Subscriber station for a serial bus system and method for communication with differential signals in a serial bus system

Abstract

A subscriber station (10; 30) for a serial bus system (1) and a method for transmitting a message (45) with differential signals (CAN_H, CAN_L) in a serial bus system are provided. The subscriber station (10; 30) has a transmitting / receiving device (12) for transmitting a digital transmit signal (TxD) as an analog differential signal (CAN_H, CAN_L) to a bus (40) of the bus system (1) in order to transmit a message (45; 46; 47) to at least one other subscriber station (10; 20; 30) of the bus system (1) and / or for receiving an analog signal (CAN_H, CAN_L; VDIFF) from the bus (40), a switching module (18) for switching off a bus bias voltage (U2; U3) for the bus (40) during a predetermined detection period (T_M1; T_M1, T_M2; T_M3), a bus voltage detection module (14) for detecting the bus voltage (Vcm) received by the transmitting / receiving device (12) from the bus (40) during the predetermined detection period (T_M1; T_M1, T_M2;T_M3), and a bus voltage setting module (16) for setting the bus bias voltage (U2; U3) to a voltage value resulting from a detection performed by the bus voltage detection module (14) during the predetermined detection period (T_M1; T_M1, T_M2; T_M3);

Description

The present invention relates to a subscriber station for a serial bus system and to a method for communication with differential signals in a serial bus system.Prior ArtFor communication in serial bus systems with differential signals, CAN bus systems are used, for example. Currently, classic CAN and / or CAN FD are used for the communication between devices in vehicles and / or in other technical devices, both of which are standardized in the international standard ISO11898-1:2015. The devices form subscriber stations on the bus, which are also called nodes. Each subscriber station has at least one transmitting / receiving device, which is also called a transceiver.CAN FD is currently often used with 2 Mbit / s data bit rate and 500 kbit / s arbitration bit rate. So-called CAN SIC transmitting / receiving devices make it possible to use CAN FD with up to 8 Mbit / s. For higher data rates of currently up to 20 Mbit / s, CAN XL is now available.At present, in CAN bus systems for the transmitting / receiving devices (transceivers), a voltage source of Vcc=5 V is used in order to generate the different voltage levels for differential signals on the bus. The signals signal the data to be exchanged serially.For cost reduction, it is considered to use a power source of Vcc=3.3 V for the transmitting / receiving devices. Such a lowering of the supply voltage would be advantageous since the voltage of 3.3 V is used in many microcontrollers of today. In addition, many other modules can also be supplied with this voltage.However, it is problematic that at present a large number of devices that can be used on the CAN bus and have a voltage supply of 5 V are already present. Therefore, the lowering of the supply voltage from 5 V to 3.3 V offers the desired advantage only if mixed operation on the bus is possible. In this case, 5V subscriber stations (5V nodes) and 3.3V subscriber stations (3.3V nodes) must be able to communicate simultaneously on a bus in any desired number.It should be taken into account here that the present CAN bus has a voltage of Vcc / 2, that is to say 2.5 V on average on account of the differential signals CAN_H, CAN_L. This is achieved by each bus subscriber station attempting, via a standardized resistor network, by means of a current source to keep the bus more or less exactly at 2.5 V. The bus voltage essentially follows the node voltage (voltage at the subscriber station) which is lowest, i.e. is typically slightly below 2.5 V.During transmission, a CAN subscriber station (node), more precisely its transmitting / receiving device, can switch between a dominant state and a recessive state. For the dominant state, it drives the CAN_H level to about 3.5 V (Vcc diode voltage - losses) and the CAN_L level to about 1.5 V (diode voltage across GND). The difference between CAN_H level and CAN_L level is then in a range of 2 V. The international standard ISO11898-1:2015 requires a minimum of 1.5 V. The transition from the review to the dominant state or back takes place as symmetrically as possible about the virtual zero line, which is at Vcc / 2. As a result, the sum of the levels of CAN_H and CAN_L remains as much as possible at 5 V.A great problem is that smaller deviations in the mV range already result in distinct electromagnetic emissions which cause EMC interference (EMC=electromobic compatibility) of other electrical devices. Therefore, there are specifications for maximum permissible electromagnetic emissions to be met by each transmitting / receiving device (transceiver). However, these electromagnetic emissions requirements present a very great challenge.The challenges are all the greater in mixed operation if at least one subscriber station with a transmitting / receiving device (transceiver) is present on the bus, which device drives different voltage levels for CAN_H and CAN_L in the dominant state than transmitting / receiving devices (transceiver) of other subscriber stations. Reasons for this are as follows.A 3.3V CAN bus operates the same as the 5V CAN bus except that the voltages on the bus are different. A 3.3V node (subscriber station) can bring the signal CAN_H to approximately 3V and the signal CAN_L to significantly below 1V for the dominant state on the bus, by eliminating the diode voltage of a diode of the transmitting / receiving device (transceiver) in terms of circuitry. As a result, the specified minimum level difference of 1.5 V can be exceeded even in the case of a 3.3V CAN bus system.A special feature in mixed operation is that a 5V node in the recessive phase sets the bus to 2.5 V, while a 3V node targets about 1.65 V on the bus. By raising the CAN_L voltage at 3.3V CAN in the direction 1V, the voltage in the recessive state can be raised to approximately 1.9 V. However, there remains a difference of about 500-600 mV between the 5V and 3.3V nodes. The bus, in such a configuration, takes a voltage anywhere between 1.9 V and 2.5 V and a current flows constantly towards the 3.3 V node, but in the range of a few microamperes.However, if a subscriber station (node) now starts to transmit and goes into the dominant state, the subscriber station (node) does not do so from "its" zero line, but rather from that of the mixed mode. As a result, the sum of the levels of CAN_H and CAN_L changes at the time of shifting, and again at the time of downshifting.This will predictably result in high EMC emissions. Thus, a mixing operation is not possible as easily.Disclosure of the InventionIt is therefore an object of the present invention to provide a subscriber station for a serial bus system and a method for communication with differential signals in a serial bus system, which solve the aforementioned problems. In particular, a subscriber station for a serial bus system and a method for communication with differential signals in a serial bus system are to be provided, which are as inexpensive as possible and thus enable reliable and as free of errors and low-emission communication as possible on a bus to which subscriber stations are also connected, whose transmitting / receiving devices are designed to generate different voltage levels on the bus than the subscriber station.The object is achieved by a subscriber station for a serial bus system having the features of claim 1. The subscriber station has a transmitting / receiving device for transmitting a digital transmission signal as an analog differential signal onto a bus of the bus system in order to transmit a message to at least one other subscriber station of the bus system, and / or for receiving an analog signal from the bus, a switching module for switching off a bus bias voltage for the bus during a predetermined detection time period, a bus voltage detection module for detecting the bus voltage received by the transmitting / receiving device from the bus during the predetermined detection time period, and a bus voltage setting module for setting the bus bias voltage to a voltage value which results from a detection carried out by the bus voltage detection module during the predetermined detection time period.The described subscriber station thus solves the problem that, above all, the conventional subscriber stations do not expect any extraneous voltage levels on the bus from their design. The previously described subscriber station, unlike conventional subscriber stations, is downwardly compatible and enables communication on the same bus at different voltage levels.The described