Abstract:
The invention relates to a communication station (S 32 -S 34 ), which as a passive station in a communication system which is not authorized to transmit but listens in on all communication processes and can receive only data (D) actually intended for it, which fact can be conclusively verified by means of a destination point code (T) assigned to the data (D). According to the invention, said communication station is additionally upgraded to receive data (D), the destination (T) and originating point code (S) of which matches an entry (FT, FS) in a filter table (F) provided for in a communication station (S 32 -S 34 ) which has been upgraded in accordance with the invention.

Description:
DESCRIPTION  
         [0001]    Communication systems, such as the Profibus, as is described in DIN Standards 19245 Part 1 and 19245 Part 2 and in the document by Peter Neumann: Kommunikationssysteme in der Automatisierungstechnik, [Communication systems in automation engineering], Verlag Technik, Berlin, are used to provide the information interchange between various subsystems in a technical installation.  
           [0002]    One special feature in this context is real-time data interchange as is required, for example, for process monitoring or for automatic control of technical systems. Profibus (Process Field Bus) is a standardization method that is used by automation companies and scientific organizations in the Federal Republic of Germany.  
           [0003]    Profibus is a fieldbus system and is thus used, in the narrow sense, for standardized connection of automation devices in the field area.  
           [0004]    The areas in which Profibus is used include, for example, autonomous use as a process data bus system for automation projects or as a subordinate communication level in process control systems. The communication or bus subscribers may thus equally well be programmable logic controllers or control systems, numeric controllers or control systems, a local automation device or sensors and/or actuators with bus interfaces.  
           [0005]    Each bus subscriber is a terminal of the communication system. As such, it has a communication means which allows the subscriber to be connected to the communication system, the bus. The communication means, which may have its own processor or a so-called ASIC, controls the transmission processes essentially independently of the other subscriber actions.  
           [0006]    The data interchange between the communication means and the terminal takes place, for example, by virtue of the fact that part of the memory in the terminal is mapped, virtually as a “window” across to the memory provided in the communication means. This method is called shared memory or memory mapped I/O. Data from the bus are buffered in the storage area provided for this purpose in the communication means. The terminal&#39;s control unit can then read the data directly from the communication means as if said data were already stored in its own main memory.  
           [0007]    For Profibus, a distinction is drawn between a physical topology and a logic topology. The physical topology is defined essentially by a line interface in accordance with RS-485. In consequence, the Profibus is a serial bus. In contrast, the logic topology corresponds on the one hand to specific bus subscribers being linked in a ring, these subscribers being called active subscribers in the following text, and on the other hand to in each case one active subscriber being linked in the form of a star to the other bus subscribers which are not included in this linking in the form of a ring, and which are called passive subscribers in the following text.  
           [0008]    The authorization for bus access among the active bus subscribers is allocated in accordance with an identification method, the commonest method being the token ring method, which is known per se. The token, a specific bit pattern which acts as an identification, is passed on from one active subscriber to the next active subscriber corresponding to the logic linking in the form of a ring. The active subscriber which has the token internally has access authorization to the medium, this authorization allowing access to the bus either for a limited time or for a fixed number of transmission processes.  
           [0009]    Logic linking in the form of a star exists between in each case one active subscriber and one or more passive subscribers. The active subscriber in such a link in the form of a star is called the master in the following text. Data are retrieved from the passive bus subscribers by means of a global function which is implemented in the respective active subscriber. This retrieval is called polling in the following text. A passive subscriber may not access the medium (transmit data) until it is granted “permission” (polling) by the respective active subscriber.  
           [0010]    A disadvantage of the communication method which has been known until now from the prior art is that it is impossible for passive communication subscribers which do not have their own transmission authorization to interchange data directly.  
           [0011]    In consequence, the object of the present invention is to specify a passive communication subscriber which is provided with the capability to receive directly a data item transmission via the bus from another passive communication subscriber.  
