FR2546012A1 - Method of two-way transmission of data by optical fibre over a serial bus and terminal device connected to this bus in order to implement this method - Google Patents

Abstract

The method according to the invention comprises the steps of transmitting a first particular binary word via a transmitter terminal Tn, the other terminals Tn-2, Tn-1, Tn+1 being in a "standby" state, the recognising of this word by the upstream and downstream terminals, the setting of these terminals Tn-2, Tn-1, Tn+1 into a detection/-regeneration state, the repeating of these steps until the word is received by the terminals at the ends of the bus, the transmitting of the useful information and the transmitting of a second particular binary word repositioning the terminals in the "standby" state. The method allows two-way transmission of data via a single optical fibre open-loop serial bus Fn-2,n-1 to Fn+1,n+2.

Description

METHOD FOR BIDIRECTIONAL DATA TRANSMISSION
OPTICAL FIBER OVER SERIAL BUS AND TERMINAL DEVICE
CONNECTED TO THIS BUS FOR THE IMPLEMENTATION OF THIS METHOD.

 The present invention relates to a bidirectional transmission method on a serial fiber optic bus. It also relates to a terminal device connected to this bus implementing the method.

 The well-known advantages of optical fibers make them attractive as transmission means in the conversational links replacing electric bus lines. In addition to a higher information rate and a total immunity to electromagnetic interference, optical fibers indeed have the interest of eliminating the impedance matching and ground loop problems usually encountered in electrical transmissions.

 As with electrical guide links, two main configurations of data distribution systems are found: the series distribution and the star distribution. The present invention is concerned with the series type connection.

The architecture of the serial link systems can also take two main forms: the open loop or the closed loop to which are connected a predetermined number of terminals. These terminals comprise input members and output members for receiving and transmitting electrical signals. These terminals are further connected to the optical fiber serial bus by means of coupling members. These coupling members were generally in the oldest systems constituted by passive type couplers. Such couplers are described by way of example among others in the article published in the technical journal
THOMSON-CSF Vol. 13, No. 4, December 1981, pages 1059-1083.

 In more recent systems, it is generally preferred active couplers composed of optoelectronic organs converting light signals into electrical signals, on the one hand, and electrical signals into signals guided by the optical fiber constituting the channel on the other hand. link.

 Where permitting, i.e. essentially when the transmission distances are not too great, the bus can be operated in a closed loop so as to reach any of the terminals, operating as a receiver terminal, from a transmitter terminal. However, this requires a specific protocol in order to locate the last terminal reached and to stop the transmission of information at this point.

 In the case of terminals arranged in an open-loop configuration, ie generally separated by a long length of optical fiber, it is preferred to double the equipment in order to ensure the bidirectional propagation of information from any of the transmitting terminals. The link channel then comprises a first unidirectional channel transmitting the information in a first direction and a second unidirectional channel transmitting the information in the opposite direction.

 This architecture therefore requires the use of two optical fibers for a link path and a doubled number of expensive devices such as connectors.

 The invention is placed in the context of an open loop serial link and aims to overcome the disadvantages of the known art. It proposes a method of bidirectional transmission of data requiring only a single optical fiber as a connection channel between the terminals and allowing the propagation of information from a transmitting terminal without risk of faulty operation, ie in positioning the other terminals, upstream and downstream, in states suitable for this propagation.