subscriber station (node) ensures that the zero line is brought to the level required by the associated subscriber station before the transmission of a dominant state. This level is about 1.9 volts for a 3.3 volt subscriber station and about 2.5 volts for a 5 volt subscriber station. Of course, this applies not only to the zero line before transmission of a dominant state, but also between such states. As a result, the emissions which generate the problems with respect to electromagnetic compatibility (EMC) can be significantly reduced and at best minimized in the phase in which the subscriber station, more precisely its transmitting / receiving device, transmits.The described configuration of the subscriber station is advantageous above all during the arbitration phase in which the subscriber stations negotiate with one another which of the subscriber stations has exclusive access to the bus in the following data phase and is thus allowed to send their message. The reason for this is that large scrambling already prevails during the arbitration phase, since all user stations ready to transmit are in the dominant state here. The transmitting / receiving device described ensures that it transfers the bus level to the level desired by it without too great a voltage jump, i.e. "soft", if it recognizes at the end of the arbitration phase that it is allowed to transmit. The same applies after transmission in the data phase if the described transmitting / receiving device switches back from the data phase into the arbitration phase again.In this way, the described subscriber station enables mixed operation of subscriber stations with different voltages, in particular of 3.3V subscriber stations and 5V subscriber stations. As a result, the subscriber station can provide a cost saving for the bus system and at the same time still enable low-emission and fault-free operation of the bus system.As a result, the described subscriber station is extremely resource-saving and cost-effective.Overall, the described subscriber station can therefore not only implement the communication in the bus system between other subscriber stations with the (high) bit rates required for the respective communication standard even in the described mixed mode, but is also designed in such a way that the transmittable bit rate is not reduced by errors in the communication.Advantageous further embodiments of the subscriber station are described in the dependent claims.The subscriber station may have a sensing module control block for controlling the bus voltage sensing module such that during the predetermined sensing period of time there is a recessive state on the bus rewritable from a dominant state on the bus.The subscriber station may have a sensing module control block for controlling the bus voltage sensing module such that during the predetermined sensing period on the bus a transition from a dominant state to a recessive state takes place which is rewritable from a dominant state on the bus, wherein the transition from the dominant state to a recessive state is in particular an SIC state.The subscriber station may have a sense module control block for controlling the bus voltage sense module such that during the predetermined sense period the end of the arbitration phase takes place and a dominant state prevails on the bus.It is conceivable that the bus voltage detection module also has a switch and a memory element, wherein the detection module control block is configured to control the switch for connecting the memory element to the bus in order to detect the bus voltage received by the transmitting / receiving device from the bus.The previously described subscriber station can also have a bus voltage provision module for providing two different bus biases, wherein the bus voltage setting module is configured to set one of the two different bus biases for the transmitting / receiving device on the basis of the bus voltage detected by the bus voltage detection module during the predetermined detection period.Optionally, the bus voltage providing module includes a voltage divider having six resistors for providing the two different bus biases.Optionally, the bus voltage providing module comprises a semiconductor having three band gap derivatives for providing the two different bus biases.The bus voltage setting module may include a changeover switch and a setting module control block for controlling the position of the changeover switch on the basis of the bus voltage detected by the bus voltage detection module during the predetermined detection period.The previously described subscriber station may be configured to negotiate with the other subscriber stations of the bus system during a first communication phase which of the subscriber stations has exclusive access to the bus in the following second communication phase and is thus allowed to send their message.The transmitting / receiving device can be configured to generate the analog differential signal in a first communication phase of the message with a different physical layer than in a second communication phase.In one configuration, the previously described subscriber station also has an event detection module for detecting an event after which the bus voltage detection module has to carry out a detection of the bus voltage present on the bus, wherein the detection module control block is configured to control the bus voltage detection module for detecting the bus voltage present on the bus during the predetermined detection time period after the event detection module has detected the event.Here, the event may be a predetermined number of directly consecutive re-intensive bits at the end of a frame sent over the bus for the message.The event can be that at the end of the first communication phase the subscriber station is determined which in the following second communication phase has the exclusive access to the bus and is thus allowed to send its message.The previously described subscriber station may also have a bus voltage holding module for holding the bus voltage detected by the bus voltage detection module on the bus, and optionally also having a storage element which is arranged between the bus voltage holding module and the bus voltage setting module for storing a voltage at the output of the bus voltage detection module.The previously described subscriber station can also have a bus voltage driver for driving the bus bias voltage for the transmitting / receiving device set by the bus voltage setting module onto the bus.In one embodiment, the previously described subscriber station additionally has a communication control device for controlling the communication in the bus system and for generating the transmission signal, wherein the subscriber station is designed for the communication in a bus system in which exclusive, collision-free access of a subscriber station to the bus of the bus system is ensured at least temporarily.At least one previously described subscriber station can be part of a bus system which additionally has a bus and in which at least two subscriber stations are connected to one another via the bus in such a way that they can communicate with one another in series.The aforementioned object is also achieved by a method for communication with differential signals in a serial bus system having the features of claim 19. The method is carried out with a subscriber station of the bus system, which has a transmitting / receiving device for transmitting a digital transmission signal as an analog differential signal onto a bus of the bus system, in order to transmit a message to at least one other subscriber station of the bus system, and / or for receiving an analog signal from the bus, wherein the method has the steps of switching off, with a switching module, a bus bias voltage for the bus during a predetermined detection time period, detecting, with a bus voltage detection module, the bus voltage received by the transmitting / receiving device from the bus during the predetermined detection time period, and setting, with a bus voltage setting module, the bus bias voltage to a voltage value which results from a detection carried out by the bus voltage detection module during the predetermined detection time period.The method provides the same advantages as mentioned above with respect to the subscriber station.Further possible implementations of the invention also include combinations, not explicitly mentioned, of features or embodiments described above or below with respect to the exemplary embodiments. