Patent Publication Number: US-2022239527-A1

Title: Device for a subscriber station of a serial bus system and method for communication in a serial bus system

Description:
FIELD 
     The present invention relates to a device for a subscriber station of a serial bus system and to a method for communication in a serial bus system which operates at a high data rate and with great fault robustness. 
     BACKGROUND INFORMATION 
     At present, bus systems are frequently used in the communication between sensors and control units. Especially in vehicles, a bus system is often used in which data are transmitted as messages based on the ISO 11898-1:2015 standard as a protocol specification using CAN FD. The messages are transmitted between the bus subscribers of the bus system, e.g., a sensor, control unit, transmitter, and others. 
     It is frequently desired that technical systems offer more and more functions. This applies especially to vehicles. The increasing number of functions also causes an increase in the data traffic on the bus system. In addition, it is also often required that the data be transmitted from the transmitter to the receiver more rapidly than at present. As a consequence, there will be a further increase in the desired bandwidth of the bus system. 
     In order to allow for a transmission of data at a higher bit rate than in CAN, the CAN FD message format provided an option for switching to a higher bit rate within a message. In such techniques, the maximally possible data rate is increased beyond a value of 1 MBit/s through the use of a higher clock rate in the area of the data fields. Hereinafter, such messages are also referred to as CAN FD frames or CAN FD messages. In CAN FD, the useful data length is expanded from 8 to up to 64 bytes and the data transmission rates are considerably higher than in CAN. 
     For instance, one advantage of a CAN- or CAN FD-based communications network is its robustness with regard to errors. The communications network is furthermore able to react rapidly to changing operating states. This is of importance in particular in a vehicle so that the function of safety systems is rapidly implementable should the need arise. 
     However, such a network still has a considerably lower speed than a data transmission in a 100 base T1 ethernet, for example. In addition, the useful data length of up to 64 bytes currently achieved by CAN FD is too low for some applications. 
     SUMMARY 
     Therefore, it is an object of the present invention to provide a device for a subscriber station of a serial bus system and a method for communication in a serial bus system which solve the aforementioned problems. More specifically, a device for a subscriber station of a serial bus system and a method for communication in a serial bus system will be provided in which a high data rate and an increase in the amount of useful data per frame are able to be realized with great flexibility in the operation of a technical system using the bus system for the communication, and with a great error robustness of the communication. 
     The object may be achieved by a device for a subscriber station of a serial bus system in accordance with the present invention. 
     In accordance with an example embodiment of the present invention, the device has a transmit signal analysis module for counting edges of a transmit signal that is to be transmitted on a bus of the bus system in order to exchange a message between subscriber stations of the bus system; a receive signal analysis module for counting edges of a receive signal that is generated from a signal transmitted on the bus because of the transmit signal, in which the bus states of the signal for the message in a first communications phase differ from bus states of the signal received in a second communications phase; and an evaluation module for evaluating the difference that results from a comparison of the edges counted by the transmit signal analysis module and the edges counted by the receive signal analysis module, and in the event that the signal propagation time on the bus is greater than the bit time of the receive signal, the evaluation module is developed to signal whether the amount of the difference is less than or equal to a predefined value or whether the amount of the difference is greater than the predefined value, the predefined value being greater than zero. 
     The device makes it possible to detect a transmission conflict in the bus system without any special effort. The device is able to detect whether another subscriber or its transceiver simultaneously drives another bus state by its own subscriber station or its transceiver, that is to say, whether a conflict exists. In this way the advantages of CAN bus systems may be retained even when using such high bit rates at which the signal propagation time of the transmit signal TxD to the receive signal RxD is considerably greater than the length of a bit. 
     In the process, the device uses only two counters, which are clocked with the receive message Rx and the transmit message Tx and compared to each other in order to detect a transmission conflict on the bus. In this way, no direct comparison of the instantaneous values of receive message Rx and transmit message Tx is required. Such a direct comparison would require a measurement of the signal propagation time and the intermediate storage of a sequence of the last values of transmit message Tx for the evaluation by a protocol control unit and would therefore be quite complex. 
     Because of the embodiment of the device of the present invention, a transmission conflict is detectable even if both bus states are actively driven in one frame in the data phase. This also applies if a superposition of driven signals occurs on the bus so that “analog” levels come about on the bus and a transmission conflict is no longer reliably detectable by comparing transmit signal TXD and receive signal RXD because the resulting receive signal RXD is no longer accurately predictable. Because of the described device, an evaluation by a microcontroller or a protocol control unit in the device and/or by the communications control device may therefore be omitted. 
     The development of the device makes it possible for each subscriber station of the bus system to interfere with or interrupt the transmission of any other subscriber station by an error frame, if necessary. From the user standpoint, this is very advantageous because it can save time in an error case in that a currently transmitted message is aborted and other information is then able to be transmitted on the bus. This is very useful in particular with frames that are longer than a CAN FD frame having 64 bytes in the data phase, especially with frames that are to include 2-4 Kbytes or more. 
     As a result, the use of the device, which particularly is a transceiver, makes it possible to ensure the receiving of the frames with great flexibility with regard to current events in the operation of the bus system and at a low error rate even if the number of useful data per frame is increased. It is therefore also possible to communicate with great error robustness in the serial bus system even at a high data rate and an increase in the number of useful data per frame. 
     Thus, with the device in the bus system, it is particularly possible to retain an arbitration from CAN in a first communications phase and still considerably increase the transmission rate yet again in comparison with CAN or CAN FD. 
