IL31163A - A data transmission system - Google Patents

Description

31163/2 o»a ma mayfi*? asiya A data transmission system SVENSKA HANDELSBANKEN 0: -29368 GZ A method and an arrangement for transmitting information in a data transmission system.

The present invention relates to a method and an arrangement in a data transmission system for transmitting order-characters, address- characters and information-characters between a master unit and one or several remote groups of subordinated terminal units locally disposed, each of said groups and said master unit including a modulator and a demodulator, so called "modem''' , adapting pulses from the master unit and the subordinated terminal units to the transmission characteristics of the transmission lines, which connect said master unit and said subordinated terminal units to each other.

To interconnect an equipment built up of pulse circuits with another such equipment over a relatively long distance, it is necessary to convert the pulses into signals which are adapted to the frequency characteristics of the transmission lines. For this purpose, it is common practice to employ at one end of the line a modulator for converting a pulse into either a phase shift or a frequency shift relative to a reference signal and to connect the other end of the line to a demodulator detecting this phase or frequency shift and producing a pulse in correspondence thereto „ In systems where a plurality of pulse equipments disposed at geographically remote places are to be connected to a master pulse equipment, it is common practice to connect these remote pulse equipments and their associated modulator/demodulator units in parallel to one single transmission line for the purpose of shortening the overall length of the transmission lines required. Further, it is common practice to concentrate all pulse equipments locally disposed to one single modulator/demodulator unit by means of a traffic concentrator which, in addition to its concentrating function, effects the control functions required for the above mentioned parallel connection. This equipment, which effects the interconnection between a plurality of pulse equipments and one single modulator/demodulator unit and enables the connection of a plurality of such units of pulse equipments in parallel to one single transmission line, tends to become rather complicated.

A further disadvantage of connecting a plurality of such units in parallel to one single transmission line resides in that the most efficient mode of transmission, i.e. so called synchronous transmission, cannot be utilized, due to the fact that one demodulator will have to receive signals in alternating order from a plurality of modulators.

A further drawback of the above-mentioned parallel connection resides in that a great number of signals are required for maintaining the order of succession between the units connected to the line, and such sequence signals will intrude upon the time available for the transmission of information.

The object of the present invention is to provide a system connected to one modulator/demodulator unit, and several modulator/ demodulator units disposed at geographically distant places to be connected to one single transmission line without using any complicated equipments herefor and without involving the drawbacks of a conventional parallel system as indicated hereinbefore,; but maintaining the advantage's with the parallel system.

This object of the invention is substantially realized by the fact that the transmission lines connecting the master unit with the modems and subordinated terminal units included in the system are arranged in a closed loop in which modulators, demodulators and subordinated terminal units are serially interconnected. All signals comprising order-characters, address-characters and information-characters are transmitted in the closed loop which is arranged such that the output from the modulator of the master unit is connected to the input of the first demodulator appearing in the loop and which is associated with a first group of subordinated terminal units, serially connected with each other and forming a closed loop between the output of said first demodulator and the input of the associated first modulator, the output of which may be connected to the1 input of a succeeding second demodulator in the series circuit which is associated with a second grouO of subordinated terminal units and so on, until finally, the last modulator occurring in the loop being connected with its output to the input of the demodulator in the master unit, thereby closing the loop.

According to the invention all modulators, demodulators and subordinated terminal units are serially interconnected between the data output and data input of the master pulse equipment which transmits a stream of synchronization characters between which · subordinated terminal unit, which has information to send to the master pulse equipment and receives order-characters from said master pulse equipment, interrupts the series circuit and transmits the information to the data input of the master pulse equipment via succeeding modulators, demodulators and subordinated terminal units. The transmission ends with order-characters which cause the succeeding subordinated terminal unit with information to send, to interrupt the series circuit and send the information to the data input of the master pulse equipment, ending the transmission with order-characters and so on, until the last subordinated terminal unit with information to send has emitted order-characters which are received by the master pulse equipment, which thereby records that all subordinated terminal units have sent their information. Information from the master pulse equipment to a particular subordinated terminal unit includes address-characters The invention will now be described more in detail with reference to the accompanying drawings, in which? Fig. 1 shows a block diagram illustrating the closed loop of the data transmission system according to the invention; Fig. 2 shows a functional diagram illustrating the function of the switching unit in the transmission system according to Fig. 1? Fig. 3 shows a detailed block diagram of the switching unit.0 Fig. shows an alternative embodiment of the switching unit According to the invention, a plurality of remotely disposed groups of pulse equipments 5? 7, 9? 11 are interconnected and connected to a master pulse equipment 1 via modulator/demodulator units 2a, 2b, 13a, 13b, 1^-a, I'+b, 15a, 15b, 16a, 16b and transmission lines 12. These modulator/demodulator units operate in a manner such that the modulators 2a 1 b lLt-b 1 and 16b accept pulses at the same rate as pulses are transmitted from the output of the associated demodulators 2b , 13a , l*+a, 1 a and 16a , respectively.