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.DRAWINGSThe invention is described in more detail below with reference to the accompanying drawing and with reference to exemplary embodiment(s). The following are shown: FIG. 1 shows a simplified block diagram of a bus system according to a first exemplary embodiment; FIG. 2 shows a diagram for illustrating the structure of a message which can be sent by a first subscriber station of the bus system according to the first exemplary embodiment; FIG. 3 shows a time profile of a digital transmission signal during operation of the bus system at the first and / or second subscriber station, which is connected to the same bus of the bus system by at least one first subscriber station; FIG. 4 shows a time profile of bus signals CAN_H and CAN_L at the second subscriber station according to the first exemplary embodiment; FIG. 5 shows a time profile of a differential voltage VDIFF of the bus signals CAN_H and CAN_L in the first and second subscriber stations according to the first exemplary embodiment; FIG. 6 shows a time profile of a digital reception signal which the first or second subscriber station generates from a signal received from the bus, which signal is based on the transmission signal from FIG. 3 ; FIG. 7 shows a temporal profile of bus signals CAN_H and CAN_L, which can be generated on the bus by the first subscriber station according to the first exemplary embodiment on the basis of the transmission signal from FIG. 3 ; FIG. 8 shows an example of a temporal profile of a digital transmission signal which is to be converted in an arbitration phase (SIC operating mode of a transmission module) into bus signals CAN_H, CAN_L for a bus of the bus system from FIG. 1 ; FIG. 9 shows the time profile of the bus signals CAN_H, CAN_L when changing between a recessive bus state to a dominant bus state and back to the recessive bus state, which are sent to the bus in the arbitration phase (SIC operating mode) on the basis of the transmission signal from FIG. 8 ; FIG. 10 shows a circuit diagram of a subscriber station of the bus system according to the first exemplary embodiment; FIG. 11 shows a circuit diagram of a subscriber station of the bus system according to a second exemplary embodiment; and FIG. 12 shows a circuit diagram of a subscriber station of the bus system according to a third exemplary embodiment.In the figures, identical or functionally identical elements are provided with the same reference numerals, unless otherwise indicated.DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows a bus system 1, which can be, for example, at least in sections a CAN bus system, a CAN-FD bus system, etc. The bus system 1 can be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in a hospital, etc.Even if bus system 1 is described below with reference to CAN bus systems, bus system 1 is not limited to CAN bus systems, however.In FIG. 1, the bus system 1 has a multiplicity of subscriber stations 10, 20, 30, which are each connected to a bus 40 or bus line having a first bus wire 41 and a second bus wire 42. In a CAN bus system, bus cores 41, 42 may also be referred to as CANH and CANL for conducting signals CAN_H, CAN_L on bus 40.Messages 45, 46, 47 in the form of signals can be transmitted between the individual subscriber stations 10, 20, 30 via the bus 40. The subscriber stations 10, 20, 30 are, for example, control units or display devices of a motor vehicle.As shown in FIG. 1, the subscriber stations 10, 30 each have a communication control device 11 and a transmitting / receiving device 12. At least one of the subscriber stations 10, 20, 30 uses a supply voltage of 3.3 V and at least one subscriber station 10, 20, 30 uses a supply voltage of 5 V. For illustration, the following embodiments show an example of a network or bus system 1, in which the subscriber station 20 has a supply voltage of 5 V and the subscriber stations 10 and 30 have a supply voltage of 3.3 V. Other constellations are also conceivable.The subscriber station 20 has a communication control device 21 and a transmitting / receiving device 22.The transmitting / receiving devices 12 of the subscriber stations 10, 30 and the transmitting / receiving device 22 of the subscriber station 20 are each connected directly to the bus 40, even if this is not shown in FIG. 1.The communication control devices 11, 21 each serve to control a communication of the respective subscriber station 10, 20, 30 via the bus 40 with at least one other subscriber station of the subscriber stations 10, 20, 30, which are connected to the bus 40.The communication controller 11 creates and reads first messages 45, 47, which are, for example, modified CAN messages 45, 47. In this case, the modified CAN messages 45, 47 are constructed in particular on the basis of the CAN XL format. The transmitting / receiving device 12 serves to transmit and receive the messages 45, 47 from the bus 40. the transmitting module 121 receives a digital transmission signal TxD produced by the communication control device 11 for one of the messages 45, 47 and converts this into signals on the bus 40, as described in more detail with reference to FIGS. 3, 4 and 7. The digital transmission signal TxD can be a pulse-width-modulated signal at least temporarily or in sections. The receiving module 122 receives signals transmitted on the bus 40 corresponding to the messages 45 to 47 and generates therefrom a digital received signal RxD, an example of which is shown in FIG. 6. The receiving module 122 transmits the received signal RxD to the communication controller 11.In addition, the communication control device 11 can optionally be configured to generate and read second messages 46, which are CAN FD messages or CAN SIC messages 46, for example. The transmitting / receiving device 12 can be designed accordingly.The communication control device 21 can be embodied as a conventional CAN controller according to ISO 11898-1:2015, i.e. as a CAN FD-tolerant classic CAN controller or a CAN FD controller or a CAN SIC controller. The communication control device 21 generates and reads second messages 46, for example CAN FD messages or CAN SIC messages. The transmitting / receiving device 22 serves to transmit and receive the messages 46 from the bus 40. the transmitting module 221 receives a digital transmission signal TxD created by the communication control device 21 and converts this into signals for a message 46 on the bus 40, as described in more detail with reference to FIGS. 3 and 4. The receiving module 222 receives signals transmitted on the bus 40 corresponding to the messages 45 to 47 and generates therefrom a digital received signal RxD, an example of which is shown in FIG. 6. The transmitting / receiving device 22 may be implemented as a conventional CAN FD transceiver or CAN SIC transceiver.Proven properties are adopted for transmitting messages 45, 46, 47 using CAN SIC or CAN XL, which are responsible for the robustness and user-friendliness of CAN and CAN FD, in particular frame structure with identification and arbitration according to the known CSMA / CR method, as described in more detail below.The two subscriber stations 10, 30 can be used to form and then transmit messages 45, 46, 47 with different CAN formats, in particular the CAN FD format or the CAN SIC format or the CAN XL format, and to receive such messages 45, 46, 47. This is described in more detail below for a message 45.FIG. 2 shows a frame 450, which is in particular a CAN XL frame, for the message 45 as provided by the communication control device 11 for the transmitting / receiving device 12 to transmit onto the bus 40. Here, the communication controller 11 creates the frame 450 in the present embodiment as compatible with CAN FD. Alternatively, frame 450 is compatible with any follow-up standard for CAN FD.According to FIG. 2, the frame 450 for the CAN communication on the bus 40 is divided into different communication phases 451, 452, namely an arbitration phase 451 (first communication phase) and a data phase 452 (second communication phase). After a start bit SOF, the frame 450 has an arbitration field 453, a control field 454, a first switching field 455, a data field 456, a checksum field 457, a second switching field 458 and a frame termination field 459 in which a flag EOF (EOF=End of Frame) is present. The checksum field 457, the second switching field 458 and the frame termination field 459 form a frame end phase 457, 458, 459 of the frame 450. In the frame termination field 459, there may be an acknowledgement field (ACK= Ack) not shown in the figures.In contrast to the frame 450 of FIG. 2, no changeover fields 455, 458 are present in a CAN FD frame which the subscriber station 20 uses for the second message 46.For all the aforementioned CAN versions, it applies that in arbitration phase 451, with the aid of an identifier (ID) in arbitration field 453, it is negotiated bit by bit between subscriber stations 10, 20, 30, which subscriber station 10, 20, 30 