Iaddend.output means at all terminal units other than said first upstream terminal unit.   
     
     
       14. The apparatus of claim 13 wherein said logic means when in its said second condition connects said pulse input means to said pulse output means only through said register. 
     
     
       15. Apparatus for the transmission of data characters in the form of pulses from a plurality of remote stations to a master unit comprising in combination: at least one terminal unit included in each said remote station;   a modulator and a demodulator for each said remote station and for said master unit;   said at least one terminal unit at each said remote station being connected serially between the demodulator and the modulator for the associated station, said remote stations being serially connected to each other over a series loop extending between the modulator and demodulator of said master unit and over which pulses originating with either said master unit or any terminal unit are transmitted always in the same predetermined direction; each said terminal unit including means normally effective to maintain said series loop closed at said terminal unit but being responsive to distinctive signals appearing on said loop to interrupt said loop and to apply to said loop pulses of any number as determined solely by said terminal unit for transmission to said master unit.   
     
     
       16. Apparatus for the transmission of data from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and pulse input means of said master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   first means at each said terminal unit responsive to a distinctive first signal appearing at the associated pulse input means only when said terminal unit has data to send for operatively disconnecting said pulse input means from said pulse output means,   second means at each said terminal unit responsive to a distinctive second signal appearing at the associated pulse input means only provided that said first means has been rendered responsive to said distinctive first signal for applying the data stored at said terminal unit to the associated pulse output means,   each said terminal unit at the termination of its transmission of data over said loop to said master unit transmitting both said distinctive first and second characters and also operatively reconnecting the associated pulse input and pulse output means,   whereby the transmission of said distinctive first and second characters by said master unit causes the transmission of data only from the first upstream station in said loop having data to send and the subsequent transmission of said distinctive first and second characters by said first upstream station causes the transmission of data only from the next station downstream of said first upstream station which had data to send, and so on, until every station in said loop which had data to send has transmitted its data in turn over said loop to said master unit.   
     
     
       17. A method of data transmission between a master unit and a plurality of remote terminal units each having a pulse input and a pulse output which are normally operatively interconnected and with said terminal units being serially connected in a loop extending from the pulse output to the pulse input of the master unit, said method comprising the steps of: transmitting from said master unit to each said terminal unit over said loop a first distinctive signal,   decoding said first signal at each terminal unit and in response thereto interrupting said loop provided only that said terminal unit has data to transmit,   transmitting from said master unit over said now interrupted loop a second distinctive signal,   decoding said second signal only at the first upstream terminal unit which had data to transmit and in response thereto applying to said loop the data stored at said terminal unit for transmission to said master unit,   transmitting again at the termination of the data transmission from said first upstream terminal unit said first and second distinctive signals.   
     
     
       18. A method of data transmission between a master unit and a plurality of terminal units each having a pulse input and a pulse output and with said terminal units being serially interconnected in a loop extending from the pulse output to the pulse input of the master unit, said method comprising the steps of: at times transmitting at least one distinctive order character over said loop from said pulse output of said master unit to initiate a cycle of data transmission from all those terminal units, one at a time, which are ready to transmit data to said master unit,   in response to said at least one distinctive order character interrupting said loop only at a terminal unit having data to send and applying to said loop at said terminal unit the stored data of arbitrary variable length for transmission to said master unit,   said transmission of data from said master unit and also from each said terminal unit always occurring in the same direction around said loop.   
     
     
       19. A method of synchronous data transmission over a loop comprising a serial transmission channel extending between the output and input of a master unit and having a plurality of terminal units each including an input and an output which are serially connected in said loop, each terminal unit being selectively operable between two distinctive conditions in a first of which its input is effectively connected to its output and in the second of which the input is not connected to the output and in response to signals appearing at the input said terminal unit is operated between its two said distinctive conditions, the transmission of data from the master unit or from any terminal unit proceeding always in the same direction over the loop, the method steps comprising: controlling each terminal unit to its said first condition in response to the receipt of a first distinctive signal at its input as monitored by the associated register,   controlling each terminal unit having data to send to its second distinctive condition in response to the reception of a second distinctive signal at its input as monitored by the associated register,   and thereafter transmitting stored data over said loop only from the first upstream terminal unit which is now in its second distinctive condition following the resetting of each downstream terminal unit which was operated to its said second distinctive condition back to its said first distinctive condition.   
     
