FR2462067A1 - Interface for digital data transmission system - comprises three opto-electronic couplers linking data terminal to incoming and outgoing lines - Google Patents

Abstract

The interface consists of three optoelectronic couplers connected between the data terminal (71) with which they are associated and to the two lines leading to the preceeding data terminal (73) in the network and to the next data terminal (74). Each coupler comprises an LED and a phototransistor. The LEDs of the first (77/80) and third (79) couplers are in series and connected to the terminal's outputs. The phototransistor of the second coupler (78) is connected to the terminal's inputs and its LED is between +5V dc and theincoming line. The first coupler's phototransistor is connected across the two outgoing lines.

Description

The present invention relates to a data transfer interface circuit, and more particularly, to a serial digital data interface circuit which is suitable for distributing digital data from a microprocessor or a central station to any number of remote stations or as well as from a remote station to another remote station or to the microprocessor.

The technology of digital computers, the digital control of machines and processes, the techniques of integrated circuits, of advanced integration and the development of microcircuits have combined to produce a revolution in the field of manufacturing as well as inputting and distribution of production information. Operations performed at a stage may depend on the specific conditions under which the previous operation was performed. The production data necessary for a machine which performs a manufacturing phase can be stored in a central memory unit. There is therefore a need for a constant circulation of data along a production line, data which must be produced, routed, verified and received in a complex set.

 The condition that any station is capable of receiving data from, or transferring data from, any of the other stations in the set is of great importance.

A solution which requires direct bilateral interconnection between each of the stations becomes impractical when the number of these stations is large. This solution has often been abandoned in favor of a single data line along which the various stations are connected in series. A message is then preceded by an address code which identifies the extension or extensions to which this message is addressed. The data is received and stored successively by each station. If the station is not the one to which the data is addressed, this data is retransmitted to the next station, downstream. On the other hand, if the data is received by an addressed post, it is kept as well as retransmitted. This arrangement has two drawbacks. First of all, since the data is transmitted successively from one station to another, each of them must operate in such a way that the data is received by the downstream station. Then, a station cannot transmit upstream, without additional circuit, that is to say that it cannot transmit data towards a station from which it receives information.

 Optical shots comprising light emitting diodes have proven to be an extremely practical means of transmitting digital data, and an example of a transmission system employing them is described in US Patent No. 3,970,784. This patent describes digital data transmission stations capable of receiving and transmitting and connected by a single bidirectional line of data. It is however clear that if this provision is to be applied to a large number of stations, it is necessary to use a separate pair of data lines to interconnect each station with all the others.

 The invention therefore relates to a serial digital data and information interface circuit which eliminates the drawbacks of prior circuits. This interface circuit includes a series chain of optical couplers or optical isolation devices operating at the input and output of each data transmission station. Each optical coupler consists of a light source, for example a light-emitting diode, optically coupled with a controlled element sensitive to light, for example a phototransistor or a light-dependent resistor. The light-emitting diodes of two optical couplers are connected in series with the controlled element (ie the phototransistor) of the third coupler, at the output terminals of a DC power source.

 When a station receives data, the serial controlled element of the interface circuit is intermittently short-circuited by serial data pulses from an upstream transmitter station. A current can then flow in the two light-emitting diodes of the interface circuit, producing light. The first light emitting diode drives an optically coupled controlled element which transmits the data to a next station or downstream.

The second light emitting diode excites an optically coupled controlled element which supplies the data to the neighboring station.

The assembly can be extended almost without limit and can also be presented in a closed loop in which the last station on the line retransmits the data to the departure station.

 On transmission, the light emitting diode of the optical coupler, which is short-circuited by the upstream station when it transmits data, is excited by the pulses of digital data in series coming from the output of the neighboring station. A current then flows in the controlled element, such as a phototransistor, and in the light-emitting diodes of the two other optical couplers of the interface circuit.

Not only are serial data pulses sent to the next station, but also the sending station can verify the transmission using the output signal from the optical coupler used to receive the data pulses.

In a closed loop system, any data station can transmit to any other. The interface circuit is modified to avoid transmission by an interface circuit while the associated station transmits.

The object of the invention is therefore to produce a data interface circuit intended for stations for receiving and transmitting digital data in series.

 Another object of the invention is to provide a digital data interface circuit which eliminates the storage and retransmission of data in a station to which the data is not addressed.

 Yet another object of the invention is to provide a data interface circuit capable of operating in a closed loop.

Yet another object of the invention is to provide a digital data interface circuit in series in which each data station can receive and transmit data from each of the other stations on a single pair of data lines.

Yet another object of the invention is to provide a digital data interface circuit in which each transmitting station is immediately capable of reading and verifying the data coming from the data lines on which it is transmitting.

