PARTICIPANT STATION FOR A SERIAL BUS SYSTEM AND METHOD FOR COMMUNICATION IN A SERIAL BUS SYSTEM

Description

Technical area

[0001] The present invention relates to a subscriber station for a serial bus system and a method for communication in a serial bus system that operates with a high data rate as well as great flexibility and high error robustness. State of the art

[0002] Bus systems for communication between sensors and control units, for example in vehicles, are designed to enable the transmission of large amounts of data, depending on the number of functions of a technical system or vehicle. This often requires data to be transmitted faster from sender to receiver than before, and large data packets to be able to be transmitted if necessary.

[0003] A bus system is currently being introduced in vehicles. It transmits data as messages in the ISO 11898-1:2015 CAN protocol specification using CAN FD. The messages are transmitted between the bus system's participants, such as sensors, control units, encoders, etc. CAN FD is initially being deployed by most manufacturers in the vehicle with a 2 Mbit / s data bit rate and a 500 kbit / s arbitration bit rate.

[0004] To enable even higher data rates, a successor bus system to CAN FD, referred to as CAN XL, is currently being developed. In addition to pure data transport via the CAN bus, CAN XL is intended to support other functions, such as functional safety, data security, and quality of service (QoS). These are fundamental features required in an autonomous vehicle.

[0005] DE 10 2012 200 997 A1 discloses a method and device for testing the correct functioning of a serial data transmission in a bus system with at least two bus nodes. In a bus node (transmitting node), which is the transmitter of a frame in a transmit signal on the bus, the correct functioning of the data transmission is tested during transmission by comparing a transmit signal sent to the bus connection unit with the receive signal received by the bus connection unit. To perform this comparison, the transmitting bus node determines a time delay between the transmit signal sent by the bus connection unit and the receive signal received by the bus connection unit in order to generate a transmit signal delayed by the time delay for the comparison to be performed.

[0006] When transmitting data in a frame over a channel (CAN bus), corruption can always occur, particularly due to external influences, especially radiation. One of the tasks of the CAN XL communication protocol is to detect and discard corrupted frames. The quality of error detection can be expressed by the residual error probability. The residual error probability indicates the probability that a frame will be accepted as correct despite an error at a receiving station (receiving node) in the bus system that is not a sender of the frame.

[0007] For the functional safety of a system, it is very advantageous and important that the residual error probability is as low as possible. Class 1 errors, namely erroneously inverted bits (bit flips), and / or class 2 errors, namely locally accumulated bit errors (burst errors), can be detected using a checksum (CRC = Cyclic Redundancy Check) transmitted within the frame.

[0008] However, it is problematic if edges are generated or shifted due to external interference. This can lead to the receiving station (receiving node) of the bus system, which is not a frame sender, performing a shifted sampling of the bit stream in the received frame. The sampling of the bit stream can be shifted by one or more bits, which is also referred to as a Class 3 error. In such errors, the receiving station is unable to reliably detect the error using the checksum (CRC). Disclosure of the invention

[0009] Therefore, the object of the present invention is to provide a subscriber station for a serial bus system and a method for communication in a serial bus system that solve the aforementioned problems. In particular, a subscriber station for a serial bus system and a method for communication in a serial bus system are to be provided in which errors due to additional or shifted edges in a bit stream are detected with high reliability, in order to achieve high error robustness of the communication even at high data rates and an increase in the amount of payload data per frame.

[0010] The problem is solved by a subscriber station for a serial bus system having the features of claim 1.The subscriber station has a communication control device for controlling communication between the subscriber station and at least one other subscriber station of the bus system, and a transmitting / receiving device for transmitting a transmit signal generated by the communication control device to a bus of the bus system, such that, for a message exchanged between subscriber stations of the bus system, the bit time of a signal transmitted onto the bus in the first communication phase can differ from a bit time of a signal transmitted in the second communication phase, wherein the communication control device is configured to generate the transmit signal according to a frame and to insert at least one field into the frame which is configured to check whether the bit stream of the frame in a subscriber station of the bus system that receives the frame is offset by at least one bit compared to the expected frame, as described in claim 1.

