FR2535133A1 - Facility for digital transmission, by bifilar line, of information supplied by sensors and of orders intended for actuators. - Google Patents

Abstract

This facility comprises a bifilar line L1 L2 and transmitter-receiver stations NA0, NA5 connected to this line and each provided with card digital NC-EN and/or card analog NC-EA parallel input paths and with card digital NC-SN and/or card analog NC-SA outputs and with means UART of serialising the corresponding information. The cards NC1, NC2 and the stations NA-0, NA-1 are each identified, by the central processing unit UC of each station, by means of a binary number. The central processing unit continually receives messages, of predetermined duration, originating from all the other stations in service, but exploits only the information originating from those of the input cards which have the same identification numerals as its own output cards.

Description

DIGITAL TRANSMISSION INSTALLATION, BY BIFI LINE
LAIRE, INFORMATION PROVIDED BY SENSORS AND ORDERS
FOR ACTUATORS.

The subject of the invention is an installation for the digital transmission, by two-wire line, of information supplied by sensors and of orders intended for actuators.

In the monitoring and control of manufacturing processes or machine states, the continuous increase in the number of information to be transmitted from sensors and orders to be executed by actuators leads to increasing complexity of installations and to congestion. exceesif das control rooms in wire conveying information. n indeed, the various analog or digital quantities to be transmitted are generally by means of separate pairs of them and it is necessary to multiply the multi-wire cable trays and the connection terminals, which results in a very significant cost in material and installation.

It has already been proposed (Article by M. Sulpice, G. Chevalier in the review Automatisme, No 1-2 1976, pages 32-58) to use a two-wire transmission line providing the link between an acquisition and control unit coupled to a computer and stations distributed throughout the installation.

Data and orders are routed to, or from, the various stations using two-way serial transmission along the line. This device is however relatively complex, because all the information exchanges are managed by the acquisition unit and it is the latter which is responsible for ensuring synchronism.

The invention aims to achieve a very simple device, intended to ensure the permanent transmission of information and orders, therefore of equivalent function to that of a simple cable tray and in which a dialogue procedure, incorporated in the stations themselves. -memes, ensures all exchanges without the need to have recourse to a central computer.

The invention also aims to produce an installation of the aforementioned type, in which stations can be switched on / off at will, without disturbing the exchanges between the other stations.

The installation according to the invention comprises a two-wire transmission line and a plurality of transmitter-receiver stations connected to this line and each provided with one or more parallel channels of digital and / or analog inputs and digital outputs and / or analog and serialization means of information corresponding to these channels, characterized, in combination a) by the application, to the two-wire line, of a voltage
feed that the information items "all or
nothing "provided by the stations have the effect of putting
short-circuited to define one of the two levels
corresponding logic b) by materializing the channels in the form of a
plurality of cards each identified by a number
binary and connectable at will to each station and
by an arrangement of the installation to allow the
commissioning at will, of a variable number of sta
each identified by a binary number c) by the fact that each station comprises a unit cen
trale arranged to identify the identifi
cation of stations and maps d) by establishing a desired configuration which
conch connections by arranging the central unit of
each station so that it constantly receives
messages, of predetermined duration, originating from the
appears to be other stations in service, but does not operate
that the information coming from that of the cards
entries that have the same identification numbers as
own exit cards; and e) by an arrangement of the central units of the stations such
that the transmission of messages by stations in service
intervenes cyclically, in the order of their
increasing identification numbers, during inter
successive time intervals of each reserved cycle
each to the emission of a message by a station well
determined whether it is in service or not and in
number equal to the maximum number of stations provided for
the installation.

According to a preferred embodiment of the invention, the central unit of each station is arranged: a) to generate, from the power up of
said station, a time delay equal to
product of said maximum number of stations by a delay
unitary at least equal to said duration of a message b) to generate, upon receipt of information
start of messages a new unit tempo delay
rization; c) to recognize the end of a received message and identify
11 device that issued it; d) to send a message itself at the end of the message
previous when it has been correctly received and
identified as coming from the previous number station
dent te) otherwise, to generate, at the end of the period
referred to in (b), as many additional unit delays
that there are intermediate stations whose message has
not been properly received and to issue itself a
message at the end of these additional periods.

Other features, as well as the advantages of the invention, will become apparent in the light of the description below.