     This contributes to a realization of a net data rate of at least 10 Mbits per second. In addition, the size of the useful data per frame may be up to 4096 bytes or more. 
     In accordance with an example embodiment of the present invention, the method carried out by the device may also be used when at least one CAN FD-tolerant subscriber station, which is equipped according to the ISO 11898-1:2015 standard, is provided on the bus system, and/or at least one CAN FD subscriber station which transmits messages according to the CAN protocol and/or the CAN FD protocol. 
     Advantageous further embodiments of the device of the present invention are disclosed herein. 
     According to one exemplary embodiment of the present invention, the transmit signal analysis module has a counter for counting falling edges of the transmit signal, and the receive signal analysis module has a counter for counting falling edges of the receive signal. 
     According to another exemplary embodiment of the present invention, the transmit signal analysis module has a first counter for counting falling edges of the transmit signal and a second counter for counting rising edges of the transmit signal, and the receive signal evaluation module has a first counter for counting falling edges of the receive signal and a second counter for counting rising edges of the receive signal, the evaluation module being developed to evaluate the difference that results from a comparison of the edges counted by the first counters and to evaluate the difference that results from a comparison of the edges counted by the second counters. 
     According to one special embodiment variant of the present invention, in the event that the signal propagation time on the bus is lower than or equal to the bit time of the receive signal, the evaluation module is developed to signal whether the amount of the difference is equal to zero or whether the amount of the difference is greater than zero. 
     The evaluation module may possibly be developed to carry out the evaluation after the count value has been incremented by the receive signal analysis module, the evaluation module being developed to output the signaling of the evaluation at the connection of the device at which the receive signal is to be output from the device. 
     The transmit signal analysis module may be developed to use the transmit signal as a clock for the counting and to filter out overshoots at the edges of the transmit signal. In addition or as an alternative, the receive signal analysis module may be developed to use the receive signal as a clock for the counting and to filter out overshoots at the edges of the receive signal. 
     According to one special embodiment variant of the present invention, the bus states of the signal received from the bus in the first communications phase are generated by a different physical layer than the bus states of the signal received in the second communications phase. 
     In the first communications phase, it may possibly be negotiated which one of the subscriber stations of the bus system receives an at least intermittent exclusive, collision-free access to the bus in the following second communications phase. 
     In accordance with an example embodiment of the present invention, the device may furthermore have a transmitter module for transmitting messages onto a bus of the bus system, and the transmitter module is developed to switch between a first operating mode and a second operating mode during the transmission of the different communications phases of a message. In this context it is possible that in the first operating mode, the transmitter module is developed to generate a first data state as a bus state with different bus levels for two bus conductors of the bus line and to generate a second data state as a bus state with the same bus level for the two bus conductors of the bus line, and the transmitter module in the second operating mode is developed to generate the first and the second data state as a bus state with different bus levels for the two bus conductors of the bus line. 
     In addition, the device may have a receiver module for generating the receive signal from the signal received from the bus, the receiver module being developed to use a receive threshold in the first communications phase whose voltage value differs from a voltage value of a receive threshold in the second communications phase. 
     The above-described device may be part of a subscriber station for a serial bus system, which furthermore has a communications control device for controlling a communication of the subscriber station with at least one other subscriber station of the bus system. The device is connected to the communications control device in such a way that the signaling of the evaluation module is output to the communications control device. 
     In accordance with an example embodiment of the present invention, there is the option that the device is developed to signal the evaluation of the evaluation module to the communications control device by the receive signal or by a signal via a separate line in order to indicate a transmission conflict on the bus, and the communications control device is developed to generate or abort the transmit signal on the basis of the signal and/or to signal the transmission conflict to other subscriber stations of the bus system. 
     The above-described subscriber station may be part of a bus system that furthermore includes a bus and at least two subscriber stations, which are connected to one another via the bus in such a way that they are able to serially communicate with one another. At least one of the two subscriber stations is an above-described subscriber station. 
     The above-mentioned objective may furthermore be achieved by a method for communication in a serial bus system in accordance with the present invention. In accordance with an example embodiment of the present invention, the method has the steps of counting, using a transmit signal analysis module, edges of a transmit signal that is to be transmitted on a bus of the bus system in order to exchange a message between subscriber stations of the bus system; counting, using a receive signal analysis module, edges of a receive signal that is generated from a signal transmitted on the bus because of the transmit signal, in which the bus states of the signal for the message in a first communications phase differ from bus states of the signal received in a second communications phase; and evaluating, using an evaluation module, the difference that results from a comparison of the edges counted by the transmit signal analysis module and the edges counted by the receive signal analysis module; signaling, using the evaluation module, in the event that the signal propagation time on the bus is greater than the bit time of the receive signal, whether the amount of the difference is less than or equal to a predefined value, or whether the amount of the difference is greater than the predefined value, the predefined value being greater than zero. 
     The method offers the same advantages as those mentioned above in connection with the device and/or the subscriber station. 
     Additional possible implementations of the present invention also include not explicitly mentioned combinations of features or embodiments described in the previous or following text with regard to the exemplary embodiments. One skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the present invention, in view of the disclosure herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the present invention will be described in greater detail with reference to the figures and based on exemplary embodiments. 
         FIG. 1  shows a simplified circuit diagram of a bus system according to a first exemplary embodiment of the present invention. 
         FIG. 2  shows a diagram to illustrate the structure of messages able to be transmitted by a transceiver for a subscriber station of the bus system according to the first exemplary embodiment of the present invention. 