 Other characteristics and advantages of the invention will emerge during the description which follows.

In the accompanying drawings, given solely by way of non-limiting examples
FIG. 1 is a diagram of an assembly for transmitting digital information, according to the invention,
FIG. 2 represents an assembly for transmitting digital information in a closed loop comprising interface circuits of another embodiment according to the invention, and
FIG. 3 is a diagram of the modified interface circuits of the closed loop assembly of FIG. 2.

 FIG. 1 therefore represents a set of transmission of digital information to which the invention applies, and generally designated by the reference 10. A microprocessor 12 produces pulses of digital data in series on a pair of data lines 14. The microprocessor 12 can be of almost any size and has the desired amount of memory, compute and software. The microprocessor 12 is shown here simply as a representative source of digital information and should not be considered as part of the invention, nor as a limitation. The digital information pulses coming from the microprocessor 12 are passive, that is to say that no voltage is applied to the line 14 by the microprocessor 12. The signal or state "0" on the data line 14 is represented by a open circuit by the microprocessor 12 and the signal "1" or high level is represented by a short circuit of the data lines 14 established by the microprocessor 12.

 The output of the microprocessor 12 on the data lines 14 is connected to an interface circuit 21 of a first data station 22. The lines 14 are connected in the interface circuit 21 so as to short-circuit a controlled element , namely a light-dependent resistor or a phototransistor 18 forming part of a first optical coupler 16. The first optical coupler 16 also comprises a light source, generally a light-emitting diode 20 communicating optically with the phototransistor 18.

The light-emitting diode 20 is connected to the data output of the first data station 22, the operation of which will be described later. The phototransistor 18 of the optical coupler 16 is connected in series with a light-emitting diode 26 of a second optical coupler 24 and another light-emitting diode 32 of a third optical coupler 30.

 The light-emitting diodes 26 and 32 and the phototransistor 18 are connected in series with a current limiting resistor 36, at the output terminals of a low voltage direct current power source, not shown, which generally delivers a nominal voltage. of 5 volts.

 The optical coupler 24 includes a light-dependent resistor or a phototransistor 28 optically coupled with the light emitting diode 26. Finally, the optical coupler 30 includes a light dependent resistor or a phototransistor 34 optically coupled with the light emitting diode 32. The signal The output of the phototransistor 34 is applied on a pair of data lines 38 to an interface circuit 41 at a second data station 40 remote from the first data station 22.

The interface circuit 41 of the data station 40 is identical to the interface circuit 21 and comprises three optical couplers 42, 44 and 46 which are connected in the manner already described with respect to the interface circuit 21.

 The operation of the data interface circuit is obvious. The microprocessor 12 produces data pulses on the lines 14 by opening and short-circuiting them alternately, as explained above. The intermittent short-circuit of the phototransistor 18, whose impedance is normally high, lowers the resistance of the series circuit comprising the resistor 36, the light-emitting diodes 26 and 32 and the phototransistor 18, thereby circulating a current coming from the source of power supply in the light-emitting diodes 26 and 32 and the resistor 36. The light emitted by the excited light-emitting diodes 26 and 32 produces a reduction in resistance or a signal at the output of the phototransistors 28 and 34. The phototransistor 28 therefore provides the first data station 22 the data pulses transmitted by the microprocessor 12. In a similar manner, the phototransistor 34 transmits the pulses coming from the microprocessor 12 on the data lines 18 to the next station 40. The data pulses on lines 38 are identical to the data pulses on lines 14, coming from the microprocessor 12, and they short-circuit the passive element, namely a light-dependent resistor or a phototransistor 43 of the optical coupler 42 , so that a current flows from the direct current source, through the active elements, namely the light-emitting diodes 45 and 47 of the optical couplers 44 and 46. The output signal of the optical coupler 44 provides the data station 40 with the pulses of data from the interface circuit 21 and the output signal from the optical coupler 46 provides pulsed data information to the next station (data station 3) as shown in FIG. 1. It thus appears that the circuits d he data interface according to the invention can be used in cascade to transmit and retransmit data pulses to any number of stations, practically without limit. It should be noted that the data pulses coming from the microprocessor 12 appear on the data lines 38 even if the station 22 is not in operation, for example when it is stopped for its maintenance.