In the attached drawing
Figure 1 is a general block diagram of a
installation according to the invention; whose
Figure 2 shows a transmitting station
receiving
Figure 3 shows a digital input card
ques;
Figure 4 shows a digital output card
what t and
Figures 5 to 9 illustrate the operation of
the installation, showing the timing distribution
time delay messages and signals.

In Figure 1, there is shown a two-wire transmission line L1L2 supplied, by a block AL, by a regulated direct voltage of 12 v for example, obtained from the AC network in a manner known per se and delivered under a well-determined impedance .

A number of NA-O ... NA-5 data transceivers (16 for example) are connected to this line, each of which is associated with several input-output cards NC-1 EN, NC-2 SN .... each assigned an identification number (ranging from 1 to 8 for example).

The cards marked EN are digital input cards, EA cards, analog input cards, SN cards are digital output cards and and SA cards are analog output cards.

 @a figure 2 shows one of the transceiver devices. It is composed of a set UC comprising a central unit, with random access memory and read only memory, of an ES device which performs, in addition to the management of the inputs / scrties of the central unit, the decoding of the addresses R d ' an asynchronous "UART" serial transmission device connected to line L1L2 via a PCE transmission photo-coupler, a PC reception photo-coupler, a T transistor and a diodes R.

 @ the emission, the transistor or is passing for one of the two logic @ @ digital signals transmitted, blocked for the other. When the transistor is blocked, the voltage of 12 volts is applied to the line. When it is on, the line is short-circuited.

@ reception, the rectangular signals transmitted on the
@@@ e are sent directly to PCR.

@@@ input-output ports are connected to the device by means of connectors, not shown (8 in number in
@ 'example considered).

To the device ES are connected a switch RA for manual coding of the number of the transceiver device (comprised between 0 and 5 in the example considered), a device AD for displaying faults which, at the time of power up, signals to the operator the existence of a fault detected by a test triggered by the central unit, and an isolation circuit A @ of amplification, whose output S commands for example an indicator light to the operator that the device is in normal sex.

Figure 3 shows a digital input card. The information from sensors is applied to the inputs EN1 ... EN8 and transmitted, via photocouplers PCN1, .. PCN8, and a three-state transmitter lB1, to the data bus BD of the central unit. A switch KCEN for manual coding of the card number is also connected to the BD bus via a three-state transmitter IB2.

A device DA, performing address decoding and bus synchronization, is connected to the control bus BC of the central unit and also receives at bA the predecoded address of the card under consideration. This device DA supplies to IB1 a signal vbe for validation of reading the input bits of the message and, to IB2, a signal vnc for validation of reading of the card number.

Figure 4 shows a digital output card.

The data input bus BD of the central unit is connected, on the one hand, to an 8-bit memory M, on the other hand, to a three-state transmitter IB, itself connected to a switch KCSN manual coding of the card number. A device DA, performing address decoding and bus synchronization, is connected to the control bus B c of the central unit and also receives at bA the predecoded address of the card considered. This device DA supplies the memory M with a signal md for storing the data and,
IB, a vnc validation signal for reading the card number. The signal md is also applied to a time controller device CT, itself connected to an isolator-amplifier circuit CG, the function of which will be explained below.

The memory output bits are transmitted to actuators, or other user organs, via isolator-amplifier circuits IA1 to IA8.

An analog input card will have the same configuration as that shown in Figure 3, an analog to digital converter being however additionally inserted between the sensors and the input photo-couplers.

Likewise, an analog output card will have the same configuration as that of FIG. 4, a digital-analog converter being however inserted between the outputs of the memory M and the actuators.

The installation just described is intended to transmit information from sensors and orders intended for actuators between different machines and different control cabinets or programmable logic controllers, located in different locations distant from each other, in a factory for example, and we want to be able to make it include a certain number of transceiver devices, located themselves near machines or control cabinets, and add or subtract such devices and put into service, for each from them, a greater or lesser number of cards (within the limits of their maximum capacity) without interrupting the operation of the installation. The information coming from each digital or analog input must be able to be directed to any or any digital or analog output.

The operator establishes, at a given time, by means of switches such as KCEN (FIG. 3) and KA (FIG. 2), a certain configuration of the connections to be made: it can be seen, for example, in FIG. 1, that the NC inputs -1 EN of the NA-O set will be connected to the NC-1 SN outputs of NA-1, to NA-5, while the NC-2 SN inputs of NA-O will only be connected to the NC- output 2 SN from NA, and the NC-2 EN from
NA-5 will only be connected to the NC-2 SN output of NA-O and to the NC-2 SN output of NA-1.