[0011] By designing the subscriber station, the residual error probability for a frame received from the bus can be reduced. This allows a receiver of the frame to decode the correct frame length and therefore also check the checksum (CRC = Cyclic Redundancy Check) at the correct location at the end of the frame. This allows communication errors in the bus system to be detected quickly and reliably.

[0012] The subscriber station can guarantee the detection of a data stream offset of up to N bits. This enables secure transmission of frames over the bus, even in the presence of interference.

[0013] Another advantage is that the measures to reduce the residual error probability with respect to Class 3 errors require only a very small number of additional control bits. The new FCP field is cleverly integrated into the frame. As a result, the data overhead in addition to the actual payload data is very low.

[0014] If each fixed stuff bit is replaced by an FCP field, the data overhead can even be zero. Furthermore, the format check is very rigorous, as several fixed stuff bits, and thus FCP fields, are replaced. Because the data overhead is minimal or not increased, the net transmittable data rate can be optimized, so that communication in the bus system is not slowed down more than necessary.

[0015] As a result, even if the amount of user data per frame increases, the subscriber station can ensure that frames are sent and received with high functional reliability, with high flexibility with regard to current events in the operation of the bus system and with a low error rate.

[0016] In particular, the subscriber station in the bus system makes it possible to maintain an arbitration known from CAN in an initial communication phase and yet significantly increase the transmission rate compared to CAN or CAN FD.

[0017] The procedure performed by the subscriber station can also be used if the bus system also includes at least one CAN subscriber station and / or at least one CAN FD subscriber station that sends messages according to the CAN protocol and / or CAN FD protocol.

[0018] Advantageous further embodiments of the subscriber station are specified in the dependent claims.

[0019] According to one embodiment, the communication control device is configured to insert the at least one field after a data field in the frame. The communication control device can be configured to insert the at least one field in the frame after a frame checksum that was formed across all bits in the frame.

[0020] According to another embodiment, the communication control device is designed to insert the at least one field before a data field in which payload data of the frame is inserted.

[0021] For a particularly high net data rate, the communication control device is designed to design and / or arrange the at least one field in such a way that the content of the at least one field is to be used in a receiving subscriber station not only for the function of checking the offset of the bit stream, but also for a different function.

[0022] According to yet another embodiment, the communication control device is designed to insert one of said fields into the frame always after a fixed number of bits.

[0023] It is conceivable that the communication control device is configured to insert the at least one field as a fixed stuff bit in the frame, wherein the communication control device is configured to insert all fixed stuff bits into the frame according to a fixed bit stuffing rule, according to which a fixed stuff bit is to be inserted after a fixed number of bits. In this case, the communication control device may be configured to select the value of the field depending on which value should be selected for the stuff bit, so that an inverse stuff bit is inserted in the frame after five identical bits in a row.

[0024] Optionally, the communication control device is designed to use the same value for all of the aforementioned fields in the frame.

[0025] In a specific embodiment, the communication control device is designed to use an even number of M bits for the at least one field, wherein the first half of the M bits each have the same first value, and wherein the second half of the M bits each have the same second value, which is inverse to the first value.

[0026] In another specific embodiment, the communication control device is designed to insert at least the least significant bits of the number of fixed stuff bits inserted in frames into the at least one field.

[0027] In yet another specific embodiment, the communication control device is configured to insert into the at least one field at least the least significant bits of the number of frames that have already been sent onto the bus by the communication control device.

[0028] It is conceivable that the communication control device is designed to provide a bit after switching from the second communication phase to the first communication phase, during which bit the transmitting / receiving device has time to switch to the second communication phase, wherein the communication control device is designed, in the case in which the subscriber station of the bus system receives the frame but is not a transmitter of the frame, to use the bit to check whether the bit stream of the received frame is offset by at least one bit compared to the expected frame.