For the purpose of transmitting data, a station such as the first data station 22 applies pulses to the light-emitting diode 20 of the optical coupler 16. This reduces the impedance of the element 18 which acts on the optical couplers 24 and 30 in series in the same way as the data pulses received on the lines 14 coming from the microprocessor 12. The light produced by the light-emitting diode 20 lowers the resistance of the phototransistor 18 so that a current flows there and turns on the light-emitting diodes 26 and 32. The light pulses from the diode 32 are received by the phototransistor 34 which reproduces these pulses at its output connected to the data lines 38. Thus, the data pulses are transmitted on the data lines 38 to the circuit d interface 41 of the second data station 40. In addition, the data pulses are available at the output of the phototransistor 28 of the optical coupler 24 and can be read by the station he data 22 in the form of an immediate control of the data which he transmits. It thus appears that, as shown in FIG. 1, any data station can transmit to any other downstream station and that any extension can receive data from all other upstream extensions.

 Numerical data can be addressed to any one of a particular group of data stations using address prefixes added to the data. Each station is then programmed or connected so as to react to a particular digital address. In addition, in an assembly according to the invention, since data is transmitted by passing by an unaddressed station rather than by crossing it, by incorporating a dead band delay in the data stations, an unaddressed station can be produced in such a way as to neglect a program which is not intended for it.

This essentially requires a circuit or programming which interrupts the operation of the data entry section of a station when an address prefix of a different station has been detected on the data lines. The station continues to monitor the data lines during the idle time.

After a dead time interval (for example 7 milliseconds), the unaddressed data station switches back on its data input section and checks the data lines awaiting a transmission addressed to it.

FIG. 2 represents a set of data interfaces according to the invention, in the closed loop configuration. The assembly includes a central station 50 in which an interface circuit 51 is connected to a microprocessor or other device 52 for inputting and transmitting data, in the same manner as that described above. A pair of data lines 53 transfers pulses of digital data in series to a first data terminal 54. The first terminal 54 also includes the interface circuit 55 connected to a data station 56. The output signals from the first terminal 54 are transmitted on a pair of lines 57 to a second terminal (not shown), and so on, up to an nth terminal 58. The nth terminal 58 likewise comprises an interface circuit 59 and a data 60. The output of the nth terminal 58 is brought back on a pair of data lines 61 to the central station 50 to be connected via an interface 51 to a signal input of the processor 52. The transmission assembly of serial digital data shown in Figure 2 is a closed loop system which not only allows immediate control by the processor 52 of the data it transmits, but which also allows any data station in the set to transmit d data to any other station, either upstream or downstream, since the data signal travels over the entire closed loop to return to the station which transmits.

Thanks to the use of an addressing system and a dead band control, any station can address any other connected in the closed loop. The two stations can then communicate in one direction and in the other insofar as the circuit must not remain inactive during the predetermined duration of the dead band. When the communication is finished and the circuit is at rest for the predetermined period, all the stations are put back into service and any of them can address and communicate with any other.

The interface circuit shown in FIG. 1 does not work satisfactorily in a closed loop assembly such as that shown in FIG. 2. This is due to the fact that when one of the stations applies a data pulse to the loop, this whole loop goes to logic level "1". This logic level "1" then continues indefinitely even after the pulse has been interrupted by the transmitting station.

 FIG. 3 therefore represents a modified interface circuit 70, connected to a data station 71 which is arbitrarily designated as station nO i. The station 71 can be any of the stations comprising the microprocessor 52, the station 56 or the other stations of the closed loop of FIG. 1. The interface circuit 70 comprises a pair of data input lines 73 which are connected to the output of the interface circuit of the previous station in the closed loop and a pair of data output lines 74 which are connected to the input of the interface circuit of the next station in the loop. The interface circuit 70 also comprises a pair of data input lines 75 coming from the station 71 and a pair of data output lines 76 connected to the station 71. The interface circuit 70 generally comprises four optical couplers 77 to 80. A low voltage power source, for example a current source of direct current at 5 volts, is connected by a terminal 81 to a circuit comprising a resistor 82 for limiting the current, a light-emitting diode 83 in the coupler 78, a light-emitting diode 84 in the coupler 77 and the data input lines 73 to ground 85. When a data pulse is received on lines 73, coming from the previous station, the circuit is closed and energized light-emitting diodes 83 and 84.