         FIG. 3  shows a simplified schematic circuit diagram of a subscriber station of the bus system according to the first exemplary embodiment of the present invention. 
         FIG. 4  shows an example of a time characteristic of a transmit signal TxD, which a subscriber station of the bus system according to the first exemplary embodiment of the present invention transmits onto a bus of the bus system. 
         FIG. 5  shows a time characteristic of bus signals CAN-XL_H and CAN-XL_L, which come about on the bus in a normal operation as a result of transmit signal TxD of  FIG. 4 . 
         FIG. 6  shows a time characteristic of a differential voltage VDIFF, which results from the bus signals CAN-XL_H and CAN-XL_L of  FIG. 5 . 
         FIG. 7  shows a time characteristic of a receive signal Rx_In, which a subscriber station of the bus system receives from the bus and/or generates from the signals from  FIG. 5  and  FIG. 6 . 
         FIG. 8  shows an example of a time characteristic of a transmit signal TxD 1  in a data phase of a message that is transmitted by a first subscriber station of the bus system according to the first exemplary embodiment of the present invention. 
         FIG. 9  shows an example of a time characteristic of a transmit signal TxD 2  that is transmitted by another subscriber station for aborting the transmit signal TxD 1  of  FIG. 8 . 
         FIG. 10  shows a time characteristic of bus signals CAN-XL_H and CAN-XL_L that come about on the bus because of transmit signals TxD 1 , TxD 2  of  FIG. 8  and  FIG. 9 . 
         FIG. 11  shows a time characteristic of a differential voltage VDIFF, which results from bus signals CAN-XL_H and CAN-XL_L of  FIG. 10 . 
         FIG. 12  shows a time characteristic of a receive signal Rx_In, which a subscriber station of the bus system receives from the bus or generates from the signals of  FIG. 10  and  FIG. 11 . 
         FIG. 13  shows a simplified schematic block diagram of a subscriber station of the bus system according to a second exemplary embodiment of the present invention. 
     
    
    
     Unless otherwise indicated, identical or functionally equivalent elements in the figures have been provided with the same reference numerals. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     As an example,  FIG. 1  shows a bus system  1 , which in particular is basically configured for a CAN bus system, a CAN FD bus system, a CAN XL bus system and/or variations thereof as will be described in the following text. Bus system  1  may be used in a vehicle, in particular a motor vehicle, an airplane, etc. or in a hospital, etc. 
     In  FIG. 1 , bus system  1  has a multitude of subscriber stations  10 ,  20 ,  30 , which are connected to a bus  40  in each case via a first bus conductor  41  and a second bus conductor  42 . Bus conductors  41 ,  42  may also be referred to as CAN_H and CAN_L or CAN-XL_H and CAN-XL_L and are used for an electrical signal transmission after coupling the differential levels or generating recessive levels for a signal in the transmission state. Messages  45 ,  46  in the form of signals are serially transmittable via bus  40  between the individual subscriber stations  10 ,  20 ,  30 . If an error occurs during the communication on bus  40 , as illustrated by the jagged black block arrow in  FIG. 1 , then an error frame  47  (error flag) can be transmitted. Subscriber stations  10 ,  20 ,  30 , for example, are control units, sensors, display devices, etc. of a motor vehicle. 
     As illustrated in  FIG. 1 , subscriber station  10  has a communications control device  11 , a transceiver  12 , and an error detection device  15 . Subscriber station  20 , on the other hand, has a communications control device  21  and a transceiver  22 . Subscriber station  30  has a communications control device  31 , a transceiver  32  and an error detection device  35 . Transceivers  12 ,  22 ,  32  of subscriber stations  10 ,  20 ,  30  are directly connected to bus  40  in each case even if this is not illustrated in  FIG. 1 . 
     Communication control devices  11 ,  21 ,  31  are used for the control of a communication of respective subscriber station  10 ,  20 ,  30  via bus  40  with at least one other subscriber station of subscriber stations  10 ,  20 ,  30  connected to bus  40 . 
     Communications control device  11  prepares and reads first messages  45  which are modified CAN messages  45 , for instance. Modified CAN messages  45  are structured on the basis of a CAN XL format, which is described in greater detail with regard to  FIG. 2 . 
     Communications control device  21  may be developed like a conventional CAN controller according to ISO 11898-1:2015. Communications control device  21  prepares and reads second messages  46  such as classic CAN messages  46 . Classic CAN messages  46  are structured according to the classic basic format in which up to 8 data bytes may be included in message  46 . Alternatively, a classic CAN message  46  is set up as a CAN FD message which may include up to 64 data bytes, which are furthermore transmittable at a considerably faster data rate than in a classic CAN message  46 . In the latter case, communications control device  21  is developed like a conventional CAN FD controller. 
     Depending on the requirements, communications control device  31  may be developed to supply a CAN XL message  45  or a classic CAN message  46  for transceiver  32  or to receive such a message from transceiver  32 . Communications control device  31  thus prepares and reads a first message  45  or a second message  46 , which differ by their data transmission standard, in this case, CAN XL or CAN. Alternatively, classic CAN message  46  is set up like a CAN FD message. In the latter case, communications control device  31  is embodied like a conventional CAN FD-controller. 
     With the exception of the differences still to be described in greater detail in the following text, transceiver  12  may be developed as a CAN XL transceiver. Transceiver  22  may be developed like a conventional CAN transceiver or a CAN FD transceiver. Depending on the requirements, transceiver  32  can be developed to supply messages  45  for communications control device  31  according to the CAN XL format or messages  46  according to the current CAN basic format or to receive such therefrom. Transceivers  12 ,  32  may additionally or alternatively be developed like a conventional CAN FD transceiver. 