           [0012]    The object is achieved by a listening communication subscriber (S32-S34) for connection to a bus system (B) for industrial control systems, in particular a bus system (B) with programmable logic controllers,  
           [0013]    a data item which is to be transmitted via the bus having at least one destination identifier and one source identifier,  
           [0014]    the listening communication subscriber having its own identifier,  
           [0015]    a filter table having at least one entry in each case having at least two parameters being provided for the listening communication subscriber,  
           [0016]    the first parameter representing a destination identifier,  
           [0017]    the second parameter representing a source identifier,  
           [0018]    the listening communication subscriber in each case receiving a data item on the one hand when the destination identifier of the data item matches with its own identifier and  
           [0019]    the listening communication subscriber in each case, on the other hand, receiving a data item when the destination identifier and the source identifier of the data item match the corresponding parameters of an entry in the filter table.  
           [0020]    According to an advantageous refinement, the listening communication subscriber is provided with a buffer storage area in which a received data item can be buffered and from which the data item can be transferred to an input storage area as soon as it is found that the received data item is intended for the respective listening communication subscriber. This allows the data transmitted via the bus to be stored temporarily with the capability to evaluate the destination and source identifiers of the received data item within the buffer storage area, so that only one data item, which is actually intended for the respective listening communication subscriber, is transferred to its input memory area so that, in consequence, the processing and evaluation of the wanted data in the received data item are not influenced by the configuration according to the invention of the listening communication subscriber.  
           [0021]    A further object of the present invention is to specify a communication system in which a data item which has been transmitted via the bus by a first passive communication subscriber can be received directly by another passive communication subscriber.  
           [0022]    The object is achieved in that, in a communication system which is formed by a bus system for industrial control systems, in particular a bus system having programmable logic controllers, and has active communication subscribers and passive communication subscribers, at least one of the passive communication subscribers is a listening communication subscriber,  
           [0023]    a data item which is to be transmitted via the bus having at least one destination identifier and one source identifier,  
           [0024]    the listening communication subscriber (S 32 -S 34 ) having its own identifier (K),  
           [0025]    a filter table having at least one entry in each case having at least two parameters being provided for the listening subscriber,  
           [0026]    the first parameter representing a destination identifier,  
           [0027]    the second parameter representing a source identifier,  
           [0028]    the listening communication subscriber in each case receiving a data item on the one hand when the destination identifier of the data item matches with its own identifier, and  
           [0029]    the listening communication subscriber in each case, on the other hand, receiving a data item when the destination identifier and the source identifier of the data item match the corresponding parameters of an entry in the filter table.  
           [0030]    In a communication system having active communication subscribers and passive communication subscribers and which is formed by a bus system for industrial control systems, in particular a bus system having programmable logic controllers, the listening communication subscriber according to the invention can be used advantageously since a listening communication subscriber designed according to the invention can handle the communication processes within the communication system more effectively.  
           [0031]    In an advantageous refinement of the communication system, the listening communication subscriber is distinguished by the fact that it is provided with a buffer storage area in which a received data item can be buffered and from which the data item can be transferred to an input storage area as soon as it is found that the received data item is intended for the respective listening communication subscriber. The advantages which have been quoted in this context for the individual communication subscriber configured according to the invention also apply analogously to the communication system in which the communication subscriber is used.  
           [0032]    A further object of the present invention is to specify a communication method which allows at least direct communication between passive communication subscribers.  
           [0033]    The object is achieved by a communication method for a listening communication subscriber (S 32 -S 34 ) for connection to a bus system (B) for industrial control systems, in particular a bus system (B) with programmable logic controllers, a data item (D) which is to be transmitted via the bus (B) having at least one destination identifier (T) and one source identifier (S), the listening communication subscriber (S 32 -S 34 ) having its own identifier (K), and a filter table (F) having at least one entry in each case having at least two parameters (FT x , FS x ) being provided for the listening communication subscriber (S 32 -S 34 ), the first parameter (FT x ) representing a destination identifier (T) and the second parameter (FS x ) representing a source identifier (S), and the method comprising at least the following steps:  
           [0034]    the listening communication subscriber (S 32 -S 34 ) in each case receives a data item (D) on the one hand when the destination identifier (T) of the data item (D) matches its own identifier (K), and  
           [0035]    the listening communication subscriber (S 32 -S 34 ) in each case receives a data item (D) on the other hand when the destination identifier (T) and the source identifier (S) of the data item (D) match the corresponding parameters (FT x , FS x ) of an entry in the filter table (F).  
           [0036]    In an advantageous refinement of the communication method, a buffer storage area is provided in which a received data item is buffered and from which the data item is transferred to an input storage area as soon as it is found that the received data item is intended for the respective listening communication subscriber. The advantages which have been quoted in this context for the individual communication subscriber configured according to the invention also apply analogously to the communication method.  