wishes to send message 45, 46, 47 with the highest priority and therefore receives exclusive access to bus 40 of bus system 1 for the next time to send in subsequent data phase 452. In arbitration phase 451, a physical layer is used as in CAN and CAN-FD. The physical layer corresponds to the physical layer or layer 1 of the known OSI (open systems interconnection) model.During phase 451, the known CSMA / CR method is used, which allows simultaneous access of the subscriber stations 10, 20, 30 to the bus 40 without destroying the message 45, 46, 47 with a higher priority. As a result, further bus subscriber stations 10, 20, 30 can be added to the bus system 1 in a relatively simple manner, which is very advantageous.The result of the CSMA / CR method is that there must be so-called recessive states on the bus 40, which can be overwritten by other subscriber stations 10, 20, 30 with dominant levels or dominant states on the bus 40. In the recessive state, high-impedance conditions prevail at the individual subscriber station 10, 20, 30, which results in longer time constants in combination with the parasites of the bus circuit. This leads to a limitation of the maximum bit rate of the present CAN-FD physical layer to currently approximately 2 megabits per second in real vehicle use.At the end of arbitration phase 451, data phase 452 is entered. In the case of CAN XL, the switchover takes place with the aid of the first switchover field 455 of FIG. 2.In the data phase 452, in the case of CAN XL, the payload data of the CAN XL frame 450 or of the message 45 from the data field 456 and also the checksum field 457 and a part of the second changeover field 458 are transmitted in addition to a part of the first changeover field 455. In the case of CAN FD, the payload data of the CAN FD frame or of the message 46 is transmitted from the data field 456 and also the checksum field 457.At the end of the data phase 452, the system switches back to the arbitration phase 451. In the case of CAN XL, the switchover takes place with the aid of the second switchover field 458 of FIG. 2.A transmitter of the message 45 only starts transmitting bits of the data phase 452 onto the bus 40 or only when the subscriber station 10 as the transmitter has gained arbitration and the subscriber station 10 as the transmitter thus has an exclusive access to the bus 40 of the bus system 1 for transmission.In the end of frame field EOF, a bit sequence is provided which marks the end of frame 450. Thus, the end field bit sequence (EOF) serves to identify the end of frame 450. The end field (EOF) provides that a number of 7 re-intensive bits is transmitted at the end of frame 450. Together with an optionally present ACK delimiter in the not shown acknowledgment field, a number of 8 re-intensive bits is transmitted at the end of frame 450. The mentioned bit sequence of recessive bits are bit sequences that cannot occur within frame 450. As a result, the end of the frame 450 can be reliably detected by the subscriber stations 10, 30.Starting from a time or a time t1, more precisely beginning from the time t1, the subscriber station 10 carries out a detection of the bus potential or the bus voltage present on the bus 40 for a time duration T_M1. The detection is performed after an event E1 has occurred. Event E1 is that a predetermined number of directly consecutive re-intensive bits have occurred at the end of frame 450, more specifically in the end field (EOF).Optionally, starting from a time t2, more precisely beginning from the time t2, the subscriber station can carry out a detection of the bus potential or of the bus voltage present on the bus 40 for a time duration T_M2. The detection is performed after an event E2 has occurred. Event E2 is that at the end of the first communication phase the subscriber station is determined which in the following second communication phase has the exclusive access to the bus and is thus allowed to send his message.This acquisition(s) or measurement(s) are described below with reference to the figures.After the end field (EOF) having 7 bits, an inter frame space (IFS) follows in the frame 450, which is not shown in FIG. 2. This interframe spacing (IFS) is designed in CAN FD to correspond to ISO11898-1:2015. The inter frame space (IFS) has at least 3 bits.Incidentally, the fields and bits mentioned are known from ISO11898-1:2015 and are therefore not described in more detail here.Thus, in the arbitration phase 451, the subscriber stations 10, 30 partially use, in particular up to the FDF bit (inclusive), a format known from CAN / CAN-FD according to ISO11898-1:2015 as the first communication phase. However, in comparison with CAN or CAN FD, an increase in the net data transmission rate, in particular to more than 10 megabits per second, is possible in the data phase 452 as the second communication phase. In addition, it is possible to increase the size of the payload per frame, in particular to approximately 2 kbytes or any other value.FIGS. 3, 5 and 6 illustrate, as an example, the signals which are generated at the subscriber stations 10, 20, 30 during operation of the bus system 1. FIG. 4 illustrates, as an example, the signals which are transmitted from the subscriber station 20 to the bus 40 during operation of the bus system 1. As already mentioned, the subscriber station 20 uses a supply voltage of 5 V. Fig. 7 shows the bus signals which each of the subscriber stations 10, 30 generates instead of the bus signals shown in Fig. 4. As already mentioned, the subscriber stations 10, 30 use a supply voltage of 3.3 V.During operation of the bus system 1, each of the transmission modules 121, 221 of FIG. 1 can convert a transmission signal TxD of the associated communication control device 11 serially into corresponding signals CAN_H, CAN_L for CAN or CAN FD for the bus cores 41, 42 and transmit these signals at the connections for CAN_H and CAN_L to the bus 40. The respective communication control device 11, 21 transmits the transmission signal TxD of FIG. 3 over the time t (serial) to the associated transmission module 121, 221 as shown in FIG. 1.As shown by way of example in FIG. 3, the transmit signal TxD has the voltage states H (high=high) and L (low=low) with a corresponding voltage U. The individual bits of the signal TxD have a bit time t_bt 1, as shown in FIG. 3 for the arbitration phase 451. For CAN FD and CAN XL, the bits of the signal TxD may be transmitted in the data phase 452 with a shorter bit time t_bt 2, as illustrated in FIG. 4.The sequence of the states H, L of the transmission signal TxD of FIG. 3 and the states 401, 402 resulting therefrom for the signals CAN_H, CAN_L in FIG. 4 and the resulting curve of the voltage VDIFF of FIG. 5 serves only to illustrate the function of the subscriber station 10.According to the example of FIG. 4, the signals CAN_H and CAN_L have the dominant and recessive bus levels or bus states 401, 402, as known from CAN, at least in the arbitration phase 451. Since the subscriber station 20 uses a supply voltage of 5 V, it drives the CAN_H level to approximately 3.5 V and the CAN_L level to approximately 1.5 V for the dominant state 401, as shown in FIG. 4. The regenerative state 402 is set at 2.5 V, which is equal to the bus center voltage Vcm=2.5 V.As shown in FIG. 5 for the differential voltage VDIFF=CAN_H-CAN_L on the bus 40, the difference between CAN_H level and CAN_L level for the dominant state 401 is then in a range of 2 V.The receiving modules 122, 222 form a received signal RxD from signals CAN_H and CAN_L received from the bus 40, which are shown in FIG. 4, and from the differential voltage VDIFF of FIG. 5, respectively. For generating the digital received signal RxD of FIG. 6, the respective receiving module 122, 222 samples the signal VDIFF empfangene by the bus 40 or at least one of the signals CAN_H, CAN_L at sampling points AP according to FIG. 4 and FIG. 5, as is known. The receive signal RxD is shown in FIG. 6 without propagation delay. The receiving module 122 passes on this received signal RxD to the associated communication control device 11, 21, as shown in FIG. 1.In contrast to FIG. 4, FIG. 7 shows the signals CAN_H and CAN_L which the subscriber stations 10, 30 generate on the bus 40 in the arbitration phase 451 and the data phase 452. At least in the arbitration phase 451, the dominant and recessive bus levels or bus states 401, 402 are used, as already shown in FIG. 4. Since the subscriber stations 10, 30 use a supply voltage of 3.3 V, they drive the CAN_H level to approximately 2.9 V and the CAN_L level to approximately 0.9 V for the dominant state 401, as shown in FIG. 7. The regenerative state 402 is set at 1.9 V, which is equal to the bus center voltage Vcm=1.9 V. In the data phase 452, a different physical