When the installation is switched on, the central unit of each device begins by identifying the cards which have been inserted in its own connectors, by noting their number and their nature (input or output). As the KCEN switches only provide 6 bits, while the 3-state IB transmitters generally operate on 8 bits, the two free bits will advantageously be used to indicate the nature of the card.

The program is arranged so that, during the operation of the link, each device, although receiving all the messages sent by the others, only copies, on its own output cards, messages from input cards whose number corresponds to that of one of the output cards inserted in its connectors.

The transmission of messages by successive devices NAO ... NA5 ... takes place according to a resynchronized cyclic process before each transmission of a message, as will now be explained.

Each message contains three seven-bit words, the first OXXXXXX of which indicates the number of the input card whose content is being transmitted, the second OXXXXXX contains six data bits and the third lXXXXXX contains a most significant bit which serves to recognize the last word of the message, the following two most significant bits which constitute two data bits and four least significant bits, which indicate the device number.

Transmission on the line takes place in asynchronous serial mode, with the following character format - 1 start bit - 7 data bits - 1 parity bit - 1 stop bit
Figures 5 and 6 help to understand the chronological distribution of messages. The operators have, at any time, the possibility of putting into service any of the devices. This is why it has been assumed, in the example in FIG. 5, that the NO 0, 1, 2 and 4 devices are in service, 3 not being energized, while, in the example in Figure 6, the devices O, 1, 2, 3, 5, 15 are first put into service, then the device
O is put out of service before the intervention of a new emission cycle.

On general power-up, device 0, whose central unit does not know whether or not a dialogue is already established on the line, systematically waits for a gal delay to elapse as the product of a unit delay # T by the maximum number of devices that the installation can contain (and which is
@@ dicated in the program). This unitary delay #T is provided by t: n timing device incorporated in the ES device
Successive devices are programmed to start launching a delay time N #T at the respective times 0 (device N 0), 0 + #T (device No 1), 0 + 2 #T (device no 2), etc. .If the message has for example a duration # T1 of 3.2 ms, we will take #T a little higher than this value, for example 3.6 ms. At the end of the global delay N # T, device O sends a message.

In FIG. 7, the three successive words M1 are represented,
M2, M3, of this message, which is assumed to have been requested normally, in particular by the apparatus N 1. On reception of M1, the apparatus N 1, suitably arranged to recognize this first word, activates reactivates its timing signal for a duration #T. Before the end of the interval #T, the app @@ ell @@ @ which has recognized the last word of the previous message and noted that this last word comes from the device
N 0, a @ i @ even sent a message. More precisely, this broadcast = started at the end of the previous message. Apparell @ 2, whose timeout signal has been reactivated on receipt of the first word of the message from device N 0, peas of the first word of the message from device N 1, will send its message itself before the end of this last delay #T. Ultimately, as shown in FIG. 5, during the period of sending messages and in the case of normal transmission, the messages are sent one after the other, without any isterruption, as long as the devices in service succeed one another. same without interruption in the order of increasing numbers. If there is a jump (in the example considered, direct passage from the NO 2 device to the NO 4 device) the NO 4 device, at the end of the AT delay triggered by the reception of the first word of the message sent by the NO 2 device, then did not receive any message start information from the NO 3 device. In this case, the N 4 device is arranged to reactivate a new delay signal AT and it is only at the end of this new delay that device NO 4 proceeds to send a message. In other words, this transmission occurs after the time normally reserved for the transmission of the appliance or devices which are not in use has elapsed.

It causes the following devices to be resynchronized at the start of the message sent by the NO 4 device. Whether they are in service or not, a new transmission cycle does not start until after (N-4) intervals have elapsed, equal to
AT if the corresponding device is not transmitted, and
AT1 in the event of transmission.

Also, a well-defined time interval in the cycle is reserved, at all times, for each of the N devices, whether it is in service or not. When any device is put into service, its message therefore finds its place in the time interval reserved for it, without disturbing the chronological distribution of the other messages.

In the example of FIG. 6, after a first transmission cycle in which the devices 0, 1, 2, 3, 5 and 15 are in service, it has been assumed that, at the start of the next cycle, the device O has ceased to be in service. In this case, the absence of an end of message word from the NO O device has the effect of reactivating a new delay signal.
AT of the device NO 1, which will not transmit until the end of this additional delay.