           [0037]    The solutions and their refinements according to the invention can advantageously be used with a serial bus, in particular the Profibus, as the bus system. A serial bus allows interference-free data transmission even over long distances and is thus particularly suitable for use in industrial environments. The Profibus has been proven for use in automation projects and, in consequence, is in widespread use. 
       
    
    
       [0038]    Other advantages and details according to the invention result from the following description of an exemplary embodiment in conjunction with the subclaims and with reference to the figures in which, in detail:  
         [0039]    [0039]FIG. 1 shows a bus subscriber and communication system (bus) for Profibus,  
         [0040]    [0040]FIG. 2 shows the layout of a data item to be overtopped via the bus,  
         [0041]    [0041]FIG. 3 shows bus subscribers which have been given the capability to carry out the method according to the invention, and  
         [0042]    [0042]FIG. 4 shows subscribers to an exemplary communication process according to the invention. 
     
    
       [0043]    According to FIG. 1, a plurality of active subscribers M 1 , M 2  and passive subscribers S 32 , S 33 , S 34  are connected to a line bus B. The bus protocol is assumed to be Profibus-DP. The subscribers M 1 , M 2 , S 32 -S 34  are assumed to be automation devices for controlling and/or monitoring a technical process. The active subscribers M 1 , M 2  are assumed to be central processors in a programmable logic control system (PLC). The passive subscribers S 32 -S 34  are assumed to be sensors or actuators and/or local automation devices with bus interfaces, for example for outputting or receiving status information relating to the technical process. The technical process is essentially monitored and controlled by the control program predetermined by the active subscribers M 1 , M 2 . In particular, the respective structure of the control program governs the nature and direction of the data flow via the bus.  
         [0044]    The prior art does not envisage direct communication between the passive subscribers S 32 -S 34 ; instead of this, communications are envisaged in which the active subscriber M 1 , M 2  retrieves data from the respective passive subscriber S 32 -S 34  or transmits data to the respective passive subscriber S 32 -S 34 .  
         [0045]    If, nevertheless, data which are available in the region of a first passive subscriber, for example S 33 , are intended to be transferred to a second passive subscriber, for example S 32 , then this is done by including at least one active bus subscriber, for example M 1 .  
         [0046]    By way of example, the following text describes a communication process in which a data item D which is available in the region of a first passive bus sub-scriber S 33  is intended to be transmitted to a second bus subscriber S 32 . Unless specifically mentioned to the contrary, the further explanation of an exemplary embodiment of the invention always refers back to this constellation.  
         [0047]    The active bus subscriber retrieves a data item D, for example a data record or an input value, from the passive bus subscriber S 33 . To do this, the active bus subscriber M 1  sends to the passive bus subscriber S 33  a specific data item D which causes the latter to transmit the data item D to be transmitted to the active bus subscriber M 1 .  
         [0048]    Each data item D to be transmitted is—in accordance with the bus protocol specifications—supplemented at least by information about the receiver (the destination identifier T) and the sender (the source identifier S). In consequence, a data item D comprises at least the destination identifier T, the source identifier S and the actual wanted data N. FIG. 2 shows an illustration by way of example of the structure of the data item resulting from this. The addressee of a data item D can be identified uniquely by the destination identifier T. In the present case, the addressee is thus the active subscriber M 1 , which receives the data item D and can thus evaluate it.  
         [0049]    The control program predetermined by the active subscriber M 1  defines—independently of the specific communication process—the processing and handling of the wanted data N in the received data item D. In the context of the chosen example of a communication process, the intention is to transfer the wanted data N to the passive subscriber S 32 . A data item D which is transmitted to the passive subscriber S 32  is thus generated in the region of the active subscriber M 1 . In this way, the message sent by the slave S 33  finally arrives at the slave S 32 .  
         [0050]    The physical transmission of the data is known per se. In order to organize the data transmission, at least one input area E and at least one output area A are provided in each case for each bus subscriber M 1 , M 2 , S 32 -S 34 , that is to say for both the active and passive bus subscribers, as illustrated in FIG. 1.  