The system is arranged so that modulator 2a of the master pulse equipment 1 is connected to demodulator 13a via a portion of line 12. The pulse output of demodulator 13a is connected to the pulse input of modulator 13b via a number of switching units 3 Each switching unit 3 is connected to a pulse equipment which is to be connected to the master, pulse equipment 1. Each pulse equipment 5 and corresponding switching unit 3 form a subordinated terminal unit *+. Modulator 13b is connected to demodulator l-'+a, associated with the succeeding group of subordinated terminal units, via another portion of line 12. Demodulator Ika. is connected to modulator l^t-b via switching units 3 each of which is connected to a pulse equipment 7 which together form a subordinated terminal unit 6. The system can include an arbitrary number of groups of subordinated terminal units. In the embodiment shown in Fig. 1 the system is terminated at the modulator 16b , which is connected to demodulator 2b at the master pulse equipment. The system according to the invention is not restricted, to the number of modulator/ demodulator units and switching units 3 as specifically shown in Fig. 1, but is operable with an arbitrary number of both modulator/ demodulator units and switching units.

The function of the switching unit 3 is in principle illustrated in Fig. 2, where it is: shown operating as a three-way switch, including switching means 27, a short-circuit line, a pulse register 17 and a decoding unit 18. In position 19 the switch is short-circuited. In position 20 the output of the switch 3 is connected to the input through a pulse register 17 having a capacity called a character. In the third position 21, the output of the switch 3 is connected directly to the associated pulse equipment 5, 75 9 or 11. To the pulse register 17, which is permanently connected to the input of the switch unit is :also connected a decoding unit 18 which identifies certain characters in the pulse register 17. The manner in which switching unit 3 affects the function of the system according to the invention is as follows; The system possesses three states of operation, ie. an idle state, a second state in which information can be transmitted from pulse equipments , 7, 9, 11 t the master pulse equipment 1, and, finally, a third state in which, information can be transmitted from the master pulse equipment 1 to pulse equipments , 7, 9 and 11.

In said idle state the switching units are all short-circuited and the master pulse equipment 1 transmits a continuous flow of characters, each character comprising a pulse combination A.

Since all the switching units 3 are short-circuited, the pulse output of each demodulator is connected directly to the pulse input of the associated modulator, and the flow of characters transmitted by pulse equipment 1 will be regenerated in each modulator/demodulator unit and finally return to the pulse equipment 1 through the demodulator 2b. This flow of characters has two purposes, viz. to establish synchronism between the oscillator of a demodulator and the oscillator of the preceding modulator, such as, for example, between demodulator l*+a and modulator 13b,° to establish synchronism between the pulses transmitted as a character by pulse equipment 1, and the pulses detected as a character by pulse register 17. When the characters received by combination as the characters transmitted from pulse equipment 1, the entire system has become synchronized.

Another method of synchronizing a demodulator with the preceding modulator resides in maintaining a two-way connection between them, i.e. ; to each demodulator is an auxiliary modulator connected, which transmits pulses to an auxiliary demodulator which is connected to the preceding modulator in the system. By this method signaling will indicate whether synchronism is being maintained separately between each modulator/demodulator connection.

