Abstract:
In present data bus systems the problem of the “babbling idiot” arises, in other words a situation wherein a terminal arbitrarily starts to transmit although a signal is already present on the bus, thus blocking the bus. According to one exemplary embodiment of the present invention, a determination as to whether the data bus is available is made within the terminal. If it has been determined that the transmitter is transmitting although the data bus is not available, a fault is present and the sender is switched off by means arranged within the terminal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to data buses in general. In particular, the present invention relates to a method for operating a terminal which receives and transmits data by way of a bus line, a terminal for connection to a bus line, and a data bus system comprising a bus line and a terminal.  
         [0002]     In applications such as in the automotive industry or in aircraft construction, these days it is increasingly common to use bus systems instead of complicated cable harness systems. This makes for easier maintainability of the system and also for a reduction both in cabling expenditure and weight. In this, in particular the automotive industry has reached an agreement in relation to a common bus standard, namely the CAN bus system according to DIN ISO 11898. In aircraft construction there are for example the ARINC 629 standard and the MIL-SDT 1553 standard. In particular in applications related to the construction of aircraft it is imperative that the bus system is very robust as far as faults are concerned. At the heart of this issue is the prevention of any breakdown in communication as a result of malfunction of an individual control device or terminal.  
         [0003]     In these data bus systems it can indeed happen that a defective device or terminal interferes with the entire bus. The so-called “babbling idiot”, i.e. a device or terminal which continuously writes nonsensical information to the bus, is a typical example of this. In extreme cases this leads to a situation where communication between the other devices/terminals that are connected to the same bus line is no longer possible at all.  
         [0004]     Up to now, this has been able to be prevented or brought to an end by external measures only inadequately, in that the individual transmitters have been monitored by external means, and have been switched off from the outside when a “babbling idiot” occurred. This results in increased linking effort and in addition in increased expenditure.  
       SUMMARY OF THE INVENTION  
       [0005]     According to an exemplary embodiment of the present invention, a method for operating a terminal is provided which receives and transmits data by way of a bus line. The bus line is monitored to determine whether the bus line is busy, i.e. whether data is being transported by way of the bus line. Furthermore, it is determined whether, at the particular time, the corresponding terminal is transmitting data to the bus line. According to the method, the data transmission from the terminal to the bus line is prevented if it has been determined that the terminal is transmitting data to the bus line, and the bus line is busy.  
         [0006]     In other words, according to this exemplary embodiment of the present invention any data transmission from the terminal to the bus line may be prevented, or the terminal may be blocked or switched off if the terminal is transmitting although the bus is not available.  
         [0007]     It is believed that this makes it possible to switch off or prevent any data transmission from a terminal if said terminal turns out to be a “babbling idiot”, i.e. if this said terminal sends data to the bus line despite the bus line being busy.  
         [0008]     According to a further exemplary embodiment of the present invention, a terminal for connection to a bus line is specified in order to receive and transmit data by way of the bus line. The tennis comprises a monitoring circuit for monitoring the bus line in order to determine whether the bus line is busy. Furthermore, the terminal comprises a transmission determination circuit for determining whether the terminal is sending data to the bus line, as well as a transmission prevention circuit for preventing data transmission to the bus line if it has been determined that the terminal is sending data to the bus line although the bus line is busy.  
         [0009]     According to this exemplary embodiment of the present invention, a terminal is disclosed which may interrupt data transmission to the bus line entirely without external supervision, i.e. entirely of its own accord, as soon as it has been determined that such data transmission is unjustified. It is believed that thus any faulty behaviour of the transmitter or of the terminal may be detected and prevented at a higher degree of safety than is known from the state of the art.  
         [0010]     According to a further exemplary embodiment of the present invention, a data bus system is disclosed which comprises a bus line and a terminal. In this data bus system the terminal comprises a monitoring circuit, a transmission determination circuit and a transmission prevention circuit such that transmit and receive lines of the terminal are monitored and as soon as an unjustified transmission from the terminal or from a transmitter of the terminal is registered, transmission of the data is prevented. Unjustified transmission is for example determined in that the transmitter or the terminal attempts to place data in the data line although said data line is either not available or is busy.  
         [0011]     According to another exemplary embodiment of the present invention that both lines of the terminal, i.e. the transmit line and the receive line, are monitored, and when any unjustified transmission on the transmit line is determined, i.e. if the transmitter transmits although the bus is not available, it is determined that a fault has occurred, and the transmitter is switched off. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Below, exemplary embodiments of the present invention are described with reference to the accompanying figures.  
         [0013]      FIG. 1  is a flow chart of an exemplary embodiment of a method for operating a terminal in a bus system according to the present invention;  
         [0014]      FIG. 2  is a simplified block diagram of a first exemplary embodiment of a data bus system comprising a first exemplary embodiment of a terminal according to the present invention; and  
         [0015]      FIG. 3  is a simplified block diagram of a second exemplary embodiment of a data bus system comprising a second exemplary embodiment of a terminal according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  is a simplified flow chart of an exemplary embodiment of a method for operating a terminal which receives and transmits data by way of a bus line.  
         [0017]     As shown in  FIG. 1 , after the start in step S 1 , in Step S 2  it is determined whether or not the bus, i.e. the bus line, is occupied. If in step S 2  it is determined that the bus line is occupied, operation progresses to step S 3  in which it is determined whether or not the transmitter of the terminal is transmitting. If in step S 3  it is determined that the transmitter is transmitting, operation progresses to step S 4  in which subsequently the presence of a fault is determined, and the transmitter is switched off. From step S 4  operation progresses to step S 5  where operation stops.  