The subject of the invention is therefore a method for bidirectional transmission of data by optical fiber in a system comprising an open-loop serial bus and terminals distributed in cascade on this bus, each terminal being connected to a downstream terminal and to an upstream terminal. by said bus and can, in turn, be in transmitter mode or in receiver mode of a light wave guided by said optical fiber constituting the serial bus and carrying the information to be transmitted; characterized in that it comprises:
an initial step of setting the receiver mode terminals to a first standby state for which these terminals scan the state of the downstream and upstream terminals of the serial bus to which it is connected;
a transmitting step by a terminal used in transmitter mode, for a given time, of a first specific binary word downstream and upstream, via a section of single optical fibers arranged between the terminals; and constituting said serial bus;
a step of detecting and recognizing this first specific bit word by the downstream and upstream terminals of the transmitting terminal;
a step of regeneration and re-transmission of this first recognized specific binary word, respectively downstream for the downstream terminal and upstream for the upstream terminal;
a step of repetition of these two steps so as to ensure, step by step, the propagation downstream and upstream of said first specific bit word to the terminals arranged at the ends of the serial bus;
a step of sending a message of information by the transmitting terminal;
a transmission step at the end of this message by the sending terminal of the second specific bit word downstream and upstream of the serial bus to which it is connected;
a step of detecting and recognizing this second specific bit word by the downstream and upstream terminals;
a step of regeneration and re-transmission of this second specific bit word by these terminals and the return to the standby state of the downstream and upstream terminals after this retransmission;
and a step of repetition, step by step, of these two steps to the terminals arranged at both ends of the serial bus.

 The invention also relates to a terminal device for implementing the method.

The invention will be better understood and other advantages will appear with the aid of the description which follows, with reference to the appended figures and among which:
- Figures 1 and 2 show in fiber optic serial bus link systems according to two configurations of the prior art;
FIG. 3 represents an optical fiber serial bus link system according to the invention;
FIG. 4 represents an example of a concrete embodiment of the terminal device according to the invention;
FIG. 5 diagrammatically represents the time configuration of the data exchange according to the method of the invention;
FIG. 1 schematically represents the architecture duras a closed-loop connection system whose serial bus consists of a single optical fiber F '. In this organization, the terminals represented in the number of n are inserted in series with single optical fiber IFO Each terminal, TI to
T'n comprises two modules, all identical, a transmitter module injecting into the optical fiber iE 'a wave conveying the information to be transmitted and a receiving module receiving the guided wave and converting it into electrical signals.

 The information can be incorporated into the light wave by a known method: amplitude modulation, frequency modulation, or pulse modulation.

Each terminal also includes an entry E'1 to In receiving the
n electrical signals representing the information to be transmitted and a sound output, transmitting the electrical signals representing the detected information to user organs not shown in the figure. As has been recalled, this configuration can only be used if a protocol is used to identify the last terminal reached and stop the flow of information, and secondly, when the distance between terminals is not too important. Also for long distance transmissions, open loop systems are preferred. It is then necessary, for bi-directional transmissions of information to split the link channels. Figure 2 illustrates such a configuration.

In FIG. 2, four terminals T 'to Tn have been represented. Each terminal is then composed of two modules, transceiver, all identical, m "i and iT '.The first modules, ml', are connected to a first optical fiber flassurent undirectional links in a first direction and the second modules, rrM 'are connected to a second optical fiber f2 providing unidirectional connections in opposite directions, each terminal also comprises, as before, an input of electrical signals, En 3 to En to which the inputs of the two modules m1 and In fact, in the configuration illustrated in Figure 2, each module, m1 'and mM', plays a similar role to the terminals 1;
Figure 1. Also each module, ml and m2, is provided with a signal output
respectively, Si ', n-3 to S "and S2, n-3 t to
I, n 5211, n-3 so
This configuration therefore requires the use of two optical fibers
fl and f2 for each linkage and the use of associated organs
such as optical connectors. Indeed, when the distances separating two
successive terminals are important, it is not generally possible
to obtain optical fibers made in one piece.It is then necessary
to make optical connections, either fixed or removable.

The aim of the invention is to limit these disadvantages and proposes a process which,
while allowing for two-way data transmission,
requires that the use of a single optical fiber.

We first described an example of a terminal device implementing
the process of the invention. This process will be explained from the
description of this device;
Figure 3 schematically illustrates a bidirec link system
on an open loop serial bus using only one fiber. Sure
this figure, it has been shown four terminals according to the invention
Ton 2 to Tn + ig these indices being chosen by pure convention and the total number
terminals can be any. Each terminal can be either
transmitter or receiver in turn. It will be supposed to fix the ideas in the following that the terminal T n is transmitter. Each terminal is connected to
two terminals, one upstream and the other downstream, using an optical fiber
single f. As before, the terminals are equipped with the entrance of
electrical signals, En2 to En + l, and electrical signal outputs, Sound 2 to 5n + I
By taking the convention that has just been admitted, the terminal T n is
transmit the same signal in the form of a guided light wave downstream,
that is to say the terminal Tn + 1, upstream, ie the terminal Tn 1 These
terminals will re-transmit these signals, one, Tn + 1, downstream, and the other, T
not-
upstream, ie towards the terminal Tn2 in FIG. 3.