The diode 84 is optically coupled with a phototransistor 85 connected to the output lines 74 so as to apply the pulse to the next station in the closed loop. In a similar manner, the light-emitting diode 83 of the optical coupler 78 is optically coupled with a phototransistor 86 which applies the data pulse received on the input lines 76 to the station 71. The optical couplers 79 and 80 operate when data is sent by the set 71. Generally, the optical coupler 79 applies the output data from the set 71 to the output lines 78 and the optical coupler 80 inhibits any transmission from the input lines 73 to the output lines 74. The optical coupler 79 comprises a light-emitting diode 87 and the optical coupler 80 comprises a light-emitting diode 88 these diodes being connected in series across the terminals of the output lines 75 coming from the station 71. When the station 71 applies an output pulse to the line 75, the two light-emitting diodes 87 and 88 are excited. The diode 87 energized in the optical coupler 79 excites the phototransistor 89 connected between the output lines 74, in parallel with the phototransistor 85. Thus, the output data from station 71 are applied on line 74 to the next data station in the closed loop. The lit diode 88 excites a phototransistor 90 in the optical coupler 80. The phototransistor 90 is connected so as to short-circuit the diode 84 of the optical coupler 77. Consequently, a data pulse received on the input lines 73 coming from the previous station in the closed loop is derived from the optical coupler 77 while the station 71 transmits data.

But the input pulse received on the lines 73 still turns on the light-emitting diode 83 of the optical coupler 78. This allows the data transmitted by the station 71 to traverse the entire loop up to the optical coupler 78 and therefore up to the lines entrance 76 of post 71, for verification. Since the data which traverses the entire closed loop does not cross the optical coupler 77, this loop normally returns to the low level or "0" when an output pulse from the station 71 stops on the line 75.

Optionally, a relay can be connected between the input and output lines in each of the interface circuits of Figures 1 and 3. The relay of each interface circuit is normally kept open by the low voltage power source which powers the interface circuit.

In the event that the power source fails or when a station is put out of service, the relay closes its contact to connect the input lines of this station with the output lines so as to maintain the continuity of the together.

 It is obvious that many modifications can be made to the embodiments described and illustrated by way of examples without departing from the scope of the invention. In the above description, the term "optical coupler" designates any type of radiating energy coupling device whose response time is short enough to handle the data transmitted in the system incorporating the interface circuit.

Claims (8)

 1 - Serial digital data interface circuit intended to connect a data transmission and reception station comprising an input and an output to the output of a previous station and to the input of a next station, circuit interface characterized in that it comprises first, second and third optical couplers each comprising a driving element optically coupled with a controlled element, a voltage source, a device for connecting the driving elements of the first and second optical couplers and of the controlled element of the third optical coupler in series with said voltage source, a device for connecting the output of the previous station in parallel with said controlled element of said third optical coupler, a device for connecting said element attack of said third optical coupler at the output of said data transmission and reception station, a device for connecting said controlled element of said second optical coupler to the gut of said data transmission and reception station and a device for connecting said controlled element of said first optical coupler to the input of said next station. 2 - Interface circuit according to claim 1, charac terized in that said driving elements consist of light emitting diodes. 3 - Interface circuit according to claim 1, characterized in that said controlled elements consist of phototransistors.  4 - Interface circuit according to claim 1, characterized in that said controlled elements consist of resistors dependent on light. 5 - Device for transferring data pulses in series between several data stations arranged in a sequence, each data station comprising an input and an output, device characterized in that it comprises a separate pair of conductors between two neighboring stations in the sequence, a separate interface circuit associated with each station, each interface circuit comprising a first optical coupler with a driving element connected to a first input and optically coupled with a controlled element connected to a first output, a second optical coupler with a driving element connected to a second input and optically coupled with a controlled element connected to a second output, a third optical coupler with a driving element connected to a third input and optically coupled with a controlled element connected at a third output, a voltage source, a device for connecting in series said voltage source, said first e input, said second input and said third output, a device for connecting said first output to the conductors leading to the next station in the sequence, a device for connecting said second outlet to the input of the station associated with this circuit interface, a device for connecting said third input to the output of the associated station and a device for connecting said third output to the conductors coming from the previous station in the sequence.  6 - Serial digital data interface circuit intended to connect a data transmitting and receiving station comprising an input and an output to a data input line coming from a previous data station and to a line output circuit leading to a next data station, interface circuit characterized in that it comprises a first optical coupler which connects said data input line to said data output line, a second optical coupler which connects said data input line to said input of said data reception and transmission station and a third shot their optics which connects said output of said reception and data transmission station to said data output line.  7 - Interface circuit according to claim 6, charac terized in that it further comprises a fourth optical coupler controlled by said output from said data reception and transmission station so as to block the passage of data from said data input line to said data output line. 8 - Interface circuit according to claim 7, characterized in that each of said optical couplers comprises an input optically coupled with an output, said interface circuit further comprising a device for connecting the inputs of said first and second optical couplers to said data input line, a device for connecting the outputs of said first and third optical couplers to said data output line, a device for connecting the inputs of said third and fourth optical couplers to said output of the receiving station and data transmission, a device for connecting the output of said second optical coupler to said input of said reception and data transmission station and a device for connecting the output of said fourth optical coupler to the input of said first optical coupler .