DE102018214960A1 - Subscriber station for a serial bus system and method for sending a message in a serial bus system - Google Patents

Abstract

A subscriber station (20; 30) for a bus system (1) and a method for sending a message with different bit rates are provided in a bus system (1). The subscriber station (20; 30) comprises a transceiver (22; 32) for the serial transmission of a message (5) on a bus line (3) to at least one other subscriber station (10; 20; 30) of the bus system (1) or for serial reception of a message (5) from the bus line (3), the transceiver (22; 32) being designed, for serial transmission and / or serial reception of the message (5) between a first operating mode and a second To switch the operating mode, the transmitting / receiving device (22; 32) being designed in the first operating mode, a first and a second data state each as a bus state (DF1, DF3; DF1, DF2) with different bus levels for two bus wires (41, 42) to generate the bus line (3), and wherein the transmitting / receiving device (22; 32) is designed in the second operating mode, in addition to the first and second data state, a third data state as bus state (DF1, DF2, DF3) with a bus level forto generate the two bus wires (41, 42) of the bus line (3), which differs from the bus levels for the first and second data states (DF1, DF2).

Description

Technical field

The present invention relates to a subscriber station for a serial bus system and a method for sending a message in a serial bus system which operates with a high data rate and a high level of error tolerance.

State of the art

A bus system is frequently used for communication between sensors and control devices, for example in vehicles, in which data is transmitted as messages in the ISO11898-1: 2015 standard as a CAN protocol specification with CAN FD. The messages are transmitted between the bus participants in the bus system, such as sensors, control units, transmitters, etc.

With an increasing number of functions of a technical system or a vehicle, the data traffic in the bus system also increases. In addition, it is often required that the data can be transferred from the sender to the receiver faster than before. The consequence of this is that the required bandwidth of the bus system will continue to increase.

In order to be able to transmit data with a higher bit rate than with CAN, an option for switching to a higher bit rate within a message was created in the CAN FD message format. In such techniques, the maximum possible data rate is increased by using a higher clock rate in the area of the data fields beyond a value of 1 Mbit / s. Such messages are also referred to below as CAN FD frames or CAN FD messages. With CAN FD, the user data length is extended from 8 to up to 64 bytes and the data transfer rates are significantly higher than with CAN.

Even if a CAN or CAN FD-based communication network offers many advantages in terms of its robustness, for example, it has a significantly lower speed compared to data transmission with 100 Base-T1 Ethernet, for example. In addition, the user data length of up to 64 bytes previously achieved with CAN FD is too short for some applications.

Disclosure of the invention

It is therefore an object of the present invention to provide a subscriber station for a serial bus system and a method for sending a message in a serial bus system, which solve the aforementioned problems. In particular, a subscriber station for a serial bus system and a method for sending a message in a serial bus system are to be provided, in which a high data rate and an increase in the amount of user data per frame can be realized with great robustness for errors.

The aforementioned object is achieved by a subscriber station for a serial bus system according to claim 1. The subscriber station has a transceiver for serial transmission of a message on a bus line to at least one other subscriber station of the bus system and / or for the serial reception of a message from the bus line, the transceiver being designed for serial transmission and / or for to switch the serial reception of the message between a first operating mode and a second operating mode, the transceiver in the first operating mode being designed to generate a first and a second data state in each case as a bus state with different bus levels for two bus wires of the bus line, and wherein the Transceiver in the second operating mode is configured to generate a third data state as a bus state with a bus level for the two bus wires of the bus line in addition to the first and second data state, which is different from the bus levels for the first and second data state.

With the subscriber station, it is possible in particular to maintain arbitration known from CAN in a first communication phase and yet to significantly increase the transmission rate again compared to CAN or CAN FD. This can be achieved in that by expanding the bus states or symbols from two to three by means of coding and decoding, more data is transmitted per time at a given transmission frequency. This leads to an increase in the baud rate. As a result, the bit rate and thus the transmission speed from the transmitter to the receiver can be increased significantly. However, due to the configuration of the three different bus states, great robustness against errors is guaranteed at the same time.