layer 452_P is usable for CAN XL than the physical layer 451_P in the arbitration phase 451. As a result, the CAN_H levels may be driven to values for the states LV 1, LV 0, as shown in FIG. 7. In arbitration phase 451, a physical layer is used as in CAN and CAN-FD. The physical layer corresponds to the physical layer or layer 1 of the known OSI (open systems interconnection) model.For the transmission signal TxD of FIG. 3, the transmission module 121 generates the signals CAN_H, CAN_L in FIG. 7 for the bus cores 41, 42 in such a way that the state LV 0 forms for a state LW (Low=Low). In addition, state LV 1 is formed for a state HI (High=High).In order to increase the data rate for CAN XL, the transmitting / receiving devices 12 can be designed for CAN SIC.As shown in more detail in FIGS. 8 and 9, the transmission module 121 generates the signals CAN_H, CAN_L according to FIG. 9 for the bus cores 41, 42 with a bus center voltage Vcm_sic=1.9 V at CAN SICfor the transmission signal TxD of FIG. 8 and in such a way that a state 403 (sic) additionally exists. State 403 (SIC) may be of different lengths, as shown with state 403_ 0 (sic) in the transition from state 402 (rec) to state 401 (dom) and state 403_ 1 (sic) in the transition from state 401 (dom) to state 402 (rec). State 403_ 0 (sic) is shorter in time than state 403_ 1 (sic). In order to generate signals according to FIG. 9, the transmission module 121 is switched into an SIC mode (SIC mode).The passing through the short sic state 403_ 0 is not required in the CiA 610- 3, and the state depends on the type of implementation. The time duration of the "long" state 403_ 1 (sic) is specified as t_sic< 530ns for CAN-SIC as well as for SIC mode in CAN-XL, starting with the rising edge on the transmit signal TxD of FIG. 5.Starting from a time or a time t3, more precisely beginning from the time t3, after an event E3 has occurred, the subscriber station 10 carries out a detection of the bus potential or the bus voltage which is / is present on the bus 40 for a time duration T_M3. Event E 3 is that state 401 (dom) is exited or is switched from state 401 (dom) to state 403 (sic).In the "long" state 403_ 1 (sic), the transmission module 121 is intended to adapt the impedance between the bus cores 41 (CANH) and 42 (CANL) as well as possible to the characteristic characteristic characteristic characteristic characteristic characteristic characteristic characteristic impedance Zw of the bus line used. Here, Zw=100 Ohm or 120 Ohm. This adaptation prevents reflections and thus allows operation at higher bit rates. For the sake of simplicity, the state 403 (sic) or sic state 403 is always referred to below.FIG. 10 shows the subscriber station 10 in more detail, which has the communication control device 11 and the transmitting / receiving device 12, as already described above with reference to FIG. 1. In the transmitting mode of the subscriber station 10, the transmitting / receiving device 12 outputs at its output differential voltages U_H=2.9 V and U_L=0.9 V for the signals CAN_H, CAN_L, as described above with reference to FIG. 7. The transmitting / receiving device 12 can have an event detection module 125 for detecting one of the events E 1, E 2, E 3 shown in FIGS. 2 and 9. Event detection module 125 may in particular have a counter for evaluating received signal RxD and / or a timer for detecting whether a predetermined time has elapsed. subscriber station 30 may be designed in the same way as subscriber station 10.According to FIG. 10, the subscriber station 10 has an electrical circuit with a bus voltage supply module 13, a bus voltage detection module 14, a bus voltage holding module 15, a bus voltage setting module 16, a bus voltage driver 17 and a bus bias module 18. The first connection network 123, which may comprise at least two resistors, not designated in more detail in FIG. 10, serves for connecting the detection module 14 to the connections for the signals CAN_H, CAN_L. The second connection network 124, which may have at least four resistors, which are not designated in more detail in FIG. 10, serves for connecting the transmitting / receiving device 12 to the connections for the signals CAN_H, CAN_L. The voltage supply 130 supplies the subscriber station 10 with an electrical voltage of 3.3 V.The bus voltage supply module 13 is connected at one side to the electric voltage supply 130. On the other hand, the bus voltage supply module 13 is connected to ground, in particular CAN-GND. In the present exemplary embodiment, the bus voltage supply module 13 is designed as a voltage divider having six resistors 131 to 136. The resistors 131 to 136 constitute reference voltage sources as follows. A first resistor 131 is connected in series with a second resistor 132. The second resistor 132 is connected to ground, in particular CAN-GND. A voltage or potential of U1=2.1 V is established between the resistors 131, 132 during operation of the subscriber station 10. A third resistor 133 is connected in series with a fourth resistor 134. The fourth resistor 134 is connected to ground, in particular CAN-GND. A voltage or potential of U3=2.5 V is established between the resistors 133, 134 during operation of the subscriber station 10. A fifth resistor 135 is connected in series with a sixth resistor 136. The sixth resistor 136 is connected to ground, in particular CAN-GND. A voltage or potential of U2=1.9 V is established between the resistors 135, 136 during operation of the subscriber station 10.The resistors 131 to 136 thus provide reference voltages U1, U2, U3 for the subscriber station 10. Voltages U2, U3 are usable as different bus biases for bus 40. If desired, module 130 is configured to provide more than two different bus biases to bus 40, particularly using more than six resistors 131-136.A first end of a first electrical line L 1 is connected to a connection of the resistors 131, 132, said first electrical line being connected at its other end to the bus voltage holding module 15. A second electrical line L2 is connected to a connection of the resistors 135, 136, the second electrical line being connected at its other end to the bus voltage setting module 16. A third electrical line L3 is connected to a connection of the resistors 133, 134, the third electrical line being connected at its other end to the bus voltage setting module 16.At least one input of the bus voltage detection module 14 is connected to the terminals for the bus signals CAN_H, CAN_L on the bus 40. An output of the bus voltage detection module 14 is connected to a first input of the bus voltage holding module 15. The first electric line L1 is connected at its other end, which is not connected to the connection of the resistors 131, 132, to an input of the bus voltage holding module 15. The bus voltage sensing module 14 has a control block 141 configured to switch a switch 142, and at least one storage element 143. The control block 141 is configured to control the switching position of the switch 142. The control block 141 may also be referred to as a sensing module control block. The storage element 143 is embodied as at least one capacitor 143 in the example of FIG. 5.The storage element 143 is used to store the current bus potential. When the storage element 143 is charged, the control block 141 controls the switch 142 to open the switch 142. The bus potential is thus constantly present at the first input of the bus voltage holding module 15. As a result, the bus voltage holding module 15 remains in the state given by the difference of threshold voltage U1, which is 2.1 V here, and bus potential on the bus 40.The bus voltage holding module 15 is designed as an operational amplifier.The output of the bus voltage holding module 15 is connected to an input of the bus voltage setting module 16. In addition, the lines L 2, L 3 are each connected to an input of the bus voltage setting module 16.The bus voltage setting module 16 has a control block 161 configured to switch a switch 162. The control block 161 is configured to control the switching position of the switch 162. The control block 161 may also be referred to as a setting module control block. The switch 162 is a changeover switch in the example of FIG. 5.An output of the bus voltage adjustment module 16, which is connected to one end of the switch 162, is connected to a first input of the bus voltage driver 17. The output of the bus voltage driver 17 is connected to a second input of the bus voltage driver 17. The output of the bus voltage driver 17 is thus fed back to the input of the driver 17.The bus bias module 18 is connected between the bus voltage driver 17 and the terminals for the bus signals CAN_H, CAN_L on the bus 40. Thus, the bus bias module 18 is also electrically connected to the terminals