FIG. 4 illustrates a practical embodiment of a terminal
according to the invention. Although all terminals are preferably identi
In the following, it will be assumed that the terminal illustrated in FIG. 4 is the terminal T of FIG. 3. This terminal is optically coupled to one end.
not
to the terminal Tnfl by a single optical fiber section fn + b and, on the other hand,
on the other hand, at the terminal Tnî by a single section of optical fiber fn
Each terminal actually comprises two transmitter-receiver circuits
electrical signals, I and II. For convenience, circuit I will be called
in what follows "upstream circuit" because it is optically coupled to the end
of the optical fiber Fn 1 n connecting the terminal T n to the terminal T ni 'and the
circuit n will be called "downstream circuit" because it is coupled to the end of the fiber
Optical zero fun connecting the terminal T Tnsl terminal.

not
Preferably, the conversions of the light signals into
electrical signals and conversely electrical signals into signals
are made by a single optoelectronic device consisting of a diode capable of operating alternately as a transmitter and
light energy detector of the same length. This component is
described in patent FR-B-2 396 419, patent relating to a semi diode
conductor that polarizes in the forward direction, emits light and
polarized in the opposite direction, is able to detect light of the same wavelength.

The transmission-reception circuit I thus comprises such a diode D1
coupled to another unit by the optical fiber Fn, n + 1 The anode of this diode
is connected to a potential that is supposed to be the potential of the earth. The
cathode of the same diode D1 is connected to a two-way switch K1 K11 and K12 respectively. At the idle state, the channel K11 is passing.
and connected to the input of the amplifier 31 for amplifying the current
provided by the diode when it captures transmitted light energy guided by
the fiber fn, the output of this amplifier 31 is transmitted to the input
of an electronic shaping element 41, for example triggering
Schmitt type for outputting a binary signal at a first state, for example logic state "1" when the signal converted by diode D1
exceeds a predetermined threshold and a signal to the other logic state "0" when
the amplified signal is below this threshold.
to get rid of parasitic signals carried by optical fibers. The exit
of the shaping circuit 41 is connected to the input of logic circuits of
comparison 1. These comparison logic circuits 1 comprise a
serial input shift register receiving the signals transmitted to the input
ER1 and SS1 serial output. The shift register 10 also has parallel outputs Spl. As is known, this type of register generally consists of a series of bistable organs arranged in cascade.

The parallel outputs are then the outputs of each of these bistable organs, for example flip-flops. The parallel outputs Spl are transmitted to the inputs of two binary decoders, respectively 11 and 12. As will be described later, these two decoders 11 and 12 are responsible for recognizing two distinct logical configurations and, on the recognition of these logical configurations, generate a binary signal, respectively SDll and 5D12 transmitted to a bistable member 13.This bistable member which can be constituted for example by RS type flip-flop is set to a specific logic state, for example the logic state "1", when the signal SDll is active and in the "O" inverse logic state, when the signal SD12 is active in turn.

 The transmitting-receiving circuits II comprise elements identical to those which have just been described, namely an emitter-receiving diode Ex2, a two-way switch K K21 and K22, the channel K21 being connected to the input ER2 of comparison logic circuits 2 via an amplifier 32 and a shaping member 42, these logic circuits also comprising a shift register 20 with parallel inputs and serial output SS2 and parallel outputs Sp2, two decoders 21 and 22 and a bistable element 23 .

 The bistable elements 13 and 23 control the change of state of the switches K1 and K2; respectively the switch K1, by the output signals S23 of the bistable 232 and the switch K2, by the output signals S13 of the bistable 13.