This helps to realize a net data rate of at least 10 Mbps. In addition, the size of the user data can be increased significantly, in particular up to 4096 bytes per frame or more or less if required.

The method carried out by the transmitting / receiving device can also be used if at least one CAN subscriber station and / or at least one CAN FD subscriber station is also present in the bus system and sends messages according to the CAN protocol and / or CAN FD protocol .

Advantageous further developments of the subscriber station are specified in the dependent claims.

According to one embodiment, the bus states for the first and second data states are symmetrical to one another.

According to a special embodiment, the transmitting / receiving device is designed to generate the bus state for the second data state by driving the bus levels for the two bus wires weaker than the bus state for the first data state.

The transmitting / receiving device is optionally designed to generate the bus states in such a way that the bus state for the first data state can overwrite both the bus state for the second data state and the bus state for the third data state.

According to a special embodiment, the transmitting / receiving device is configured to switch to the first operating mode if data of a first phase are to be sent from the message which are to be sent at a first bit rate, and the transmitting / receiving device is configured to switch to the second mode of operation if the message is to send data of a second phase which is to be sent at a second bit rate which is faster than the first bit rate. Here, the transmitting / receiving device may be designed to switch to the first operating mode or the second operating mode according to a predetermined coding if the data of the second phase are to be sent from the message.

It is conceivable that the transmitting / receiving device is designed to only switch to the second operating mode for transmitting data if exclusive, collision-free access to the bus line of the bus system is guaranteed for the subscriber station.

The transmitting / receiving device may be designed to send the data for the first and second data states to the bus line in the first operating mode with the same bus level as in the second operating mode.

In particular, the message can have a data field with a variable length, the variable length being between 1 byte and 4096 bytes.

The subscriber station described above can be part of a bus system which also comprises a bus line and at least two subscriber stations which are connected to one another via the bus line in such a way that they can communicate with one another in series. Here, at least one of the at least two subscriber stations is a previously described subscriber station.

The aforementioned object is also achieved by a method for sending a message in a serial bus system according to claim 11. The method has the step: serial transmission, with a transmitting / receiving device of a subscriber station of the bus system, a message on a bus line of the bus system, wherein the transmitting / receiving device can additionally be designed for the serial reception of a message from the bus line, the transmission - / receiving device for serial transmission switches between a first operating mode and a second operating mode, the transmitting / receiving device in the first operating mode generating a first and second data status as a bus status with different bus levels for two bus cores of the bus line, and wherein the transmitting / In the second operating mode, the receiving device generates, in addition to the first and second data states, a third data state as a bus state with a bus level for the two bus wires of the bus line which differs from the bus levels for the first and second data states.

The method offers the same advantages as previously mentioned with regard to the subscriber station.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with reference to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Figure list

• 1 ein vereinfachtes Blockschaltbild eines Bussystems gemäß einem ersten Ausführungsbeispiel;
• 2 ein Schaubild zur Veranschaulichung des Aufbaus von Nachrichten, die von Teilnehmerstationen des Bussystems gemäß dem ersten Ausführungsbeispiel gesendet werden können;
• 3 einen zeitlichen Verlauf von Bussignalen CAN_H und CAN_L bei der Sende-/Empfangseinrichtung gemäß dem ersten Ausführungsbeispiel; und
• 4 einen zeitlichen Verlauf einer Differenzspannung VDIFF der Bussignale CAN_H und CAN_L bei der Sende-/Empfangseinrichtung gemäß dem ersten Ausführungsbeispiel.