     With the aid of the two subscriber stations  10 ,  30 , messages  45  can be created and then transmitted using the CAN XL format and such messages  45  are also able to be received. 
       FIG. 2  shows a CAN XL frame  450  for message  45  as it is transmitted by transceiver  12  or transceiver  32 . CAN XL frame  450  is subdivided into different communications phases  451  to  453  for the CAN communication on bus  40 , i.e., an arbitration phase  451 , a data phase  452 , and an end-of-frame phase  453 . 
     In arbitration phase  451 , a negotiation takes place between subscriber stations  10 ,  20 ,  30  with the aid of an identifier in a bitwise manner as to which subscriber station  10 ,  20 ,  30  wants to transmit message  45 ,  46  at the highest priority and thus receives exclusive access to bus  40  of bus system  1  next time for the transmission in subsequent data phase  452 . 
     In data phase  452 , the useful data of CAN XL frame or message  45  are transmitted. The useful data may have up to 4096 bytes, for instance, or a higher value according to the value range of a data length code. 
     Included in end-of-frame phase  453 , e.g., in a check sum field, may be a check sum about the data of data phase  452  including the stuff bits, which the transmitter of message  45  inserts as an inverse bit after a predefined number of similar bits, in particular 10 similar bits. In addition, at least one acknowledgement bit may be included in an end field in end-of-frame phase  453 . A sequence of 11 similar bits may furthermore be present that indicates the end of CAN XL frame  450 . Using the at least one acknowledgement bit, it can be indicated whether or not a receiver has discovered an error in received CAN XL frame  450  or message  45 . 
     In arbitration phase  451  and end-of-frame phase  453 , a physical layer as in CAN and CAN FD is used. The physical layer corresponds to the bit transmission layer or layer  1  of the conventional OSI model (Open System Interconnection model). 
     An important point during phases  451 ,  453  is that the conventional CSMA/CR method is used, which allows for simultaneous access of subscriber stations  10 ,  20 ,  30  to bus  40  without destroying the higher-prioritized message  45 ,  46 . This makes it relatively easy to add further bus subscriber stations  10 ,  20 ,  30  to bus system  1 , which is very advantageous. 
     The CSMA/CR method means that what is known as recessive states must exist on bus  40 , which are able to be overwritten with dominant states by other subscriber stations  10 ,  20 ,  30  on bus  40 . In the recessive state, high-impedance conditions prevail at the individual subscriber station  10 ,  20 ,  30 , which in combination with the parasites of the bus circuitry result in longer time constants. This leads to a restriction of the maximum bit rate of the current CAN FD physical layer to presently approximately 2 megabits per second in an actual vehicle use. 
     A transmitter of message  45  starts a transmission of bits of data phase  452  on bus  40  only when subscriber station  10  as the transmitter has won the arbitration and subscriber station  10  as the transmitter thus has exclusive access to bus  40  of bus system  1 . 
     Quite generally, compared to CAN or CAN FD, the following deviating characteristics are able to be realized in the bus system with CAN XL:
     a) Adopting and possibly adapting proved and tested characteristics that are responsible for the robustness and application ease of CAN and CAN FD, in particular the frame structure with identifier and arbitration according to the CSMA/CR method,   b) Increasing the net data transmission rate to approximately 10 megabits per second,   c) Increasing the size of the useful data per frame to approximately 4 Kbytes.   

       FIG. 3  shows the basic structure of subscriber station  10  having communication control device  11 , transceiver  12  and error detection device  15 . Subscriber station  30  has a similar development to that shown in  FIG. 3 , with the exception that error detection device  35  is not integrated into transceiver  32  but is provided separately from communications control device  31  and transceiver  32 . For that reason, subscriber station  30  and error detection device  35  will not be described separately. The functions of device  15  described in the following text are provided identically in device  35 . 
     According to  FIG. 3 , in addition to communications control device  11 , transceiver  12  and device  15 , subscriber station  10  also has a microcontroller  13  to which communications control device  11  is allocated, and a system ASIC  16  (Application-Specific Integrated Circuit), which alternatively may be a system basic chip (SBC) on which multiple functions required for an electronics module of subscriber station  10  are combined. Apart from transceiver  12 , an energy supply device (not shown), which supplies electrical energy to transceiver  12 , is installed in system ASIC  16 . The energy supply device usually supplies a voltage CAN_supply of 5V. Depending on the requirements, however, a different voltage having a different value may be supplied by the energy supply device. Additionally or alternatively, the energy supply device may be developed as a current source. 
     Error detection device  15  has a transmit signal analysis module  151 , a receive signal analysis module  152 , and an evaluation unit  153 . Transmit signal analysis module  151  is particularly developed as at least one first counter. Receive signal analysis module  151  is particularly developed as at least one second counter. 
     Transceiver  12  furthermore has a transmitter module  121 , a receiver module  122 , a transmit signal driver  123  and a receive signal driver  124 . Even if the following text always refers to transceiver  12 , it is alternatively possible to provide receiver module  122  with its receive signal driver  124  in a separate device, externally to transmitter module  121  with its transmit signal driver  123 . Transmitter module  121  and receiver module  122  as well as transmit signal driver  123  and receive signal driver  124  may have the structure of a conventional transceiver  22 . Transmitter module  121  may particularly have at least one operational amplifier and/or one transistor. Receiver module  122  may especially have at least one operational amplifier and/or one transistor. 