     
       20. The method of claim 19 wherein said first upstream terminal unit at the conclusion of its data transmission transmits over the loop a further second distinctive character to thereby control all downstream terminal units having data to transmit to their second distinctive condition, and thereafter transmitting over the loop the stored data from the first downstream terminal unit of the group of terminal units which was operated to its second distinctive condition in response to said further second distinctive character while concurrently restoring to its first distinctive condition each remaining terminal unit. 
     
     
       21. Apparatus for the transmission of data from a plurality of terminal units to a master unit comprising in combination: pulse input and pulse output means for each said terminal unit and for said master unit,   a single series loop connecting said terminal units in series along said loop between the pulse output means and input means of the master unit and over which pulses originating either with said master unit or any terminal unit are transmitted always in the same predetermined direction,   control means at any one of said terminal units which is rendered effective, only when said terminal unit has data to transmit, in response to a single occurrence on said loop of distinctive signals applied to the associated pulse input means, said control means when so rendered effective opening at least at the first upstream terminal unit having data to transmit a normally closed by-pass means which when in its normally closed condition permits the retransmission from the output means of said one terminal unit of any signals appearing at its input means, and further means effective at the first upstream terminal unit with data to transmit and when its said by-pass means is open for applying to said output means the data of whatever length is then stored at said one terminal unit,   and additional means at each said terminal unit for applying to said pulse output means at the conclusion of data transmission said distinctive signals to initiate the transmission of data from the next downstream terminal unit having data to transmit,   whereby the single occurrence of a transmission of said distinctive signals from said master unit initiates a cycle of data transmission sequentially from all terminal units having data to transmit.   
     
     
       22. A method of data transmission between a master unit and a plurality of terminal units each having a pulse input and a pulse output and with said terminal units being serially interconnected in a loop extending from the pulse output to the pulse input of the master unit, said method comprising the steps of: transmitting onto said loop from said master unit distinctive signals when it is desired to initiate a cycle of data transmission from all terminal units having data to transmit,   responding to each occurrence of said distinctive signals at least at the first upstream terminal unit ready to transmit data to the master unit by opening a normally closed by-pass which is effective only when closed to repeat at the output means of said terminal unit the signals received from said loop at its input means, applying to the output means the data of whatever length is then stored at said terminal unit while said by-pass is open,   transmitting from the output means of said terminal unit at the conclusion of data transmission said distinctive signals to initiate the transmission of data from the next downstream station ready to transmit data to the master unit,   and initiating a cycle of data transmission from all terminal units having data to transmit by a single transmission from said master unit of said distinctive signals. .Iadd.   
     
     
       23.  A method for controlling the transmission of data over a common loop communications channel from a plurality of terminal units each connected to said loop comprising the steps of: transmitting on said loop a distinctive signal to initiate data transmission over said loop from those terminal units having data to send;   responding at a terminal unit on said loop which has data to send and which is responsive to said distinctive signal by interrupting said loop at said terminal unit, by placing on said loop the data at said terminal unit, and by thereafter placing on said loop at said terminal unit said distinctive signal at the termination of the transmission of the stored data for similarly effecting the transmission of data from a further terminal unit having data to send,   said transmission of said distinctive signal and of said data always occurring in the same direction around said loop. .Iaddend. .Iadd.   
     
     
       24.  The method of claim 23 in which said distinctive signal and said data on said loop comprise electrical signals. .Iaddend. .Iadd. 
     