         [0051]    A data item D to be transmitted is in each case stored in the output area A of the respective bus subscriber M 1 , M 2 , S 32 -S 34 , and can thus be transmitted via the bus B. At the receiver M 1 , M 2 , S 32 -S 34  of the transmitted data item D, the data item D is transferred to the receiver&#39;s input area E.  
         [0052]    As soon as the receiver M 1 , M 2 , S 32 -S 34  registers the presence of the data item D in its input area E, the received data item D can be evaluated. The evaluation relates at least to the destination identifier T contained in the data item D. If the destination identifier T matches the respective identifier of the receiver, then the data item has arrived at its destination address.  
         [0053]    This explains the communication principle, which is known from the prior art, between passive bus subscribers S 32 -S 34  which do not have any transmission authorization. The messages between two passive bus subscribers, for example S 32  and S 33 , are always diverted via an active bus subscriber M 1 .  
         [0054]    For communication processes between passive bus subscribers S 32 -S 34 , the present invention avoids the disadvantageous diversion via an active bus subscriber M 1 , M 2 .  
         [0055]    To this end, a passive bus subscriber S 32 -S 34  is given the capability to “eavesdrop” on the transmissions taking place via the bus B. As a result of this eavesdropping, it is possible for a passive bus subscriber S 32 -S 34 —for example the slave S 32 —to receive the respective data item D currently being transmitted via the bus B, irrespective of whether this data item is intended for it.  
         [0056]    The communication means KM provided for each bus subscriber M 1 , M 2 , S 32 -S 34  and for the respective interface I still monitors the transmissions via the bus for the communication process described further above, but is designed such that only one data item D, whose destination identifier T matches the identifier of the respective bus subscriber, is received.  
         [0057]    According to the present invention, the communication means KM is, in contrast, refined in such a manner that it is able to receive every data item D which is transmitted via the bus B. This allows efficient communication between passive bus subscribers S 32 -S 34 , and this will be described in the following text with reference to FIG. 3 and FIG. 4.  
         [0058]    A data item D which is intended to be transmitted from the slave S 33  to the slave S 32  is first of all transmitted to an active subscriber M 1 , M 2 —for example the master M 1 . The data item D is in this case supplemented at least by the destination identifier T of the recipient, in this case, that is to say, that of the master M 1 , and the source identifier S of the sender, in this case that is to say that of the passive subscriber S 33 .  
         [0059]    The passive bus subscribers S 32 -S 34  now eavesdrop on the transmission and, in the process, transfer the data item D to a buffer storage area P (FIG. 3).  
         [0060]    As soon as a passive bus subscriber S 32 -S 34  registers the presence of a data item D in its buffer storage area P, the data item can be evaluated. This evaluation, in the case of the communication method according to the invention and in the case of the communication  
         [0061]    subscriber S 32 -S 34  which has been given the capability according to the invention, relates to the destination identifier T and to the source identifier S of the data item D.  
         [0062]    According to the invention, a filter table F can be defined in advance for the respective passive bus subscriber S 32 -S 34 , in order to evaluate the destination identifier T and the source identifier S of a data item D (FIG. 4). Each entry in this filter table F has at least two parameters FT, FS, the two parameters designating the address of a communication subscriber, the first parameter FT, for example, designating the recipient M 1 , M 2 , S 32 -S 34  of a data item D, and the second parameter FS designating the sender M 1 , M 2 , S 32 -S 34  of a data item D.  
         [0063]    The number n of entries in the filter table F is essentially limited only by the storage area  
         [0064]    available for the filter table F. The resulting filter table entries are thus FT 1 , FS 1 -FT n , FS n .  
         [0065]    To evaluate the data item D present in the buffer storage area P, the respective passive bus subscriber S 32 -S 34  compares the destination identifier T and the source identifier S of the data item D with the respective filter table entries FT 1 ,FS 1 -FT n ,FS n . If one FT x ,FS x  of the filter table entries FT 1 ,FS 1 -FT n ,FS n  matches the destination identifier T and the source identifier S of the evaluated data item D, then the respective passive bus subscriber S 32 -S 34 , in the case of the communication described by way of example for the passive bus subscriber S 32 , has found that the data item D is intended for it.  
         [0066]    Once the respective passive bus subscriber S 32 -S 34  has found that the data item D is intended for it, it transfers the data item D from the buffer storage area P to its input area E (FIG. 3).  