 The channels K22 and K12 of the switches K2 and K1 are connected, on the one hand to the cathodes of the diodes D1 and D2, and on the other hand, by a common connection to the output of an amplifier 6 receiving on an input In signals intended to be transmitted over a serial bus link.

 The transmission of these data is authorized by an output signal of an "OR" logic gate whose two inputs are respectively connected to the outputs of the shaping elements 41 and 42. The output of the "OR" gate 5 is connected to a second input of the amplifier 6.

 The operation of such a terminal will now be described in more detail. When the terminal is transmitter, the channels K11 and K21 are open as shown in FIG. 4, and the channels K12 K2 and K22 are closed so as to establish a continuous electrical connection between the output of the amplifier 6, on the one hand , the cathode of the diode D1 and the cathode of the diode D2, on the other hand. It should be understood that, although represented in the form of electromechanical elements, the switches K 1 and K; can take all forms approlpriées and in particular be electronic type of horns controlled by output signals flip-flops 13 and 23. It is also assumed that the light waves emitted by the diodes D1 and D2 are impulse type waves, c that is, the information to be transmitted is directly in binary form; the binary logic states being represented by the presence or absence of guided light. This form of modulation is not limited to rinsing. By adapting the amplification circuits 6, the information can be transmitted in another form: amplitude modulation, frequency modulation, etc. This aspect is outside the scope of the invention and is well known in the art. job.

 The diodes D1 and D2 will therefore transmit simultaneously, downstream and upstream, the same information in the form of light pulses. It is assumed that the electrical signals delivered by the amplification circuits 6 are of polarity and amplitude suitable for obtaining, the operation of the diodes D1 and D2 light emitter according to information of the aforementioned French patent.

 When the terminal is used as a data transmitter, the channels K and K21, as shown in FIG. B, are open, that is to say that the links between the cathode of the diodes D1, on the one hand, and D2> d on the other hand, and the inputs of the associated amplifiers 31 and 32 are interrupted.

The output of the logic gate "OR" 5 is at a determined logic state allowing the amplification of the data present on input E, for example in the "O" logic state.

When the terminal is used as a receiver, two states are possible: the standby state and the detector-regenerator state. As will be described in the following, at the end of each message from a transmitting terminal, for example the terminal Tn in Figure 3, all other terminals are put in standby state. In this state, the diodes D1 and
D2 are made detectors, K11 and K21 channels are made and channels K12 and K22 are open. The terminal can then simultaneously detect the signals transmitted upstream, that is to say those carried by the optical fiber Fn-1 ns, and those emitted downstream, ie the signals conveyed by the optical fiber fn rH-1 In the state of detector-regenerator, one of the
n, n + l transceiver circuits, I or 11, is transmitter while the other is receiver. It is assumed here that the circuit I is receiver while the circuit H is transmitter. For this purpose, the diode D1 is detector, the channel K11 closed and the channel K12 open, while the diode D2 is used as a light emitter, the channel K21 being open and the channel E <22 closed. The output signal of the The formator circuit 41 is transmitted via the logic gate "OR" 5 to the input of the amplifier 6, the output of which modulates the signal emitted by the diode D2, which signal is therefore retransmitted by the optical fiber fn 1 n towards the terminal terminal Tn The signal received from a downstream terminal T n is therefore retransmitted to the upstream terminal Tn 1, ie regenerated. Furthermore this signal is available on the serial output SS1 of the shift circuit 10. The outputs SS1 tet S52 can also be made to a common organ and retransmitted as a unique connection Sn, Sn4 to 2
n + I (Figure 3).

 The use of such a terminal requiring the transition from the standby state to the detector-regenerator state in the correct direction relative to the location of the transmitting terminal.

 According to the method of the invention, this passage is carried out by means of a specific transmitted binary word having any message by the transmitting terminal. This word M1 is detected by the two nearest terminals, upstream and downstream, of the transmitting terminal and is compared in the comparison circuits of these terminals, respectively I and 11. This task is performed more specifically by decoders 11 or 21. On recognition of the code word M1, the decoder generates a signal, SD11 or SD22 'for activating the bistable members 13 or 23. These act on the switches K2 or K1 as previously described and cause the termianl to change. from the standby state to the detector-regenerator state in the correct direction.