The invention is described in more detail below with reference to the accompanying drawing and using exemplary embodiments. Show it:

• 1 a simplified block diagram of a bus system according to a first embodiment;
• 2 a diagram illustrating the structure of messages that can be sent from subscriber stations of the bus system according to the first embodiment;
• 3 a time course of bus signals CAN_H and CAN_L in the transceiver according to the first embodiment; and
• 4 a time course of a differential voltage VDIFF of the bus signals CAN_H and CAN_L in the transceiver according to the first embodiment.

In the figures, identical or functionally identical elements are provided with the same reference numerals, unless stated otherwise.

Description of the embodiments

1 shows a bus system as an example 1 , which is configured in particular fundamentally for a CAN bus system, a CAN FD bus system, a CAN FE bus system, and / or modifications thereof, as described below. The bus system 1 can be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in a hospital, etc.

In 1 has the bus system 1 one, especially two twisted bus wires 41 . 42 having bus line 3 to which a variety of subscriber stations 10 . 20th . 30th are connected. About the in 1 very schematic, shown in partial sectional view, bus line 3 are news 4 . 5 in the form of signals between the individual subscriber stations 10 . 20th . 30th serially transferable. The subscriber stations 10 . 20th . 30th are, for example, control devices, sensors, display devices, etc. of a motor vehicle.

As in 1 has shown the subscriber station 10 a communication control device 11 and a transceiver 12 , The subscriber station 20th on the other hand has a communication control device 21 and a transceiver 22 , The subscriber station 30th has a communication control device 31 and a transceiver 32 , The sending / receiving devices 12 . 22 . 32 of the subscriber stations 10 . 20th . 30th are each directly to the bus line 3 , or their bus cores 41 . 42 , connected, even if this is in 1 is not illustrated.

The communication control devices 11 . 21 . 31 each serve to control communication of the respective subscriber station 10 . 20th . 30th over the bus line 3 with another subscriber station of the subscriber stations 10 . 20th . 30th that to the bus line 3 are connected.

The communication control device 11 can be designed like a conventional CAN controller. The communication control device 11 creates and reads first messages 4 , for example Classic CAN messages 4 , The Classic CAN messages 4 are structured according to the classic basic format, in which in the message 4 a number of up to 8 data bytes can be included. Alternatively, there is the Classic CAN message 4 constructed as a CAN FD message, in which a number of up to 64 data bytes can be included, which in addition with a significantly faster data rate than with the Classic CAN message 4 be transmitted. In the latter case, the communication control device 11 designed like a conventional CAN FD controller.

The communication control device 21 creates and reads second messages 5 which, for example, modified CAN messages 5 are. Here are the modified CAN messages 5 built on a CAN FE format that is related to 2 is described in more detail.

The communication control device 31 can be executed to create a Classic CAN message as needed 4 or a CAN FE message 5 for the transceiver 32 provide or receive from this. The communication control device 31 creates and reads a first message 4 or second message 5 , being the first and second message 4 . 5 distinguish by their data transmission standard, namely in this case CAN or CAN FE. Alternatively, there is the Classic CAN message 4 constructed as a CAN FD message. In the latter case, the communication control device 11 designed like a conventional CAN FD controller.

The transceiver 12 can be designed like a conventional CAN transceiver or CAN FD transceiver. The transceiver 22 can be designed as a CAN FE transceiver except for the differences described in more detail below. The transceiver 32 can be run to messages as needed 4 according to the current CAN base format or messages 5 according to the CAN FE format for the communication control device 31 provide or receive from this. The sending / receiving devices 22 . 32 can be implemented additionally or alternatively as a conventional CAN FD transceiver.

Each of the transceiver 12 . 22 . 32 is preferably designed to differentiate the bus states with respect to 0 and 2V differential voltage VDIFF. This also allows a receiving part of the transmitting / receiving device 12 . 22 . 32 recognize all states of the signals below in relation to 3 and 4 are described. Alternatively, the receiving part of the transmitting / receiving device 12 . 22 . 32 perform an appropriate switchover to the news 5 to be able to receive correctly.

With the two subscriber stations 20th . 30th can an education and then transfer of news 5 with the CAN FE format and the receipt of such messages 5 will be realized.