When the master pulse equipment 1 is ready to receive information from pulse equipments 5? 75 9, 11, pulse equipment 1 will interrupt the flow of A-characters and transmit two characters, B and C, and then recommence its transmission of A-characters. The purpose of said B-and C~characters is the following; When a B-character has been identified in the pulse register 17 by decoding unit 18, the following procedure will be initiated if the associated pulse equipment 55 75 9? 11 has information to transmit; 1) The switching means 27 is set to position 20. 2) The next succeeding character stored in pulse register 17 is checked in order to establish, if said character is a C-character. 3) If the character is a C-character, the switching means 27 is set to position 21, thereby permitting only the characters transmitted from the associated pulse equipment to pass. The character C will thus be prevented from advancing to next succeedin, terminal unit in the series circuit. As a consequence, no succeeding pulse register 17 will receive character C directly after having received character B. This will cause the associated switching means 27 to be reset to the idle position. If the terminal, unit has no information to transmit when the B-cbaracter is detected in sition. The information traranitted from each of the pulse equipments ? 7, 9 or 11 will pass through the succeeding switching units in the series circuit to the input of the master pulse equipment 1„ Each transmitting pulse equipment 5? 7, 9 or 11 will. end its transmission with the characters B and C and will then reset switching means 27 to the idle position, whereby the sequence of procedures described above will be repeated in the succeeding terminal units in turn.

When characters B and C are received in the master pulse equipment 1, all pulse equipments 5? 7, 9, 11 in the closed loop have had an opportunity to transmit information, and pulse equipment 1 will respond by transmitting a character, D, indicating that the information transmitted from the subordinated terminal units has been properly received. However, if the information received by pulse equipment 1 contained errors, characters B and C will be transmitted once more, and the procedure just described will be repeated. Thus, pulse equipments 5? 7, 9, 11 which have transmitted information but received no D-character will retransmit their information.

Transmission of information from the master pulse equipment 1 to any of the pulse equipments 5? 7, 9, 13 is performed by transmitting two characters D and. X before each message. Character D indicates that the next succeeding character X, contains the address to the specific pulse equipment for which, the message is meant. Thi message will pass through all; switching units 3? bu only the pulse equipment assigned number X will respond to the information.

The switching unit 3 according to the invention has as its main purpose to enable the series connection between the terminal units and the master pulse equipment.

The unit shown in Fi . com rises three AND- ates 22 thereto a decoding unit 18 and a pulse equipment ? 7, 9, 11. In the idle position . of the switching unit 3? the input 33 and output 3>+ are short-circuited through the open AND-gate 22 and the OR- gate 2 . In the idle state, synchronism is maintained by the decoding unit 18 via a pulse register 17, being operative to decode information appearing at the input 33 of the switching unit 3 via line 35.

When the decoding unit 18 identifies a B-character in the pulse register 17, it emits a signal via lines 36 to the control logic 26 to close AND-gate 22 Via line 37. The pre-requisite is, however, that pulse equipment » 7, 9, 11 has informed control logic 26 via line 38, that it has information to transmit. At the same time, the control logic 26 opens AND-gate 23, whereby pulse register 17 is connected to the output 3^ of the switching unit 3 through AND-gate 23 and OR-gate 25, corresponding to the second state of the switching unit. If the next-following character received in the pulse register 17 and decoded by decoding unit 18 is a C-character, control logic 26 will close AND-gate 23 and open AND-gate 2 via line 31. At the same time, control logic 26 will emit a pulse to pulse equipment 5? 7, 9, 11 via line kl informing the latter that it may transmit information on line 29, which now connects output 3*+ of the switching unit 3 with the pulse equipment via AND-gate 2k and OR-gate 2 - This corresponds to the third state of the switching unit. The transmission ends with a signal from pulse equipment 5 ■> 7, 9, 11 to the control logic 26 via line 38 informing same of the fact that all information has been transmitted. Control logic 26 then closes AND-gate 23 and opens AND-gate 22, whereupon the switching unit has been reset to its idle state.

When the switchin unit is in the idle state and de informing that the information to follow is meant for a specific pulse equipment 5 or 7 or 9 or 11, then decoder 18 will transmit a signal to control logic 26 via lines 6· Control logic 26 then informs the pulse equipment via line 41, whereupon the information is received via line 3 · When the decoder has detected a character in the pulse register 17 signifying the end of the message the pulse equipment is informed by control logic 26. The switches 28a, 28b are meant for shunting of the switching unit 3 and the ulse equipment, for instance in case of break-down or absence of primary power. These switches may consist of a relay taking the positions 42a, 42b, respectively in case of absence of primary power or being controlled by a logic circuit actuating both switches 28a and 28b, According to an alternative embodiment of the invention shown in Figure 4 the third switching state of the switching unit can be taken without changing the condition of the AND-gate 23 and OR-gate 25. Lines 29 and 31 of Figure 3 are replaced by parallel lines 30 in Figure 4 between the pulse equipment 5, 7, 9, 11 on one hand, and pulse register 17 and decoder 18 on the other. Thus, if the character received in the pulse register 17 and decoded by decoding unit 18 is a C-character, the control logic 26 will inform the pulse equipment that it may transmit information on lines 30 via pulse register 17, which is connected with the output 34 of the switching unit via line 39, AND-gate 23 and OR-gate 25. Thus, in this case the condition of the AKD-and OR-gates will not be changed i.e., they will remain in the same condition as was taken in the second switching state of the switching unit.