[0029] It is possible that the frame created for the message is constructed in a way that is compatible with CAN FD, whereby in the first communication phase it is negotiated which of the participant stations of the bus system will receive at least temporarily exclusive, collision-free access to the bus in the subsequent second communication phase.

[0030] The previously described subscriber station can be part of a bus system that also comprises a bus and at least two subscriber stations connected to each other via the bus in such a way that they can communicate with each other serially. At least one of the at least two subscriber stations is a previously described subscriber station.

[0031] The aforementioned object is also achieved by a method for communication in a serial bus system according to claim 15. The method is carried out with a subscriber station of the bus system, which has a communication control device and a transmitting / receiving device, wherein the method comprises the steps of controlling, with the communication control device, communication of the subscriber station with at least one other subscriber station of the bus system, and transmitting, with the transmitting / receiving device, a transmission signal generated by the communication control device to a bus of the bus system, so that for a message exchanged between subscriber stations of the bus system, the bit time of a signal transmitted on the bus in the first communication phase can differ from a bit time of a signal transmitted in the second communication phase,wherein the communication control device generates the transmission signal according to a frame and inserts into the frame at least one field designed to check whether the bit stream of the frame in a subscriber station of the bus system receiving the frame is offset by at least one bit compared to the expected frame, as described in claim 15.

[0032] The method offers the same advantages as previously mentioned with regard to the subscriber station.

[0033] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. 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. Drawings

[0034] The invention is described in more detail below with reference to the accompanying drawings and exemplary embodiments. They show: Fig. 1 a simplified block diagram of a bus system according to a first embodiment; Fig. 2 a diagram illustrating the structure of a message that can be sent by a subscriber station of the bus system according to the first embodiment; Fig. 3 a simplified schematic block diagram of a subscriber station of the bus system according to the first embodiment; Fig. 4 a time course of bus signals CAN-XL_H and CAN-XL_L at the subscriber station according to the first embodiment; Fig. 5 a time profile of a differential voltage VDIFF of the bus signals CAN-XL_H and CAN-XL_L at the subscriber station according to the first embodiment; Fig. 6a diagram illustrating the structure of a message that can be sent by a subscriber station of the bus system according to a second embodiment; and Fig. 7 a diagram illustrating the structure of a message that can be sent by a subscriber station of the bus system according to a third embodiment.

[0035] In the figures, identical or functionally equivalent elements are provided with the same reference numerals unless otherwise indicated. Description of the embodiments

[0036] Fig. 1 shows, as an example, a bus system 1, which is fundamentally designed, in particular, for a CAN bus system, a CAN FD bus system, a CAN XL 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.

[0037] In Fig. 1 The bus system 1 has a plurality of subscriber stations 10, 20, 30, each of which is connected to a bus 40 with a first bus wire 41 and a second bus wire 42. The bus wires 41, 42 can also be called CAN_H and CAN_L or CAN-XL_H and CAN-XL_L and are used for electrical signal transmission after coupling in the dominant levels or generating recessive levels or other levels for a signal in the transmit state. Messages 45, 46 in the form of signals can be serially transmitted between the individual subscriber stations 10, 20, 30 via the bus 40. If an error occurs during communication on the bus 40, as indicated by the jagged black block arrow in Fig. 1 As shown, an error frame 47 (error flag) can optionally be sent. Participant stations 10, 20, 30 are, for example, control units, sensors, display devices, etc. of a motor vehicle.

[0038] As in Fig. 1As shown, the subscriber station 10 has a communication control device 11, a transmitting / receiving device 12 and a format checking module 15. The subscriber station 20 has a communication control device 21 and a transmitting / receiving device 22. The subscriber station 30 has a communication control device 31, a transmitting / receiving device 32 and a format checking module 35. The transmitting / receiving devices 12, 22, 32 of the subscriber stations 10, 20, 30 are each directly connected to the bus 40, even if this is not shown in Fig. 1 is not illustrated.

[0039] The communication control devices 11, 21, 31 each serve to control 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 that are connected to the bus 40.