2 shows for the message 5 a CAN FE frame 45 as it is from the transceiver 22 or the transmitting / receiving device 32 is sent. The CAN FE frame 45 is for CAN communication on the bus line 3 divided into different fields, namely a start field 451 , an arbitration field 452 , a control panel 453 , a data field 454 , a checksum field 455 and an end field 456 ,

The starting field 451 has, for example, a bit that is also called SOF bit and indicates the start of the frame or start of frame. In the arbitration field 452 an identifier with, for example, 32 bits is included to identify the sender of the message. The arbitration field 452 can additionally contain protocol format information consisting of one or more bits, which is suitable for distinguishing CAN FE frames from CAN frames or CAN FD frames.

In the control panel 453 For example, a 13-bit data length code (data length code) is contained, which can then assume values from 1 to 4096 with the step size of 1, for example, or can also assume values from 0 to 4095. The data length code can also comprise fewer or more bits and the value range and the step-by-step can assume different values. The control panel 453 can additionally contain protocol format information consisting of one or more bits, which is suitable for distinguishing CAN FE frames from CAN frames or CAN FD frames.

In the data field 454 are the user data of the CAN FE frame or the message 5 contain. Depending on the value range of the data length code, the user data can have, for example, up to 4096 bytes. In the checksum field 455 is a checksum of the data in the data field 454 including the stuff bits contained by the sender of the message 5 after every 10 identical bits are inserted as an inverse bit. In the end field 456 it contains at least one acknowledge bit and also a sequence of 11 identical bits that represent the end of the CAN FE frame 45 Show. The at least one acknowledge bit can be used to indicate whether a receiver is in the received CAN FE frame 45 or the message 5 discovered an error or not.

In the phases for sending the arbitration field 452 and the end field 456 a physical layer like for CAN and CAN-FD is used. An important point during these phases is that the known CSMA / CR method is used, which simultaneous access by the subscriber stations 10 . 20th . 30th on the bus line 3 allowed without the higher priority message 4 . 5 gets destroyed. This allows the bus system 1 relatively easy further bus subscriber stations 10 . 20th . 30th be added, which is very beneficial.

The consequence of the CSMA / CR method is that there are so-called recessive states on the bus line 3 must be given by other subscriber stations 10 . 20th . 30th with dominant states on the bus line 3 can be overwritten. In a recessive state, the individual subscriber station prevails 10 . 20th . 30th high-impedance conditions, which, in combination with the parasites of the bus circuit, results in longer time constants. This leads to a limitation of the maximum bit rate of today's CAN FD physical layer to currently around 2 megabits per second in real vehicle use.

The control panel 453 and the data field 454 are from a sender of the message 5 first on the bus line 3 sent when the subscriber station 20th when the sender won the arbitration and the subscriber station 20th as sender to send the fields 453 to 456 exclusive access to the bus line 3 of the bus system 1 Has. Arbitration is carried out with the help of the identifier in the arbitration field 452 bit by bit between the subscriber stations 10 . 20th . 30th negotiated which subscriber station 10 . 20th . 30th the message 4 . 5 want to send with the highest priority and therefore for the next time to send the fields 453 to 455 exclusive access to the bus line 3 of the bus system 1 gets.

The arbitration at the beginning of a frame 45 or the message 4 . 5 and the acknowledgment in the end field 456 at the end of the frame 45 or the message 4 . 5 is only possible if the bit time is significantly more than twice as long as the signal transit time between any two subscriber stations 10 . 20th . 30th of the bus system 1 , Therefore, the bit rate in the arbitration phase when the fields are transmitted 451 . 452 . 456 chosen slower than in the other fields of the frame 45 ,

3 shows voltage curves of bus signals 412 . 422 according to a second embodiment. To simplify matters, only the part of the bus signals is included 412 . 422 shown, which is for the transfer of the fields 453 . 454 . 455 on the bus line 3 to adjust. With a CAN or CAN FD bus system, the bus signals 412 . 422 referred to as CAN-H and CAN_L and are each separately in the bus wires 41 . 42 fed. 4 shows the resulting differential voltage VDIFF = CAN_H - CAN_L.