Information transmitted from the master pulse equipment 1 t a specific pulse equipment 5 or 7 or 9 or 11 is received in said lines 30· Which of these two embodiments of the switching unit is 11 preferred depends on whether the pulse equipment is arranged to receive and transmit the bits which constitute a character in serial or parallel.

The rate of all information transmitted and received is preferably determined by a clock included in the demodulator and adapted to control the components of the terminal units > , 6, 8, 19 via line Li-3» If required, the clock signal can be amplified at the in- and outputs of each terminal unit by means of amplifiers U a. and +b, respectively.

The terminal units 6, 8, 10 forming part of a transmission system of the kind here referred to, include, for example data terminals or computers or any other equipment operating with pulses. In its most extreme form, the data transmission system according to the invention may include only one subordinated terminal unit interconnected with the master pulse equipment via modulator/demodulator units.

Claims (3)

1. 31163/2 ίf ' CLAIMS ^ 1, A data transmission system including a master unit and a plurality of remote stations each of said remote stations including at least one terminal unit, said master unit and each of said remote sta idhs having a modulator and a demodulator to adapt data to be transmitted to the characteristics of transmission lines interconnect ting said master unit and said remote stations, said at least one terminal unit being serially connected between the demodulator and the modulator of each remote station, said remote stations being serially connected to the master unit through said transmission lines to thereby form a series loop between the data-output and c&a-lnput of said master unit, characterized in that each term- > ina! unit comprises input and output means, a switching unit* a pulse register, a pulse decoder and data transmitting and receiving means, said switching means being capable of interrupting said series loop and connecting said data transmitting means to said output means, dependent on signals received in said pulse register and decoded in said pulse decoder.

2. The system of claim 1, wherein said switching unit being capable of three different states,, a first state connecting sad input means to said output means, a second state connecting said output means through said pulse register to said input means and a. third state connecting said put means to said data transmitting means.

3. The system of claim 1, wherein said data receiving means is capable of receiving messages preceded by a specific character of characters, received in said pulse register and detected by said pulse decoder. 3U63/2 * plurality of remote stations including at least one term-lhal unit, said master unit and .each of said remote stations having a modulator and a demodulator to adapt data to be transmitted to the clmraoteristic's of transmissions lines interconnecting said master unit and said remote stations, said modulator, demodulators and terminal units being ser^ lally connected through said transmission lines to thereby form a series loop between the data output and data input of said master unit, characterized iniMi that the data transmission in said series loop always occurs in one end the same direction, said transmission including order characters being transmitted through the series loop successively to each of said erminal units having information to send, each of said terminal units with information to send and receiving said order characters interrupting said series loop by cutting a normally closed by-pass in said terminal unit and connecting said data transmitting means to the series loop, said means thereafter transmitting data to the master unit in the series loop and via succeeding by-passed terminal units. , 5. The method of claim 4, wherein the master unit transmits synchronizing characters, order characters and message characters, receiving said order characters at the first terminal unit with data to transmit and interrupting said series loop, transmitting from said first terminal unit said data and concluding said transmission with said order characters, receiving said order characters at a succeeding tei^iinal unit with data to transmit and interrupting the series loop,: transmitting said data and concluding said transmissio with said, orderrCharacters, concluding a cycle when said order characters are received vat said master unit, and transmitting message characters with an address identifying an individual terminal 6, The method of claim 5# in which said order characters comprise two characters, said interruption occurring after receipt of said first character and transmission occurring after receipt of said second character. 7. The method of claim 6 in which said interruption is reset if said second character does not immediately follow said third character. For the Applicants DR. INHOLD CQHH AHD PARTNERS