Figures 7 to 9 show the signal received by any device and the timing signal generated by this device. In the case of FIG. 7, the transmission is normal and therefore, as explained above, the first word of the received signal reactivates (or activates) the timing signal, while the last word of the signal received triggers a transmission. In the case of FIG. 8, a parasite prevents the correct reception of the first word of a message. In this case, the device behaves as if the device which should have sent this message was not in service, i.e. at the end of the period
AT counted from the start of the transmission of the previous message, a new time delay is activated, which ends with the reception of the first word of the following message.

The defective message is not taken into account.

In FIG. 9, it is assumed that the parasite intervenes at the end of the message. In this case, the device, not having identified an end of message, does not itself proceed with the transmission of a message and its timeout signal remains active until the end of the AT interval. The first word of the following message, assumed to have been received correctly, is identified as being, in the example illustrated, the second word of the previous message. It therefore does not trigger a new broadcast either. At the end of AT, a new delay time is activated. The second word of the following message obviously cannot be recognized as an end of message. On the other hand, the third word of the following message normally causes the transmission of a message by the device in question.

However, the second message is not used, since its first word has not been identified as such, and the first message is obviously not either. It is the reception of the first word of the third message which reactivates the timing signal and resynchronizes the device.

Ultimately, a perfect synchronization of the various devices is achieved, whatever the causes of disturbance and even if the message durations and the delay times are not strictly constant, and this constitutes an important advantage of the described embodiment.

The hardware and / or software implementation of the arrangements described is within the reach of those skilled in the art.

We have seen that each device, upon receiving a message, tests whether it has one or more output cards having the same numbers as the input card or cards whose numbers appear in the message and, if it is the case, send the data contained in these input cards to its own output cards of the same number. Input card data is stored in memory. State changes of at least 1 bit are sent with higher priority than cards which have not changed state. If it happens that after a given period, no entry has occurred in the memory of an exit card, this means that an incident has occurred, such as a line break for example . The CT device then sends a signal to C6 which informs the user and thus plays the role of "watchdog".

 It goes without saying that various modifications may be made to the installation described and shown, without departing from the spirit of the invention.

Claims (3)

Patent claims  1. Installation of digital transmission; per two-wire line, information provided by sensors and gold intended for actuators, comprising a two-wire transmission sign (L1L2) and a plurality of transmitter-receiver stations (NA-O ... NA-5 .. .) connected to this line and each provided with one or more parallel channels of digital (NC EN) and / or analog (NC EA) and digital (NC-SN) and / or analog (NC-SA) outputs and means (UART) for serializing the information corresponding to these channels and is characterized, in combination a) by the application, to the two-wire line, of a voltage  feed (AL) as the pieces of information  "all or nothing" provided by stations has the effect  to short circuit to define one of the two  corresponding logic levels; b) by materializing the tracks in the form of a  multiple cards (NC-1, NC-2 ...) each identified  by a binary @shade and connectable at will to each  station and by an arrangement of the installation for  authorize the commissioning at will of a number  variable of stations (NA-0, NA-1 ...) identified  each by a binary number; c) by the fact that each station comprises a unit  central unit (UC) arranged to identify the numbers of station and card numbers; d) by establishing a desired configuration which  c @@ that connections by arranging the central unit of  each station so that it constantly receives  messages, of predetermined duration, from the set  @ the other stations in service, but only operates  @ 'information from those of entry cards  who have the same identification numbers as their  own exit cards; and e) by an arrangement of the central units of the stations such  that the transmission of messages by stations in service  intervenes cyclically in the order of their  increasing identification numbers, during  successive time intervals (AT1) of each cycle  each reserved for the transmission of a message by a  well-defined station, whether it is in operation or  no and equal in number to the maximum number of stations  planned for installation.  2. Installation according to claim 1, characterized in that the central unit of each station is arranged a) to generate, from the power up of  said station, a time delay equal to  product of said maximum number of stations, by a delay  unit (AT) at least equal to said duration (AT1) of a  message b) to generate, upon receipt of information  start of message, a new unit delay of tempo  rization; c) to recognize the end of a received message and identify  the device that issued it; d) to send a message itself at the end of the message  previous when it has been correctly received and  identified as coming from the previous number station  tooth; e) otherwise, to generate, at the end of the period  referred to in (b) as many additional unit periods  that there are intermediate stations whose message has  not been issued or received correctly and to issue it  even a message at the end of these additional periods.  3. Installation according to claim 2, characterized in that each message comprises a first word containing the indication of the number of a card and a last word containing an identification bit of end of mes sage and the identification number d 'a device.