for the bus signals CAN_H, CAN_L. The bus bias module 18 has a control block 181 configured to control the switching position of a switch 182. The control block 181 switches the switch 182. The control block 181 may also be referred to as a bus bias module control block.Depending on the control of the control block 161, the switch 162 switches either the voltage U2= 1.9 V from the line L2 or the voltage U3=2.5 V from the line L3 as a reference to the bus voltage driver 17. the bus voltage driver 17 drives the bus bias voltage for the signals CAN_L and CAN_H via the connections for the bus wires 41, 42 to the bus 40, respectively, when the switch 182 is closed.For the operation of the subscriber station 10 in the bus system 1, the modules 13 to 18 are designed as follows in order to set a recessive bus potential with mixed operation or to set a recessive bus potential without mixed operation.The recessive bus potential may also be referred to as a bus bias for bus 40. This bus bias voltage constitutes the bus center voltage Vcm which is equal to the regenerative bus potential.The subscriber station 10 passes through the following time(s) sequence(s) in order to set a regenerative bus potential with mixed operation.After starting, the subscriber station 10 goes to a voltage U3=2.5 V if the subscriber station 10 cannot yet exclude that there is a subscriber station on the bus 40 which uses a voltage of 5 V as bus voltage supply.The subscriber station 10, as well as the subscriber station 30, is configured to "release" the bus center voltage Vcm=U3=2.5 V at a predetermined point in time and to detect or measure only with the detection module 14 to which voltage the bus 40 is set.The release and detection take place for a predetermined period of time T_M 1 (FIG. 2 ), in particular a predetermined number of bits. Such a predetermined time t1 is, for example, during the EOF (End of Frame) having 7 recessive bits, as shown in FIG. 2 and mentioned above. In particular, the time is after a predetermined bit of the 7 recessive bits.Thus, all subscriber stations that use a bus voltage supply of 3 V, i.e., the subscriber stations 10, 30 here, release the bus center voltage Vcm=U3=2.5 V for a predetermined time duration T_M 1 (FIG. 2 ), in particular at the end of a frame 450 in EOF (FIG. 2 ). For this purpose, the control block 181 controls the switch 182 of the bus bias module 18 such that the switch 182 interrupts the connection to the bus 40 for the predetermined time duration T_M 1 (FIG. 2 ). The subscriber station disconnects the bus bias for bus 40.First Case: Heterogeneous Bus System 1According to a first case, which corresponds to the present exemplary embodiment, a heterogeneous bus system 1 is present in which at least one subscriber station, for example the subscriber station 20, uses a voltage supply 130 of 5 V and accordingly awaits and feeds a bus mid-point voltage Vcm=U3=approximately 2.5 V.However, after starting, the subscriber station 10 does not yet know whether a heterogeneous bus system 1 is present or whether a homogeneous bus system 1 is present in which all subscriber stations 10, 20, 30 on the bus 40 use the same bus voltage supply as the subscriber station 10, in particular 3.3 V, so that the bus center voltage Vcm=U2=approximately 1.9 V is fed as bus bias voltage to the bus 40.Transmission Mode of Subscriber Station 10At the next arbitration phase 451 on the bus 40, the subscriber station 10 starts for the review state 402, which is predetermined according to a value of the transmit signal TxD=H (high=high), with a bus voltage of 2.5 V. That is, the control block 161 has put the switch 162 in connection with the line L 3. Consequently, the bus center voltage Vcm=U3=about 2.5 V is supplied as a bus bias voltage to the bus 40.If the subscriber station 10 wins the arbitration, then the subscriber station 10 is also allowed to transmit to the bus 40 in the subsequent data phase 452. For this purpose, after the arbitration phase 451 and before the data phase 452, the subscriber station 10 pulls the bus level for the review state 402 to its desired voltage, namely U2=1.9 V, in the next coming review state 402 and sends it. In this case, the bus center voltage Vcm=U2=approximately 1.9 V is thus set and is fed as a bus bias voltage to the bus 40.After completion of data phase 452, end 459 of frame 450, including the EOF, follows, as shown in FIG. 2. The transition from U3 to U2 takes place "soft". Consequently, the voltage smoothly transitions to the new value because the inherent impedance of the bus 40 with the connected subscriber stations 10, 20, 30 and the lines between the subscriber stations 10, 20, 30 has a attenuating effect on the voltage change.The subscriber station 10, in particular its transmitting / receiving device 12 and / or at least one of its control blocks 141, 161, 181, reliably recognizes the EOF by evaluating the signal RxD (FIG. 6 ) since the following applies for more than 5 bits: RxD=H (high=high). EOF is 7 bits long. For this purpose, the transmitting / receiving device 12 and / or at least one of its control blocks 141, 161, 181 can have the event detection module 125, in particular a counter, for evaluating the received signal RxD.At a certain, in particular late, time, for example at bit 6, in the EOF, the subscriber station 10 determines whether a Vcm >1.9 V is present on the bus 40. Specifically, the threshold is Vcm=1.9 V+ 10%.If, for example, the subscriber station 20 uses a bus voltage supply of 5 V and accordingly feeds in a bus mid-voltage Vcm=U3=2.5 V, the measurement of the detection module 14 results in the storage element 142 having been charged to a voltage of, for example, 2.5 V. Consequently, the bus center voltage Vcm=U3=2.5 V is then present at the first input of the bus voltage holding module 15.Thus, subscriber station 10 evaluates that there are 5V subscriber stations on bus 40. Thus, the control block 161 controls the switch 162 to switch the potential U3=2.5 V of the line L3 to the input of the module 17. Consequently, the center bus voltage Vcm=U3=about 2.5 V can be applied as a bus bias to the bus 40 via the switch 182.The setting to the bus bias voltage on the bus 40 or the potential U3=2.5 V can take place in particular during bit 7 or one of the following 4 recessive bits.Subscriber station 10 does not transmit receive modeIf the subscriber station 10 does not transmit, the subscriber station 10 either loses arbitration or has no data or message 45 to transmit. Thus, the subscriber station 10 receives only the signals CAN_H, CAN_L from bus 40 and generates the RxD signal therefrom.The subscriber station 10, in particular its transmitting / receiving device 12 and / or at least one of its control blocks 141, 161, 181, reliably recognizes the EOF by evaluating the signal RxD, since RxD=H (high=high) applies to more than 5 bits. EOF is 7 bits long. For this purpose, the transmitting / receiving device 12 and / or at least one of its control blocks 141, 161, 181 can have the event detection module 125, in particular a counter, for evaluating the received signal RxD.At a predetermined, in particular late, time, for example at bit 6, in the EOF, the subscriber station 10 determines whether a Vcm >1.9 V is present on the bus 40. Specifically, the threshold is Vcm=1.9 V+ 10%.If, for example, the subscriber station 20 uses a bus voltage supply of 5 V and accordingly feeds in a bus mid-voltage Vcm=U3=2.5 V, the measurement of the detection module 14 results in the storage element 142 having been charged to a voltage of, for example, 2.5 V. Consequently, the bus center voltage Vcm=U3=2.5 V is then present at the first input of the bus voltage holding module 15.Thus, subscriber station 10 evaluates that there are 5V subscriber stations on bus 40. As a result, the control block 161 controls the switch 162 to switch the potential U3=2.5V of the line L3 to the input of the module 17. The setting to the potential U3=2.5 V can take place in particular during bit 7 of the EOF (FIG. 1 ) or one of the following 4 recessive bits. A bus voltage of 2.5 V is thus predefined for the recessive state 402, which is predefined according to a value of the transmission signal TxD=H (high=high). That is, the control block 161 has placed the switch 162 in connection with the line L3.Second case: Homogeneous bus system 1According to a second case, a homogeneous bus system 1 is present in which all subscriber stations, i.e. also the subscriber station 20, use a 3.3 V bus voltage supply 130.However, after starting, the subscriber station 10 does not yet know whether a heterogeneous bus system 1 is present or whether a homogeneous bus system 1 is present in which all subscriber stations on the bus 40 use the same bus voltage supply as the subscriber station 