     
       25.  A method for transmitting data from a plurality of terminal units over a unidirectional communications loop, the method comprising for each individual terminal unit of said plurality the steps of: a. transmitting data from the terminal unit over the loop in response to reception at that terminal unit, at a time when it has data to send, of an order signal propagated over the loop;   b. blocking at the terminal unit onward passage of the received order signal over the loop when the terminal unit has data to send; and   c. repropagating said order signal over the loop for onward passage from the terminal unit following each transmission of data from that terminal unit. .Iaddend. .Iadd.26. In a method of data transmission from terminal units that are connected in a communications loop, in which an order signal for initiating such transmission is transmitted on the loop to reach the terminal units sequentially, and in which each terminal unit having data to transmit sends data over the loop in response to the condition in which the order signal reaches that terminal unit over the loop, the improvement wherein the response of the terminal unit to said condition includes blocking the onward transmission of the order signal past that terminal unit in the loop, and transmitting from the terminal unit itself said order signal onward in the loop following transmission of the data from that terminal unit. .Iaddend. .Iadd.27. The method of claim 25 or claim 26 wherein said order signal is a predetermined signal combination having first and second parts and said blocking of the order signal in its onward transmission is effected by altering said second part. .Iaddend. .Iadd.28. Apparatus for transmitting data over a communications loop, said apparatus comprising a plurality of terminal means for individually propagating data and order signals over the loop, and a unidirectional signal-transmission path, said path intercoupling the terminal means serially in the loop for communicating data and order signals onward in the loop between the successive ones of the terminal means, each said terminal means comprising:   (i) first means coupled in said path, said first means being selectively operable for interrupting onward transmission in the loop from the respective terminal means of signals received from said path at that terminal means;   (ii) second means coupled to said path, said second means being conditioned only when said terminal means has data to send over the loop to provide a distinctive response upon reception from said path of a predetermined order signal;   (iii) third means for operating said first means in response to said distinctive response of said second means, to interrupt onward transmission beyond the respective terminal means of said predetermined order signal;   (iv) fourth means responsive to said distinctive response of said second means to propagate in said path for transmission onwardly in the loop from the respective terminal means, signals in accordance with said data at that means; and   (v) fifth means operative to propagate said order signal in said path for transmission onwardly in the loop from the respective terminal means following each transmission for that terminal means of the data signals. .Iaddend. .Iadd.29. Apparatus for the transmission of data over a unidirectional communications loop, said apparatus comprising a plurality of terminal units intercoupled with one another serially in said loop for inputting data to the loop, each said terminal unit comprising first means providing as part of said loop a selectively-blockable signal pathway through the respective terminal unit for signals received at that terminal unit in the loop, said first means being conditioned in the event that the respective terminal unit has data to send to respond to reception at the respective terminal unit of a predetermined order signal received at that terminal unit in the loop to block said pathway to onward transmission of said order signal, second means responsive to said order signal when the respective terminal unit has data to send for propagating in said loop from the respective terminal unit signals in accordance with the data for transmission onward from that terminal unit in the loop, and third means for propagating said order signal for transmission onward in the loop from the respective terminal unit following transmission from that terminal unit of said data signals. .Iaddend. .Iadd.30. Control apparatus for operatively connecting each of a plurality of terminal units to a loop-type unidirectional communications channel, said apparatus at each terminal unit comprising:   first means for detecting signals on said loop, said first means being rendered distinctively responsive to an order signal on said loop only in the instance when the terminal unit has data to send,   second means normally permitting the onward passage of signals on said loop but being effective to block the onward transmission of said order signal in the event that said first means has been rendered distinctively responsive as aforesaid,   third means also responsive to said order signal on said loop for transmitting signals onto said loop in accordance with said data,   and fourth means effective after the transmission of said data signals to transmit said order signal onto said loop. .Iaddend. .Iadd.31. Control apparatus for coupling data and order signals between a terminal means and a unidirectional communications loop to which a plurality of such terminal means are connected; said control apparatus comprising:   first means for providing a normally unblocked but selectively blockable signal pathway through said control appparatus for signals on said loop received at such control apparatus, said signal pathway forming a part of said loop;   second means effective when the associated terminal means has data to send to respond to the reception at such control apparatus of a predetermined order signal transmitted on the loop to operate said first means so as to block said pathway to onward transmission of said order signal;   third means also responsive to said order signal, and effective when said first means has been operated by said second means to block said pathway, to enable the propagation over said loop of signals in accordance with data inputted to the associated terminal means;   and fourth means rendered effective following each transmission of said data signals for propagating said order signal over said loop. .Iaddend. .Iadd.32. The data transmission apparatus of claim 31 wherein said predetermined order signal comprises first and second parts;   said second means being responsive to said first part of said order signal to operate said first means to block said pathway to said second part, and   said third means being rendered effective by said second part of said order signal to propagate said data signals. .Iaddend. .Iadd.33. The data transmission apparatus of claim 32 wherein said third means comprises means responsive to the condition in which said second part of said order signal is not received immediately following the reception of said first part of said order signal, to operate said first means to its normal condition to unblock said signal pathway. .Iaddend. .Iadd.34. The apparatus of claim 10 in which said master unit includes means for transmitting data characters over said loop in said predetermined direction to one or more selected terminal units. .Iaddend.