     Transceiver  12  is connected to bus  40 , more precisely, to its first bus conductor  41  for CAN_H or CAN-XL_H and its second bus conductor  42  for CAN_L or CAN-XL_L. 
     First and second bus conductors  41 ,  42  in transceiver  12  are connected not only to transmitter module  121 , also referred to as a transmitter, but also to receiver module  122 , also referred to as a receiver. First and second bus conductors  41 ,  42  in transceiver  12  are also connected to device  15  even if the connection is not shown in  FIG. 3  for reasons of clarity. 
     While bus system  1  is in operation, transmitter module  121  converts a transmit signal TXD or TxD of communications control device  11  according to  FIG. 4  into corresponding signals CAN-XL_H and CAN-XL_L according to  FIG. 5  for bus conductors  41 ,  42  and transmits these signals CAN-XL_H and CAN-XL_L at the connections for CAN-XL_H and CAN-XL_L onto bus  40 , as illustrated in  FIG. 3 . The signals of  FIG. 5  cause a differential voltage VDIFF=CAN-XL_H−CAN-XL_L to form on bus  40 , which is illustrated in  FIG. 6 . 
     Receiver module  122  uses the CAN-XL_H and CAN-XL_L signals received from bus  40  according to  FIG. 5  or their differential voltage VDIFF according to  FIG. 6  to form a receive signal Rx_In as illustrated in  FIG. 7 , and outputs it to error detection device  15 , which forwards signal Rx_In in a normal operation as an RXD or RxD signal to communications control device  11 , as illustrated in  FIG. 3 . Receive signal Rx_In is forwarded in arbitration phase  451  as signal RxD. However, if subscriber station  10  is a transmitter in data phase  452 , then it is not forwarded as signal RxD in at least one embodiment variant, that is to say, when a possible conflict is signaled via the RxD line. In such a case, receive signal Rx_In then is known only internally in transceiver  12 , possibly only in receiver module  122  and device  15 . Protocol control unit  111  simply needs to know whether or not a conflict exists or whether its bits are transmitted without any problems via connection TXD. 
     With the exception of an idle or standby state, transceiver  12  with receiver module  122  always listens for a transmission of data or messages  45 ,  46  on bus  40  during a normal operation, and does so regardless of whether or not transceiver  12  is a transmitter of message  45 . 
     Even if this is not explicitly indicated in  FIGS. 4 to 7 , the bit rate in phases  451 ,  453 , i.e., in an arbitration and end-of-frame, has a value of maximally 1 Mbit/s. On the other hand, the bit rate in data phase  452  may have the same value as illustrated in  FIG. 4  to  FIG. 7  or a higher value, especially 8 Mbit/s or 10 Mbit/s or even higher. In such a case, a bit time t_bt 1  in phases  451 ,  453  is considerably longer than a bit time t_bt 2  in data phase  452 . 
     According to the example of  FIG. 5 , CAN-XL_H and CAN-XL_L signals in the above-mentioned communications phases  451 ,  453  have the dominant and recessive bus levels  401 ,  402 , as from CAN. In contrast, the CAN-XL_H and CAN-XL_L signals in data phase  452  differ from conventional signals CAN_H and CAN_L, as will be described in greater detail in the following text. 
     As may be gathered from the left part of  FIG. 5 , transmitter module  121  drives dominant states  402  of differential signals CAN-XL_H and CAN-XL_L differently only in the above-mentioned communications phases  451 ,  453 . In contrast, the bus levels on bus line  3  for recessive states  401  in the above-mentioned communications phases  451 ,  453  are equal to voltage Vcc or the CAN_supply of 2.5V, for instance. Thus, a value of 0V results for a voltage VDIFF=CAN-XL_H−CAN-XL_L for recessive states  401  (logical ‘1’ or H of transmit signal TxD), and a value of approximately 2.0V for dominant states  402  (logical ‘0’ or L of transmit signal TxD). 
     If transceiver  12 , in particular its device  15 , detects the end of arbitration phase  451 , then transmitter module  121  is switched for data phase  452  from the state shown in the left part of  FIG. 4  to a state shown in the right part of  FIG. 4 . Transmitter module  121  thus is switched from a first operating mode (arbitration phase  451 —classic CAN) to a second operating mode (data phase  452  as a transmitter of message  45 ) or to a third operating mode (data phase  452  as a receiver but not a transmitter of message  45 ). The second and the third operating modes differ in the following way. 
     In the third operating mode, the receiving subscriber station does not switch its bus driver or its transmitter module  121 , but outputs only “recessive”, i.e., bus state  401 , or does not drive CAN bus  40 . In addition, the receiving subscriber station switches its sampling threshold for VDIFF to threshold T_d. There is no need for a receiving subscriber station to detect a conflict because it does not transmit anything. Instead, a receiving subscriber station naturally requires the RxD input signal. 
     In the second operating mode, on the other hand, the transmitting subscriber station always actively drives one of two levels U_D 0 , U_D 1 . In addition, the transmitting subscriber station may ignore current input signal Rx_In or RxD as long as the bit errors are reported to communications control device  11 . In this particular exemplary embodiment, only the second operating mode is examined (data phase  452  as a transmitter of message  45 ). 
     In the possibly faster data phase  452 , bus states U_D 0 , U_D 1  according to data states Data_ 0  or L and Data_ 1  or H of transmit signal TXD of  FIG. 4  come about for CAN-XL_H, CAN-XL_L signals because of transmit signal TxD in the right part of  FIG. 4  according to  FIG. 5 . 