The bus signals 412 . 422 that are in the arbitration phase when transferring the fields 451 . 452 . 456 can be set from the representation of 3 and or 4 derive as explained below.

For the realization of the bus signals 412 . 422 of 3 will be for the entire frame 45 of 2 a physical layer that uses the said arbitration phase for the fields 451 . 452 and 456 as well as a long and faster data phase for the fields 453 . 454 . 455 allowed. Here the transmitting / receiving devices work 22 . 32 to generate the bus signals 412 . 422 for a message 5 partially symmetrical in all communication phases.

In 3 are the resulting bus signals 412 . 422 in all three possible bus states DF1 . DF2 . DF3 in such a transceiver 22 . 32 shown. The amplitude U_D1 the differential voltage of the bus state DF1 and the amplitude U_D2 the differential voltage of the bus state DF2 is equal to. In contrast, the amplitude of the differential voltage U_D3 the bus state DF3 the value 0 ,

With the three different bus states DF1 . DF2 . DF3 after arbitration is completed in the data phase, i.e. in the fields 453 to 455 , communicates. The bus state DF1 results in a positive differential voltage VDIFF = U_D2 (V_Plus - V_Minus). The bus state DF2 results in a negative differential voltage Vdiff = -U_D2. The bus state DF3 results in a differential voltage VDIFF = U_D3 = 0. With the two different two bus states DF1 ("Positive dominant"), DF3 ("Negative dominant") is in the arbitration phase, ie in the fields 451 . 452 . 456 , communicates. This is done as before regarding 2 described.

The bus states DF2 . DF3 can from other subscriber stations, for example the subscriber stations 10 . 30th to signal an error, for example in the acknowledgment in the end field 456 at the end of the frame 45 , are overwritten. This overwriting can be related to the bus state DF3 ("Negative dominant"), however, can only be recognized if by the relevant transceiver 12 22 . 32 in the receiving section also the bus states DF1 ("Positive dominant"), DF3 ("Negative dominant") are distinguishable.

Each of the transmitting / receiving devices thus switches 22 . 32 in the present exemplary embodiment in a first operating mode between the two bus states DF1 . DF3 for the message 5 if from the message 5 Arbitration phase or first phase data 456 . 451 . 452 are to be sent. In addition, each of the transmitting / receiving devices switches 22 . 32 in a second operating mode with the three different bus states DF1 . DF2 . DF3 for the message 5 if from the message 5 Data of the data phase or second phase 453 . 454 . 455 are to be sent.

Each of the transmitting / receiving devices 22 . 32 thus switches between up to three different bus states DF1 . DF2 . DF3 to the message 5 or the frame 45 to send. Here are the two bus states DF1 . DF2 symmetrical to each other. Of course, more than the three bus states mentioned are possible, for example by adding at least one additional bus state DF1 . DF2 . DF3 is introduced with a level that, for example, between the level of the bus states DF1 . DF2 and the level of the bus state DF3 lie. Additionally or alternatively, it is conceivable that at least one bus state with levels is introduced that is, for example, above the level of the bus states DF1 . DF2 and the level of the bus state DF3 lie.

By expanding the bus states or symbols from two to at least three by means of coding and decoding, more data can be transmitted per time at a given transmission frequency. This leads to an increase in the baud rate, as previously mentioned.

Here, all three bus states can DF1 . DF2 . DF3 at least for sending the data field 454 used. There is also a use of the three bus states DF1 . DF2 . DF3 also in the fields 453 . 455 possible as previously described. The bit rate can thus be increased by coding.

In addition, with the design of the transmitting / receiving devices 22 . 32 the same advantages are achieved in the present exemplary embodiment as described above with reference to the first exemplary embodiment.