10, in particular 3.3 V, so that a bus center voltage Vcm=U2=approximately 1.9 V is fed to the bus 40.One of the subscriber stations 10, 20, 30 sends a frame 450 on the bus 40. In the next arbitration phase 451 on the bus 40, the sending subscriber stations 10, 20, 30 start for the review state 402, which is predefined according to a value of the transmit signal TxD=H (high=high), with a bus voltage of 2.5 V. That is, the control block 161 has placed the switch 162 in the connection to the line L 3. The subscriber station(s) who do not wish to send data expect / n that one of the other subscriber stations also uses a 5 V bus voltage supply.In the next step, each of the subscriber stations 10, 20, 30 proceeds according to one of the previously described sequences for transmitting operation or receiving operation in order to determine whether one of the other subscriber stations uses a bus voltage supply of 5 V.In a homogeneous bus system 1, the detection with the bus voltage detection device 14 reveals that none of the other subscriber stations uses a bus voltage supply of 5 V.Therefore, the subscriber stations 10, 20, 30 of the bus system 1 permanently set the switch 162 in such a way that the potential of the line L2 is connected to the input of the module 17. "Permanent" means that no detections are carried out with the detection module 14 after the described setting of the module 16. Alternatively, however, "permanent" can mean that after the described setting of the module 16 from time to time, in particular each Nth frame 450, a measurement is carried out using the module 14. N is a natural number greater than 1. the time intervals between the measurements need not be the same.The subscriber station 10 is thus configured to carry out a detection or measurement during at least one recessive bus status in order to determine whether a bus center voltage Vcm >1.9 V is present on the bus 40. Specifically, the threshold is 1.9 V + 10%.Optionally, at least one of the subscriber stations 10, 30 could additionally detect at at least one dominant level 402 of the borrow of the arbitration during the arbitration phase 451 whether the borrow of the arbitration uses a bus voltage supply of 5V or 3V. Thus, in the arbitration phase 451, the subscriber stations 10, 30 would additionally carry out a detection with the detection module 14 starting from a time t2 (FIG. 2 ) for a time duration T_M2 (FIG. 2 ) in order to determine whether a bus center voltage Vcm >1.9 V is present on the bus 40. Specifically, the threshold is 1.9V+ 10%. The time periods T_M1, T_M2 may be the same or different.Optionally, at least one of the subscriber stations 10, 30 could additionally perform detection with the detection module 14 during the SIC phase that is equal to the arbitration phase 451. For this purpose, the value of Vcm_sic is determined within the time duration t_sic<= 355ns (FIG. 9 ). The time duration t_sic corresponds to the minimum time during which the state 403 (sic) is active, starting from the transition from the state 401 (dom) to the state 402 (rec) at the end of the arbitration. The time duration T_M 1 may be different from the time of t_sic.The aforementioned methods are also applicable if at least one of the subscriber stations 10, 30 functions as a CAN-XL node, i.e. sends a CAN-XL message 45.According to the embodiments described above, the transmitting / receiving device 12 of the subscriber station 10 described is configured to become lower-ohmic in a controlled manner than the other transmitting / receiving devices 20, 30 on the bus 40. As soon as the "low impedance becomes" has taken place, the subscriber station 10, in particular its transmitting / receiving device 12, can transmit its message 45 or 47 within the limits of the EMC specification. Following the transmission process, the subscriber stations 10 must have the same high impedance as the other subscriber stations 20, 30 on the bus 40, with the result that the bus voltage is then set elsewhere in the middle. For this process, the subscriber station 10 again has a little time, which is defined in the CAN specification.FIG. 11 shows a subscriber station 100 according to a second exemplary embodiment.The subscriber station 100 is largely designed in the same way as the subscriber station 10 of the preceding exemplary embodiment. Therefore, only the differences from the subscriber station 10 of the preceding embodiment will be described below.In contrast to the subscriber station 10 of the preceding exemplary embodiment, the subscriber station 100 of FIG. 11 has at least one storage element 19. The storage element 19 serves to store the voltage U5 at the output of the holding module 15.This makes it possible to ensure even better that the bus potential is present at the corresponding input of module 16, which was detected by module 14.As a result, the function of at least the module 15 and thus the result of the module 16 is further improved in comparison with the subscriber station 10 of the preceding exemplary embodiment. As a result, the function of the subscriber station 100 is also further improved in comparison with the subscriber station 10 of the preceding exemplary embodiment.FIG. 12 shows a subscriber station 101 according to a third exemplary embodiment.The subscriber station 101 is largely designed in the same way as the subscriber station 10 of the preceding exemplary embodiment. Therefore, only the differences from the subscriber station 10 of the preceding embodiment will be described below.In contrast to the subscriber station 10 of the preceding exemplary embodiment, the subscriber station 101 of FIG. 12 does not have a module 17.This further simplifies the circuit of the subscriber station 10.According to a fourth exemplary embodiment, the module 13 is designed as a semiconductor which has three band gap derivatives (band gap derivatives).That is, as shown in FIGS. 10 to 12, the module 13 has a first band gap derivative 131, 132 which provides the voltage U1 for the line L1 of the subscriber stations 10, 100, 101. In addition, the module 13 has a second band gap derivative 133, 134, which provides the voltage U3 for the line L3 of the subscriber stations 10, 100, 101. In addition, the module 13 has a third band gap derivative 135, 136, which provides the voltage U 2 for the line L 2 of the subscriber stations 10, 100, 101. Thereby, instead of the resistors 131 to 136 in FIGS. 10 to 12, the band gap derivatives (bandgap derivatives) of the semiconductor provide the reference voltages U 1, U 2, U 3 described above.Incidentally, the function is the same as described in the foregoing embodimentsAll previously described embodiments of the transmitting / receiving devices 12, 22, the subscriber stations 10, 20, 30, the bus system 1 and the method according to the exemplary embodiment embodied therein and the modifications thereof can be used individually or in all possible combinations. In addition, the following modifications are in particular conceivable.The bus system 1 described above is described on the basis of a bus system based on the CAN protocol. However, the bus system 1 according to the exemplary embodiment can alternatively be another type of communication network in which the signals are transmitted as differential signals.It is advantageous, but not necessarily, prerequisite that in the bus system 1 an exclusive, collision-free access of a subscriber station 10, 20, 30 to the bus 40 is ensured at least for specific periods of time.Bus system 1 according to the exemplary embodiment and its modifications is, in particular, a bus system in which communication can be carried out between at least two of subscriber stations 10, 20, 30 according to two different CAN standards, such as, for example, CAN-HS or CAN FD or CAN SIC or CAN XL. The functionality of the exemplary embodiment described above can thus be used, for example, in transmitting / receiving devices 12, 22 which are to be operated in such a bus system.The number and arrangement of the subscriber stations 10, 20, 30 in the bus system 1 according to the exemplary embodiment and its modifications can be selected as desired.It is possible in particular for the subscriber station 10 to have a bus voltage supply of 5 V and for the subscriber station to have a bus voltage supply of 3.3 V.In addition, the bus voltage supply of one of the subscriber stations 10, 20, 30 is not limited to 3.3 V. The bus voltage supply may have a value other than 3.3 V. The above-described principle of bus system 1 with subscriber stations 10, 20, 30 in mixed operation can also be used for this purpose. If necessary, the voltages of the module 13 are to be adapted accordingly for this purpose.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureISO11898-1:2015 [0002, 0074, 0075]