     The sequence of data states Data_ 0  or L and Data_ 1  or H in transmit signal TxD of  FIG. 4  and thus bus states U_D 0 , U_D 1  resulting therefrom for CAN-XL_H, CAN-XL_L signals in  FIG. 5  and the resulting characteristic of voltage VDIFF of  FIG. 6  serve only to illustrate the function of transceiver  12 . The sequence of data states Data_ 0  or L and Data_ 1  or H in transmit signal TxD and thus the bus states U_D 0 , U_D 1  is selectable according to the requirements. 
     In the above-described states, bus levels ranging from approximately −0.6V to approximately −2V exist on the bus line of bus  40  at the state Data_ 0 , and bus levels ranging from approximately 0.6V to approximately 2V exist at the state Data_ 1 . At the states Data_ 0  and Data_ 1 , differential voltage has VDIFF=CAN-XL_H−CAN-XL_L, i.e., in particular a maximum amplitude of approximately 1.4V, even if  FIG. 6  shows an amplitude for VDIFF as 2V in a special example. 
     In other words, in a first operating mode according to  FIG. 4 , transmitter module  121  generates a first data state such as Data_ 0  or L as bus state  402  with different bus levels for two bus conductors  41 ,  42  of the bus line, and a second data state such as Data_ 1  or H as bus state  401  with the same bus level for the two bus conductors  41 ,  42  of the bus line of bus  40 . 
     In addition, for the time characteristics of signals CAN-XL_H, CAN-XL_L in a second operating mode, which includes data phase  452 , transmitter module  121  forms first and second data state Data_ 0 , Data_ 1  as bus state U_D 0 , U_D 1  with different bus levels in each case for the two bus conductors  41 ,  42  of the bus line of bus  40 . This is shown in  FIG. 5  and  FIG. 6 . 
     As illustrated in  FIG. 6 , receiver module  122  uses the first receive threshold T a, from CAN/CAN-FD, in communications phases  451 ,  453 , especially with the typical level of 0.7V according to IS011898-2:2016, in order to be able to detect bus states  401 ,  402  in a reliable manner in the first operating mode. In contrast, receiver module  122  uses a receive threshold T_d which lies at approximately 0V in data phase  452 . 
       FIG. 8  through  FIG. 12  show a signal characteristic of signals TxD 1 , TxD 2  and of signals CAN-XL_H, CAN-XL_L for data phase  452 , their differential voltage VDIFF=CAN-XL_H−CAN-XL_L and the resulting receive signal RxD. In the case illustrated in  FIG. 8  to  FIG. 12 , for example, transmitter module  121  transmits transmit signal TxD 1  from  FIG. 8  for a frame  450 ; and subscriber station  30 , for example, which is actually only the receiver of frame  450  in data phase  452 , wants to achieve an abort of frame  450  and therefore transmits transmit signal TxD 2  from  FIG. 9 . 
     There are various reasons why an abort of frame  450  is to take place such as:
         subscriber station  30  as an RX subscriber station has to transmit a message  45 ,  46  with a higher priority, and/or   subscriber station  30  as an RX subscriber station has detected an error in the header check sum (CRC=Cyclic Redundancy Check) of CAN XL message  45  and would like to signal this fact, and/or   subscriber station  20 , which is a CAN FD subscriber station, has possibly not recognized the switchover to the format of frame  450  due to a bit error and transmits an error frame  47  during data phase  452  of frame  450 .       

     For example, if subscriber station  30  wants to obtain an abort of frame  450  which transmitter module  121  transmits to subscriber station  10  by signal TxD 1  from  FIG. 8 , then subscriber station  30  transmits transmit signal TxD 2  according to  FIG. 9  to bus  40 . As a result, the signal characteristics for CAN-XL_H and CAN-XL_L and their differential voltage VDIFF come about. In phase  455  of transmitting error frame  47 , which starts with the falling edge of transmit signal TxD 2 , voltage states thus result on bus  40  that deviate from the voltage states on bus  40  during a normal operation of data phase  452  and which have been described above with reference to  FIG. 4  to  FIG. 7 . 
     Quite generally, it is the case that the transmitting subscriber station sending transmit signal TxD 1  switches to an operation in data phase  452  in which both logic levels of transmit signals TxD, TxD 1 , TxD 2  are driven onto bus  40  at different differential voltages. In contrast, receive threshold Td is switched on for all receiving subscriber stations such as subscriber station  30  in the mentioned example. However, the bus driver of receiving subscriber station  30  remains in the receiving state (CAN-recessive-state) until receiving subscriber station  30  possibly sends error frame  47 , as illustrated in  FIG. 9  and mentioned above for transmit signal TxD 2 . Error frame  47  according to the right part of  FIG. 9  may then be sent as “dominant” or as differential voltage VDIFF for logic level ‘0’. Because both alternatives are possible, the two states in  FIG. 9  for transmit signal TxD 2  are denoted by P for passive and A for active. For an interoperability with CAN/CAN-FD, error frame  47  is selectable by lining up 6 or more bits (depending on the bit stuffing method) with a positive VDIFF. 
     In  FIG. 9  error frame  47  begins with the falling edge at TxD 2  at an instant t 1 . As a result of what is denoted as phase  455  in  FIG. 9 , the transient characteristic of differential voltage VDIFF in  FIG. 11  changes significantly. As schematically illustrated in  FIG. 12  by elliptical region  50 , this may lead to an unrecognized recessive pulse at receive signal Rx_In. 