According to a second embodiment, the frequency of the signals 412 . 422 reduced. As a result, an improvement in the EMC behavior can be achieved. The coding described in more than two bus states enables the bit rate to be kept constant despite the lower frequency.

According to a third exemplary embodiment, the second bus state DF2 a negative differential voltage VDIFF, but a lower bus level than the first bus state DF1 , In this case, the second bus state can also DF2 safe through the first bus state DF1 be overwritten. So the first and second bus state DF1 . DF2 in at least part of the fields 451 . 452 . 456 or usable in the entire arbitration phase. In addition, even with such three bus states DF1 . Df2 . DF3 In the data phase, the coding described above in more than two bus states increases the bit rate or keeps the bit rate constant despite the lower frequency.

The arbitration in all of the exemplary embodiments and their modifications compared to classic CAN and CAN FD therefore takes place unchanged in accordance with the CSMA / CR method. During the arbitration, there are still only two bus states, "positive dominant" and "recessive". As a result, the effort for the introduction and conversion to the bus system according to the invention is reduced. Suitable measures can also enable the CAN FE frames to coexist with the CAN and / or CAN FD frames or a tolerance of the CAN and CANFD subscriber stations to the CAN FE frames.

1. a) Übernahme und ggf. Anpassung bewährter Eigenschaften, die für die Robustheit und Anwenderfreundlichkeit von CAN und CAN FD verantwortlich sind, insbesondere Rahmenstruktur mit Identifier und Arbitrierung nach dem CSMA/CR-Verfahren,
2. b) Steigerung der Netto-Datenübertragungsrate auf etwa 10 Megabit pro Sekunde,
3. c) Anheben der Größe der Nutzdaten pro Rahmen auf eine größere Länge als bei CAN oder CAN FD, insbesondere maximal 4kbyte,
4. d) Optional: Vollständiger oder teilweiser Verzicht auf das Versenden von Fehlerrahmen (Error Frames) bei Erkennen von Fehlern.

The previously described new development "CAN FE" therefore has the following properties in comparison to CAN or CAN FD:

1. a) Adopting and, if necessary, adapting proven properties that are responsible for the robustness and user-friendliness of CAN and CAN FD, in particular frame structure with identifier and arbitration according to the CSMA / CR process,
2. b) increasing the net data transfer rate to approximately 10 megabits per second,
3. c) increasing the size of the user data per frame to a greater length than in the case of CAN or CAN FD, in particular a maximum of 4 kbytes,
4. d) Optional: Complete or partial waiver of sending error frames when errors are detected.

All previously described configurations of the bus system 1 , the subscriber stations 10 . 20th . 30th and that of the subscriber stations 10 . 20th . 30th executed methods can be used individually or in all possible combinations. In particular, all features of the previously described exemplary embodiments and / or their modifications can be combined as desired. In addition or as an alternative, the following modifications are particularly conceivable.

The bus system described above 1 According to the exemplary embodiments, a bus system based on the CAN protocol is used. The bus system 1 According to the exemplary embodiments, however, there can also be another type of communication network in which data can be transmitted serially at two different bit rates. It is advantageous, but not an essential requirement, for the bus system 1 Exclusive, collision-free access by a subscriber station at least for certain periods of time 10 . 20th . 30th is guaranteed on a common channel.

The number and arrangement of the subscriber stations 10 . 20th . 30th in the bus system 1 the exemplary embodiments are arbitrary. In particular, the subscriber station 10 in the bus system 1 omitted. It is possible that one or more of the subscriber stations 20th or 30th in the bus system 1 available.