         [0018]     If in step S 2  it is determined that the bus is not occupied, the process reverses recursively. If in step S 3  it is determined that the transmitter is not transmitting, operation reverses recursively to step S 2 .  
         [0019]     The method shown in  FIG. 1  can for example be carried out such that a transmit line and a receive line from and to a terminal connected to a bus line are monitored, and any data transmission of the terminal is interrupted if it has been determined that there is data traffic both on the receive line and on the transmit line. Non-identical data traffic on the receive line and on the transmit line means that the data on the transmit line differs from the data on the receive line.  
         [0020]     Advantageously, the process steps shown in  FIG. 1  are carried out in the respective terminal which is connected to the bus line. In this way, no external supervision is required. This also provides great flexibility to the bus system because for example if new terminals are added, no external control or coordination system needs to be adapted. Furthermore, this increases the robustness of the bus system as far as faults are concerned.  
         [0021]      FIG. 2  shows a simplified block diagram of a first exemplary embodiment of a data bus system with a first exemplary embodiment of a terminal according to the present invention.  
         [0022]     As shown in  FIG. 2 , the bus system comprises a data bus  2  with two data lines  4  and  6 , each of which is connected to the terminal  12  by way of respective tap lines  8  and  10 . In particular, the data lines  4  and  6  are connected to a directional coupler  14  in terminal  12  by way of the tap lines  8  and  10 . Apart from the directional coupler  14 , the terminal  12  comprises a receiver  22 , a transmitter  24 , two carrier-sense circuits  26  and  28 , a comparator  30 , as well as an AND-gate  32 , whose output is connected to the transmitter as a “transmit disable”.  
         [0023]     The directional coupler  14  is connected to the transmitter  24  by way of transmit lines T X    18  and  20 . Furthermore, the directional coupler  14  is connected to the receiver  22  by way of receive lines R x    14  and  16 . The receive lines R X    14  and  16  are also input signals for the carrier-sense circuit  26  and the comparator  30 . The transmit lines T x    18  and  20  are also input signals for the carrier-sense circuit  28  and the comparator  30 . The outputs of the carrier-sense circuits  26  and  28  and of the comparator  30  form the inputs of the AND-gate  32 .  
         [0024]     The function of the terminal circuit shown in  FIG. 2  is as follows: when a signal is present on the data bus  2 , the directional coupler  14  distributes said signal to the transmit lines T x  and the receive lines R x . T X  and R X  are monitored by way of signal measuring by the carrier-sense circuits  26  and  28 . The carrier-sense circuits  26  and  28  generate an output signal if a signal voltage is correspondingly present on T X  or R X . At the same time the signal content of T X  and R X  is compared by means of the comparator  30 . The comparator  30  generates an output signal only if the contents of the input signals, i.e. of T X  and R X , are not identical.  
         [0025]     If the transmitter  24  during a transmission to the data bus  2  arbitrarily starts data transmission by way of the data bus  2 , the following conditions have been met:  
         [0026]     1. On the T X -line a signal is detected, whereupon the carrier-sense circuit  28  generates an output signal.  
         [0027]     2. On the R X -circuit a signal is detected, whereupon the carrier-sense circuit  26  generates an output signal.  
         [0028]     3. The comparator detects that the transmit signal (on T X ; i.e. on the lines  18  and  20 ) is not equal to the receive signal (R X , i.e. on the lines  14  and  16 ) and subsequently generates an output signal.  
         [0029]     These three conditions 1 to 3 are then linked by way of the AND-gate which then by way of “transmit disable” switches the transmitter off. In this way a logic is provided within the terminal  12 , which logic suppresses or prevents unjustified transmitting by the transmitter  24 . In this way terminal  12  is prevented from developing into a “babbling idiot”.  
         [0030]      FIG. 3  shows a simplified block diagram of a second embodiment of a data bus system with a second embodiment of a terminal according to the present invention. For identical or corresponding elements, identical reference numbers are used in  FIGS. 2 and 3 .  
         [0031]     The data bus  2  in  FIG. 3  is an optical waveguide. Accordingly, the data transmission system shown in  FIG. 3  is an optical data transmission system. Since the elements  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30  and  32  have already been described in the context of  FIG. 2 , reference is made to that description. The function of these elements in the exemplary embodiment shown in  FIG. 3  corresponds to the function of these elements in the exemplary embodiment shown in  FIG. 2 .  
         [0032]     In a way that is different from  FIG. 3 , the optical signals from the data bus  2  are decoupled from the optical waveguide by means of fork couplers  40  and  42 , and are forwarded by way of a cross coupler  44  to an electro-optical transducer  46  on the transmitter side, and to an opto-electrical transducer  48  on the receiver side. The electro-optical transducers  46  and  48  transduce the electrical signals which are received or transmitted by the terminal into optical signals, which are then coupled into the optical waveguide by way of the cross coupler  44  and the fork couplers  40  and  42 . Likewise, the electro-optical transducers  46  and  48  transduce the optical signals which are decoupled from the optical waveguide by the fork couplers  40  and  42  and the cross coupler  44  into electrical signals which form the transmit signal T X  on the lines  18  and  20 , and the receive signal of R X  on the lines  14  and  16 .  
         [0033]     As already mentioned according to the present invention any faulty behaviour of the transmitter is detected within the terminal with a very high probability, and is also prevented. In this way there is no need to provide any external control or monitoring system which for example switches off a transmitter that changes into a “babbling idiot”. In this way, blocking of the network is prevented.  
         [0034]     It should be noted that the term “comprising” does not exclude other elements or steps and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined.  
         [0035]     It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.