     Going beyond the illustration in  FIG. 11 , differential voltage VDIFF in a real case is also superposed by high-frequency oscillations, which are defined by the bus topology, phase position and impedance of subscriber station  10 ,  20 ,  30  transmitting error frame  47 . 
     Since certain errors on bus  40  are unable to be detected even with additional receive thresholds in data phase  452 , error detection device  15  is provided. 
     With the aid of transmit signal analysis module  151 , error detection device  15  detects signal TxD, which, coming from communications control device  11 , more precisely, its protocol control unit  111 , is provided by TxD driver  123 . Thus, the mentioned signal TxD may be either signal TxD from  FIG. 4  or signal TxD 1  from  FIG. 8  or signal TxD 2  from  FIG. 9 . In addition, using its receive signal analysis module  152 , error detection device  15  detects the Rx_In output signal of receiver module  122 , as shown in  FIG. 8  or  FIG. 12 , for example. The RxD output signal is then made available via RxD driver  124  for communications control device  11 , more precisely, its protocol control unit  111 . 
     In the process, transmit signal analysis module  151  counts the number of edges of signal TxD, in particular each falling edge. Each edge on transmit signal TxD is implemented on bus  40  and received again and detected by receiver module  122  of respective subscriber station  10 ,  20 ,  30 . Receive signal analysis module  152  counts the number of edges of signal RxD, in particular each falling edge. 
     The counting of the edges by modules  151 ,  152  may be clocked using signals Rx_In and TxD. For instance, modules  151 ,  152  may increment their edge count value with each falling edge. When using signals Rx_In and TxD as the clock, modules  151 ,  152  and/or device  15  may have at least one filter module which filters out overshoots at the edges through suitable measures. The at least one filter module may particularly be or have a Schmitt trigger and/or a low-pass filter. 
     Evaluation module  153  forms the difference of the two count values of the edges of module  151 ,  152 . In this way, the two counter readings or count values of modules  151 ,  152  are compared to each other. The check instant or the evaluation instant by evaluation module  153  is specified to the instant after the RxD increment. If the signal propagation time is less than the bit length, the count values of modules  151 ,  152  at the check instant or the evaluation instant by evaluation module  153  are identical. If the signal propagation time is greater than the bit length, the signal propagation time is compensated by tolerating a small difference between the count values of modules  151 ,  152 . The tolerated difference, which may also be referred to as a tolerance value, is configurable in evaluation module  153  as a function of the signal propagation time and bit length. For instance, at a signal propagation time of max. 250 ns from transmit signal TXD to the receiving of receive signal RX_In at device  12  and a bit time t_bt 2  of 100 ns, the tolerated difference≤3. The difference may be specified as any natural number N that is equal to or greater than 1. 
     In other words, in a fault-free normal case, the difference of the two count values of the edges of module  151 ,  152  is zero. 
     If the difference is not equal to zero, then this points to an interruption or an error. Such an interruption or error may particularly occur on account of an error frame  47  of another subscriber station  10 ,  20 ,  30 , as described above. This is because transmitter  121  then no longer has exclusive, collision-free access to bus  40  in data phase  452 . 
     Device  15  thus detects a conflict on bus  40  if the difference between the two count values of modules  151 ,  152  is greater than the allowed tolerance value at the evaluation instant. 
     The conflict is then reported to communications control device  11 , more precisely, its protocol control unit  111 . In this particular exemplary embodiment, the RxD connection is used for this purpose during data phase  452 . The transmitter of CAN XL frame  450  then expects a constant H level (high level) at the RxD connection in a conflict-free operation, for example. However, if device  15  detects a conflict, an L level (low level), for instance, is output at the RxD connection in order to report the conflict to communications control device  11 , more precisely, to its protocol control unit  111 . It is of course possible to signal the conflict by a different signal pattern via the RxD connection. 
     As a result, device  15  does not need a protocol control unit of its own but the already present protocol control unit  111  of communications control device  11  suffices. This is a great advantage over an implementation in which evaluation unit  153  directly compares the two signals to each other in order to detect that an error frame  47  is sent by another node in a deviation between the two signals TxD, Rx_In. In such a comparison of the two signals TxD, Rx_In, the signal propagation time, in particular on bus  40 , would have to be taken into account, i.e., compensated, because at a bit rate of 10 Mbit/s, for example, the bit time amounts to 100 ns, which is below the signal propagation time of up to 250 ns. This would require an additional protocol control unit  111  in device  15 . 
     In data phase  452 , communications control device  11  reacts to the signaled transmission conflict by aborting data phase  452  and possibly additionally by transmitting a bit pattern that signals the end of data phase  452  to the other subscriber stations  20 ,  30 . 
     A particular advantage of the above-described variants of the evaluation is that the embodiment of receiver  122  or transceiver  12  is able to be used both for homogeneous CAN XL bus systems, in which only CAN XL messages  45  and no CAN FD messages  46  are transmitted, and for mixed bus systems, in which either CAN XL messages  45  or CAN FD messages  46  are transmitted. Transceiver  12  is therefore universally usable. 
       FIG. 13  illustrates an embodiment of an error detection device  150  for transceiver  12  according to a second exemplary embodiment. With the exceptions described in the following text, error detection device  150  is developed like an error detection device  15  according to the preceding exemplary embodiment. 
     According to  FIG. 13 , error detection device  150  in module  151  has a first and a second counter  1511 ,  1512 . In addition, module  152  has a first and a second counter  1521 ,  1522 . 