Repetition by the sending terminal of the specific word is required
to provoke, step by step, the passage of all the others
terminals from the standby state to the detector-regenerator state. For some
reasons of simplicity, the transmission time of the specific word M1 can be
set "worse case" ie the transmission time corresponding to a
transmitter terminal placed at one of the ends of k bus line.

At the end of this time, the transmitting terminal can then transmit the
message corresponding to the information. As it is known, this message
may include in the header address words indicating one or more
particular terminals among the connected terminals, to which the informa
is intended. These points are beyond the scope of the invention and are common
to the known art.

According to a second aspect of the method of the invention, at the end of this
information message, a second specific binary word M2 is issued by
the transmitting terminal. This specific word is detected and re-emitted by
terminals in the detector-regenerative state and causes the passage of all
these terminals from the detector-regenerator state to the standby state. This
task is performed more specifically by the decoder, respectively 12 and
22, included in the comparison circuits 1 and 2. When recognizing
the decoders, these generate on their outputs a; 1; 5gnal, respectively SD12 and SD22 of deactivation of the bistable organs.
13 and 23 which in turn act on the switches K1 and K2 of the
way that was previously described The actual passage of the state
detector-regenerator in the waking state does not take place on each terminal
only after retransmission of the specific word M2.

Figure 5 illustrates the time configuration of a complete program
comprising a header consisting of specific M1 binary words transmitted
during the maximum time t ill followed by an informational message, and
terminated by the binary specific word M2. The particular configuration of the
The message may also be governed by specific protocols to
system, messages of fixed lengths or variable lengths for example.

 This aspect also falls outside the scope of the invention.

In addition to the diodes D1 and D2 which are of the type described in the application of
French patent mentioned above, and known under the trade name diode ERGS, the other components can be selected from those available in the catalogs of manufacturers of integrated circuits. Their choice also depends on the precise technology adopted and is within the reach of the skilled person.

 Referring back to FIG. 3, the number of memory positions of the shift registers 10 and 20 is at least equal to the number of bits or bits of the specific bit words M1 and M2. It can be naturally larger, for example to record several words of the information message.

The steps of the method according to the invention can therefore be summarized as follows:
an initial step during which all the terminals are put in the standby state;
a step during which the terminal, used in transmitter mode, transmits for a given time a first specific bit word M1, downstream and upstream;
a step of detecting this word M1 and its recognition by the downstream and upstream terminals;
on this recognition, a step of setting to the detection state regeneration of these terminals, state for which the word M1 is regenerated and re-transmitted, respectively downstream for the downstream terminal and upstream for the upstream terminal;
repetition steps of these two steps so as to ensure, step by step, the propagation downstream and upstream of the transmitting terminal of this specific bit word M1 until two terminals arranged at the two ends of lines;
a step of resending an information message intended for at least one of the terminals
a step of transmission by the transmitting terminal of a second specific word M2 downstream and upstream
a step of detecting and recognizing this second specific word M2 by the two downstream and upstream terminals;
a step of regeneration and retransmission of this word, respectively downstream for the downstream terminal and upstream for the upstream terminal, and of putting in standby state of these terminals after the retransmission; ;
and steps of repetition step by step of these steps to the terminals arranged at the ends of the line.

Claims (3)