         [0067]    Once the data item D is present in the input area E of the recipient S 32 , the evaluation and processing of the wanted data N in the data item D start in the manner known per se. The other bus subscribers, for which the data item D was not intended, reject the contents of their buffer storage areas P or do not evaluate the contents.  
         [0068]    The entries FT 1 ,FS 1 -FT n ,FS n  in the filter table F are obtained in the course of design of the technical installation in which the communication system, with the bus subscribers S 32 -S 34  refined according to the invention, is used.  
         [0069]    The filter table thus represents the interdependences between the respective bus  
         [0070]    subscribers. If, for example, the passive bus subscribers S 33  and S 34  are sensors or local automation devices for receiving status information about a technical process TP to be controlled or to be monitored, whose status information is required by another local automation device, for example the passive bus subscriber S 32 , for example for controlling a specific technical apparatus in the process TP, then the design (which was outlined briefly above) of the technical installation ensures that the data delivered by the bus subscriber S 33  are evaluated at least by the bus subscriber S 32 . If the communication system of the specific technical installation has at least one active bus subscriber M 1 , then, in consequence, the filter table F in the passive bus subscriber S 32  contains at least the entry FT x =M 1 , FS x =S 33 .  
         [0071]    The filter table F can either be defined in a fixed manner in advance for the respective bus subscribers S 32 -S 34  in the course of commissioning the communication system, or else it can be varied retrospectively via a user interface, for example via a coding switch or a keyboard.  
         [0072]    The communication relationship made possible by the invention can also be used advantageously for the situation of data transmission from an active subscriber M 1 , M 2 , in this case the master M 1 , to a passive subscriber S 32 -S 34 , in this case the passive subscriber S 32 .  
         [0073]    In the case of data transmission from the active subscriber M 1  to the passive subscriber S 32 , the data item D is supplemented at least by the destination identifier T (T=S 32 ) and the source identifier S (S=M 1 ). The data item D would contain, for example, wanted data N which are intended to be transmitted to all the passive subscribers S 32 -S 34  in order to react to an alarm situation. In the case of the data transmission known from the prior art, the master M 1  transmits one and the same data item D with a respectively adapted destination identifier T sequentially and successively to all the passive subscribers S 32 -S 34  involved. In the case of the data transmission which is made possible by the invention, the master M 1  transmits the data item D only to one passive subscriber S 32 , the other passive subscribers S 33 -S 34  receiving the same data item D at the same time as the actual addressee, the subscriber S 32 , provided that their filter tables F contain the entry FT x =S 32 , FS x =M 1 .  
         [0074]    This communication relationship is advantageous since the active subscriber M 1  has to initiate the transmission of the data item D only once, so that the initiation of the other transmission processes otherwise required is avoided, so that the active subscriber M 1  is relieved of the load of communication processes, and the computation time saved is thus available for other purposes.  
         [0075]    This communication relationship is furthermore advantageous since both the actual addressee, the passive subscriber S 32 , and the other passive subscribers S 33 -S 34  with corresponding entries FT x , FS x  in the filter table F receive the data item D at the same time. It is thus possible, for example, to synchronize the passive subscribers S 32 , S 33  and S 34 . In addition, it is possible to ensure that any alarm action is carried out at the same time by the passive subscribers S 32 -S 34 , which would not be possible with the communication known from the prior art, in which the active subscriber M 1  transmits the data item D sequentially to all the passive subscribers S 32 -S 34 .  
         [0076]    In summary, the invention can be described in brief as follows: a communication subscriber S 32 -S 34  which, as a passive subscriber of a communication system, does not have its own transmission authorization but eavesdrops on all the communication processes can, however, according to the prior art receive only those data items D which are also intended for it, which can be identified without doubt from a destination identifier T allocated to the data items D, is given the capability, according to the invention, also to receive those data items D whose destination identifier T and source identifier S match an entry FT, FS in the filter table F provided in the communication subscriber S 32 -S 34  which has been given the capability according to the invention. In this way and in an advantageous manner, on the one hand direct communication is possible between passive communication subscribers S 32 -S 34  and, on the other hand, it is possible for an active and/or passive transmitter M 1 , M 2 , S 32 -S 34  to communicate at the same time with a number of passive communication subscribers S 32 -S 34  which have been given the capability according to the invention.