     With the aid of first counter  1511 , module  151  detects falling edges of transmit signal TxD. With the aid of second counter  1512 , module  151  detects rising edges of transmit signal TxD. Using first counter  1521 , module  152  detects falling edges of receive signal Rx_In. Using second counter  1522 , module  152  detects rising edges of receive signal Rx_In. 
     As a result, evaluation module  153  is is able to compare the count values of counters  1511 ,  1521 , that is to say, the number of falling edges in signals TxD, Rx_In. Additionally or alternatively, evaluation module  153  is able to compare the count values of counters  1512 ,  1522 , that is to say, the number of rising edges in signals TxD, Rx_In. Additionally or alternatively, evaluation module  153  is able to compare the count values of counters  1512 ,  1522 , or in other words, the number of falling edges in signal TxD and the number of falling edges in signal Rx_In. In addition or as an alternative, evaluation module  153  is able to compare the count values of counters  1512 ,  1522 , i.e., the number of falling edges and the number of rising edges in signal TxD. Additionally or alternatively, evaluation module  153  is able to compare the count values of counters  1521 ,  1522 , i.e., the number of falling edges and the number of rising edges in signal Rx_In. A tolerance value is able to be configured for each comparison. 
     This allows for an even further plausibilization of the existence of a transmission conflict on bus  40 . It may be distinguished between the conflict case of a transmission of an error frame  47  (error flag) and the conflict case of the transmission because of the undetected lost arbitration. 
     As a result, it can be signaled in receive signal RXD and/or signal S 1  to communications control device  11  which transmission conflict has occurred. If receive signal Rx_In is also to be forwarded in a conflict case in data phase  452  as signal RxD, then the possible conflict is signaled only by signal S 1  but not signaled via the RxD line. In other words, if Rx_In is always to be forwarded to communications control device  11 , then an additional line is required to signal the conflict. 
     Communications control device  11  is therefore able to carry out not only the aborting of data phase  452  but, if warranted, can additionally signal to the other subscriber stations  20 ,  30  the end of data phase  452  by the transmission of a bit pattern, and optionally provide information about the type of transmission conflict. 
     Alternatively or additionally, evaluation module  123  or some other module of transceiver  12  is able to generate a separate signal S 1 , which is transmitted via a separate signal line to communications control device  11  and which in particular has at least one switching pulse or a predefined bit pattern for signaling the conflict. Because the transmission conflict is signaled to communications control device  11  in data phase  452 , the conventional bit error check in the classic CAN by comparing transmit signal TXD to receive signal RXD is able to be replaced by a check of the conflict-signaling signal. The conflict-signaling signal in particular has a predefined bit pattern that signals the transmission conflict. In particular, the conflict-signaling signal may transmit a ‘1’ as an “OK signal” and an ‘0’ as a “conflict report”. 
     All above-described embodiments of devices  15 ,  35  of subscriber stations  10 ,  20 ,  30  of bus system  1  and the method carried out therein may be used individually or in all possible combinations. In particular, all features of the above-described exemplary embodiments and/or their modifications are combinable as desired. In addition or as an alternative, the following modifications are possible, in particular. 
     Device  15  may be switched on independently of the different communications phases  451 ,  452 ,  453  or may be switched on only in data phase  452 . In the latter case, however, device  15  must receive a corresponding switching pulse for the switch-on or switch-off. For example, this is realizable via the additional line by way of which switching signal S 1  is transmitted, as described above with reference to the first exemplary embodiment. 
     Receive threshold T_d shown in the figures is based on the assumption that bus states U_D 0 , U_D 1  in bus system  1  are driven inversely to one another at VDIFF levels that are identical in terms of their amounts. However, it is alternatively possible to adapt receive threshold T_d accordingly if bus states U_D 0  and U_D 1  are driven at two different positive VDIFF levels, for example. 
     Even if the present invention has been described above using the CAN bus system as the example, the present invention may be used in any communications network and/or communications method in which two different communications phases are used in which the bus states that are generated for the different communications phases differ. In particular, the present invention may be used in developments of other serial communications networks such as Ethernet, and/or 100 Base-T1 Ethernet, field bus systems and others. 
     Bus system  1  according to the exemplary embodiments may particularly be a communications network in which data are serially transmittable using two different bit rates. It is advantageous but not a mandatory requirement that an exclusive, collision-free access of a subscriber station  10 ,  20 ,  30  to a shared channel is ensured in bus system  1  at least for certain time periods. 
     The number and arrangement of subscriber stations  10 ,  20 ,  30  in bus system  1  of the exemplary embodiments can be selected as desired. In particular, subscriber station  20  may be omitted in bus system  1 . It is possible that one or more of subscriber station(s)  10  or  30  is/are available in bus system  1 . It is possible that all subscriber stations in bus system  1  have an identical development, that is to say, only subscriber station  10  or only subscriber station  30  is provided. 
     All above-described variants for the detection of the transmission conflict may be subject to time filtering in order to improve the robustness with regard to electromagnetic compatibility (EMC) and with regard to electrostatic charges (ESC), pulses and other interference. 
     It is furthermore possible to shorten the bit period t_bt 2  in data phase  452  in comparison with bit period t_bt 1  in arbitration phase  451  and end-of-frame phase  453 . In this case, a transmission at a greater bit rate takes place in data phase  452  than in arbitration phase  451  and end-of-frame phase  453 . This allows for an even further increase in the transmission speed in bus system  1 .