 A method of bidirectional transmission of data by optical fiber in a system comprising an open loop serial bus and terminals (Tn-2 to Tn + 1) cascaded on this bus, each terminal being connected to a downstream terminal and to an upstream terminal by said bus and can, in turn, be in transmitting mode or in receiver mode of a light wave guided by said optical fiber constituting the serial bus and conveying the information to be transmitted 5 characterized in that it comprises ::  an initial step of setting the terminals (tn-2 to Tn + 1) in receiver mode to a first so-called standby state for which these terminals scan the state of the downstream and upstream terminals of the serial bus to which it is connected;  a transmitting step by a terminal (Tn) used in transmitter mode, during a determined time (tmaxX of a first specific binary word (M1) downstream and upstream, via a section of single optical fiber (Fn-2, n-1 to Tn + 1, n + 2) disposed between the terminals and constituting said serial bus;  a step of detecting and recognizing this first specific bit word (M1) by the downstream (Tn + 1) and upstream (Tn 1) terminals of the transmitting terminal (Tn);  a step of regeneration and retransmission of this first recognized specific bit word (M1), respectively downstream for the downstream terminal (Tn, l) and upstream for the upstream terminal (Tn 1);  a repetition step of these two steps so as to ensure, step by step, the propagation downstream and upstream of said first specific bit word (M1) to the terminals arranged at the ends of the serial bus,  a step of sending an information message by the transmitting terminal (T i  - A transmission step at the end of this message by the transmitting terminal (Tn) of a second specific bit word (M2) downstream and upstream of the serial bus to which it is connected; the two-way switch (K1, K23 included in the other module (11, I).  6. Device according to claim 5, characterized in that the memory circuit (10,20) is a serial input shift register (ru1, ER2) and comprising parallel outputs (Spl, Sp2) in number at least equal to the number bits of the first and second specific binary words.  7. Device according to claim 5, characterized in that the bistable member (13,23j is a flip-flop type "RS".  8. Device according to any one of claims 3 or 4, characterized in that the means (5) for combining the received electrical signals comprises a logic gate 'oun receiving on two inputs the outputs of the receiving means (41, e2) electrical signals and whose signals present on the output are transmitted to the common means (6) for transmitting electrical signals.

 9. Device according to any one of claims 3 or 4, characterized in that the means for receiving the electrical signals comprise an amplifier (31,32) in cascade with a shaping threshold circuit (41,42). amplified signals to generate steep-edge pulse type output signals transmitted to the comparison logic means (10,20) and the combination means (5).

<Tb> <tb> <SEP> mcx <tb> o- <SEP> t <tb> o <SEP> - <tb> <SEP> v <tb> <SEP> M1 <SEP> MESSAGE <tb> <SEP> flG.5 <tb> <SEP> FlG.5  and a repetition step, step by step, of these two steps up to two terminals arranged at both ends of the serial bus.  a step of detecting and recognizing this second specific bit word (M2) by these terminals and returning the downstream (Tnsl) and upstream (T) terminals to the standby state after this retransmission;  2. Method according to claim 1, characterized in that the determined time is the maximum time (t) necessary to ensure the propagation of the first binary specific word (M1) of a transmitter mode terminal located at one end of the serial bus to a receiver mode terminal at the other end of the serial bus.  3. Terminal device (Tn) for implementing the transmission method according to any one of claims 1 or 2 connected to a covered loop optical fiber serial bus; characterized in that it comprises two modules (t, II) transceiver of light radiation carrying information to be transmitted; the first module (1) being coupled by said serial bus to an upstream terminal (TnI) and the second (I1) to a downstream terminal (ton + 1); the serial bus comprising sections (Fn 1 ns Fgn + 1) of single optical fiber arranged between the terminals; and in that each module (I, 11) comprises optoelectronic means (D1, D2) for transmitting light radiation coupled optically to the serial bus, con> ering light radiation to electrical signals and electrical signals representing radiation information. luminous, receiving means (31-41;; 32-42) ampflfiant and shaping the electrical signals from the conversion, means (6) for emitting electrical signals common to both modules, a switch (K1, K2), (K11-K12, K21-K22) establishing selective connections, exclusive of each other, between, on the one hand, the optoelectronic means (D1, D2) of the emission-reception of light radiation and, on the other hand, the reception means (31-41, 32-42) or the means (6) for transmitting electrical signals, logic means (1,2) for comparing binary words received by the means comparison (1 or 2) of a (I or 11) ge modules denoting a control signal (S13 or S14) of the switch (K2 or K1) of the other (11 or I) modulates a connection between the optoelectronic means (D1 or D2) of emission-reception of light radiation and the