Claims (11)

Subscriber station (20; 30) for a serial bus system (1), with a transmitting / receiving device (22; 32) for the serial transmission of a message (5) on a bus line (3) to at least one further subscriber station (10; 20; 30) of the bus system (1) and / or for the serial reception of a message ( 5) from the bus line (3), wherein the transmitting / receiving device (22; 32) is designed to switch between a first operating mode and a second operating mode for serial transmission and / or for serial reception of the message (5), The transmitting / receiving device (22; 32) is designed in the first operating mode to generate a first and a second data state as a bus state (DF1, DF3) with different bus levels for two bus wires (41, 42) of the bus line (3), and wherein the transmitting / receiving device (22; 32) is configured in the second operating mode, in addition to the first and second data states, a third data state as bus state (DF1, DF2, DF3) with a bus level for the two bus wires (41, 42) To generate bus line (3), which differs from the bus levels for the first and second data state (DF1, DF2). Participant station (20; 30) after Claim 1 , the bus states (DF1, DF2) for the first and second data states being symmetrical to one another. Participant station (20; 30) after Claim 1 or 2 , wherein the transceiver (22; 32) is configured to generate the bus state (DF2) for the second data state by driving the bus levels for the two bus wires (41, 42) weaker than the bus state (DF1) for the first data state . Subscriber station (20; 30) according to one of the preceding claims, wherein the transceiver (22; 32) is designed to generate the bus states (DF1 to DF3) in such a way that the bus state (DF1) for the first data state and the bus state (DF2) for the second Data state as well as the bus state (DF3) for the third data state can overwrite. Subscriber station (20; 30) according to one of the preceding claims, wherein the transceiver (22; 32) is configured to switch to the first operating mode if the message (5) is to be used to transmit data of a first phase (456; 451; 452) which is to be transmitted at a first bit rate are and wherein the transceiver (22; 32) is configured to switch to the second mode of operation if the message (5) is to be used to transmit data of a second phase (453; 454; 455) which is to be transmitted at a second bit rate which is faster than the first bit rate. Participant station (20; 30) after Claim 5 , wherein the transceiver (22; 32) is configured to switch to the first operating mode or the second operating mode according to a predetermined coding when the data of the second phase (453; 454; 455) comes from the message (5) are sending. Subscriber station (20; 30) according to one of the preceding claims, wherein the transmitting / receiving device (22; 32) is designed to switch only into the second mode of operation for transmitting data if for the subscriber station (20; 30) for a predetermined one Exclusive, collision-free access to the bus line (3) of the bus system (1) is guaranteed. Subscriber station (20; 30) according to one of the preceding claims, wherein the transceiver (22; 32) is designed to transmit the data for the first and second data states (DF1, DF2) in the first operating mode with the same bus level to the bus line (3) to send as in the second mode. Subscriber station (20; 30) according to one of the preceding claims, wherein the message (5) has a data field (454) with a variable length, the variable length being between 1 byte and 4096 bytes. Bus system (1), with a bus line (3), and at least two subscriber stations (10; 20; 30) which are connected to one another via the bus line (3) in such a way that they can communicate with one another in series, wherein at least one of the at least two subscriber stations (10; 20; 30) is a subscriber station (20; 30) according to one of the preceding claims. Method for sending a message (5) in a serial bus system (1), the method comprising the step: serial transmission, with a transmission / reception device (22; 32) of a subscriber station (20; 30) of the bus system (1), a message (4; 5) on a bus line (3) of the bus system (1), the transmission / Receiving device (22; 32) can be configured in addition to the serial reception of a message (5) from the bus line (3), wherein the transceiver (22; 32) switches between a first operating mode and a second operating mode for serial transmission, The transmitter / receiver device (22; 32) in the first operating mode generates a first and a second data state each as a bus state (DF1, DF3; DF1, DF2) with different bus levels for two bus wires (41, 42) of the bus line (3), and wherein the transceiver (22; 32) in the second operating mode, in addition to the first and second data status, has a third data status as bus status (DF1, DF2, DF3) with a bus level for the two bus cores (41, 42) of the bus line (3 ) that differs from the bus levels for the first and second data states (DF1, DF2).

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