Claims

Subscriber station (10; 30) of a serial bus system (1), having a transmitting / receiving device (12) for transmitting a digital transmission signal (TxD) as an analog differential signal (CAN_H, CAN_L) onto a bus (40) of the bus system (1) in order to transmit a message (45; 46; 47) to at least one other subscriber station (10; 20; 30) of the bus system (1), and / or for receiving an analog signal (CAN_H, CAN_L; VDIFF) from the bus (40), a switching module (18) for switching off a bus bias voltage (U2; U3) for the bus (40) during a predetermined detection time period (T_M1; T_M1, T_M2; T_M3), a bus voltage detection module (14) for detecting the bus voltage (Vcm) received by the transmitting / receiving device (12) from the bus (40) during the predetermined detection time period (T_M1; T_M1, T_M2; T_M3), and a bus voltage setting module (16) for setting the bus bias voltage (U2; U3) to a voltage value resulting from detection performed by the bus voltage detection module (14) during the predetermined detection time period (T_M1; T_M1, T_M2; T_M3).Subscriber station (10; 30) according to claim 1, further comprising a detection module control block (141) for controlling the bus voltage detection module (14) such that during the predetermined detection time period (T_M1; T_M1, T_M2) on the bus (40) there is a recessive state (402) rewritable from a dominant state (401) on the bus (40).Subscriber station (10; 30) according to claim 1 or 2, further comprising a detection module control block (141) for controlling the bus voltage detection module (14) such that during the predetermined detection time period (T_M1; T_M1, T_M2) on the bus (40) a transition from a dominant state (401) to a recessive state takes place, which is rewritable from a dominant state (401) on the bus (40), wherein the transition from the dominant state (401) to a recessive state is in particular an SIC state (403).Subscriber station (10; 30) according to one of the preceding claims, further comprising a detection module control block (141) for controlling the bus voltage detection module (14) such that during the predetermined detection time period (T_M1; T_M1, T_M2) the end of the arbitration phase (451) takes place and a dominant state prevails on the bus (40).Subscriber station (10; 30) according to one of the preceding claims, wherein the bus voltage detection module (14) also comprises a switch (142) and a storage element (143), and wherein the detection module control block (141) is configured to control the switch (142) for connecting the storage element (143) to the bus (40) in order to detect the bus voltage (Vcm) received by the transmitting / receiving device (12) from the bus (40).Subscriber station (10; 30) according to one of the preceding claims, further comprising a bus voltage provision module (13) for providing two different bus biases (U2; U3), wherein the bus voltage setting module (16) is configured to set one of the two different bus biases (U2; U3) for the transmitting / receiving device (12) on the basis of the bus voltage (Vcm) detected by the bus voltage detection module (14) during the predetermined detection time period (T_M1; T_M1, T_M2).The subscriber station (10; 30) of claim 6, wherein the bus voltage providing module (13) comprises a voltage divider with six resistors (131...136) for providing the two different bus biases (U2; U3).The subscriber station (10; 30) of claim 6, wherein the bus voltage providing module (13) comprises a semiconductor having three band gap derivatives (131, 132; 133, 134; 135, 136) for providing the two different bus bias voltages (U2; U3).The subscriber station (10; 30) according to any of the preceding claims, wherein the bus voltage adjustment module (16) comprises a changeover switch (162) and an adjustment module control block (161) for controlling the position of the changeover switch (162) on the basis of the bus voltage (Vcm) detected by the bus voltage detection module (14) during the predetermined detection time period (T_M1; T_M1, T_M2).Subscriber station (10; 30) according to one of the preceding claims, wherein the subscriber station (10; 30) is configured to negotiate with the other subscriber stations (10; 20; 30) of the bus system (1) which of the subscriber stations (10; 20; 30) has exclusive access to the bus (40) in the following second communication phase (452) and is thus allowed to send their message (45; 46; 47) during a first communication phase (451).Subscriber station (10; 30) according to one of the preceding claims, wherein the transmitting / receiving device (12) is configured to generate the analog differential signal (CAN_H, CAN_L) in a first communication phase (451) of the message (45) with a different physical layer (451_P) than in a second communication phase (452).Subscriber station (10; 30) according to one of the preceding claims, further comprising an event detection module (125) for detecting an event (E1; E2; E3), after which the bus voltage detection module (14) is to carry out a detection of the bus voltage (Vcm) present on the bus (40), wherein the detection module control block (141) is configured to control the bus voltage detection module (14) for detecting the bus voltage (Vcm) present on the bus (40) during the predetermined detection time period (T_M1; T_M1, T_M2; T_M3) after the event detection module (125) has detected the event (E1; E2; E3).The subscriber station (10; 30) of claim 12, wherein the event (E1) is a predetermined number of directly consecutive re-intensive bits at the end (EOF) of a frame (450) sent over the bus (40) for the message (45; 46; 47).Subscriber station (10; 30) according to claim 12 or 13 and when dependent on claim 10, wherein the event (E2) is that at the end of the first communication phase (451) the subscriber station (10; 20; 30) is determined which has the exclusive access to the bus (40) in the following second communication phase (452) and is thus allowed to send its message (45; 46; 47).Subscriber station (10; 30) according to one of the preceding claims, further comprising a bus voltage holding module (15) for holding the bus voltage (Vcm) detected by the bus voltage detection module (14) on the bus (40), and optionally further comprising a storage element (19) arranged between the bus voltage holding module (15) and the bus voltage setting module (16) for storing a voltage (U5) at the output of the bus voltage detection module (14).Subscriber station (10; 30) according to one of the preceding claims, further comprising a bus voltage driver (17) for driving the bus bias voltage (U2; U3) for the transmitting / receiving device (12) set by the bus voltage setting module (16) onto the bus (40).Subscriber station (20) for a serial bus system (1), additionally having a communication control device (11) for controlling the communication in the bus system (1) and for generating the transmission signal (TXD), wherein the subscriber station (20) is designed for the communication in a bus system (1) in which exclusive, collision-free access of a subscriber station (10, 20, 30) to the bus (40) of the bus system (1) is ensured at least temporarily.Bus system (1), having a bus (40), and at least two subscriber stations (10, 20; 10, 30; 20, 30) which are connected to one another via the bus (40) in such a way that they can communicate with one another in series, and of which at least one subscriber station (10, 20; 10, 30; 20, 30) is a subscriber station (10; 30) according to one of the preceding claims.Method for communication with differential signals (CAN_H, CAN_L) in a serial bus system (1), in which a subscriber station (10:30) of the bus system (1) has a transmitting / receiving device (12) for transmitting a digital transmission signal (TxD) as an analog differential signal (CAN_H, CAN_L) onto a bus (40) of the bus system (1) in order to transmit a message (45; 46; 47) to at least one other subscriber station (10; 20; 30) of the bus system (1), and / or for receiving an analog signal (CAN_H, CAN_L; VDIFF) from the bus (40), wherein the method has the steps of switching off, with a switching module (18), a bus bias voltage (U2; U3) for the bus (40) during a predetermined detection time period (T_M1; T_M1, T_M2; T_M3), detecting, with a bus voltage detection module (14), the bus voltage (Vcm) received from the bus (40) by the transmitting / receiving device (12) during the predetermined detection time period (T_M1; T_M1, T_M2; T_M3), and setting, with a bus voltage setting module (16), the bus bias voltage (U2; U3) to a voltage value derived from a voltage value derived from a voltage value derived from the bus voltage detection module (14) during the predetermined detection time period (T_M1; T_M1, T_M2; T_M3).

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