[0040] The communication control devices 11, 31 create and read first messages 45, which are, for example, modified CAN messages 45. The modified CAN messages 45 are constructed on the basis of a CAN XL format, which with respect to Fig. 2 is described in more detail, and in which the respective format check module 15, 35 is used. The communication control devices 11, 31 can also be designed to provide a CAN XL message 45 or a CAN FD message 46 for the transmitting / receiving device 32 or to receive one from it, as required. The respective format check modules 15, 35 are also used here. The communication control devices 11, 31 thus create and read a first message 45 or a second message 46, wherein the first and second messages 45, 46 differ in their data transmission standard, namely CAN XL or CAN FD in this case.

[0041] The communication control device 21 can be designed like a conventional CAN controller according to ISO 11898-1:2015, i.e., like a CAN FD-tolerant Classical CAN controller or a CAN FD controller. The communication control device 21 creates and reads second messages 46, for example, CAN FD messages 46. The CAN FD messages 46 can contain from 0 to 64 data bytes, which are also transmitted at a significantly faster data rate than a Classical CAN message. In particular, the communication control device 21 is designed like a conventional CAN FD controller.

[0042] The transceiver 22 can be designed as a conventional CAN transceiver according to ISO 11898-1:2015 or CAN FD transceiver. The transceivers 12, 32 can be designed to provide messages 45 according to the CAN XL format or messages 46 according to the current CAN FD format to or receive them from the associated communication control device 11, 31, as required.

[0043] With the two subscriber stations 10, 30, the formation and then transmission of messages 45 with the CAN XL format as well as the reception of such messages 45 is possible.

[0044] Fig. 2 shows a CAN XL frame 450 for the message 45, as provided by the communication control device 11 for the transmitting / receiving device 12 for transmission on the bus 40. In this case, the communication control device 11 creates the frame 450 in the present embodiment as compatible with CAN FD, as in Fig. 2 The same applies analogously to the communication control device 31 and the transmitting / receiving device 32 of the subscriber station 30.

[0045] According to Fig. 2 The CAN XL frame 450 for CAN communication on the bus 40 is divided into different communication phases 451, 452, namely an arbitration phase 451 and a data phase 452. The frame 450 has an arbitration field 453, a control field 454, a data field 455, a checksum field 456 for a checksum FCRC and a switching sequence ADS, and an acknowledgment field 457.

[0046] In the arbitration phase 451, using an identifier (ID) in the arbitration field 453, the subscriber stations 10, 20, 30 negotiate bit by bit to determine which subscriber station 10, 20, 30 wishes to send the message 45, 46 with the highest priority and will therefore receive exclusive access to the bus 40 of the bus system 1 for the next transmission time in the subsequent data phase 452. In the arbitration phase 451, a physical layer is used, similar to CAN and CAN-FD. The physical layer corresponds to the physical layer or layer 1 of the well-known OSI model (Open Systems Interconnection Model).

[0047] An important point during phase 451 is the use of the well-known CSMA / CR method, which allows simultaneous access of subscriber stations 10, 20, and 30 to bus 40 without destroying the higher-priority message 45, 46. This allows additional bus subscriber stations 10, 20, and 30 to be added to bus system 1 relatively easily, which is very advantageous.

[0048] The CSMA / CR method requires so-called recessive states on bus 40, which can be overwritten by other subscriber stations 10, 20, or 30 with dominant states on bus 40. In the recessive state, high-impedance conditions prevail at the individual subscriber stations 10, 20, or 30, which, in combination with the parasitics of the bus circuitry, results in longer time constants. This limits the maximum bit rate of today's CAN FD physical layer to approximately 2 megabits per second in real-world vehicle use.

[0049] In the data phase 452, in addition to a part of the control field 454, the payload of the CAN-XL frame or message 45 from the data field 455 as well as the checksum field 456 for the checksum FCRC and also a field DAS are sent, which is used to switch from the data phase 452 back to the data phase 451.

[0050] A sender of the message 45 begins sending bits of the data phase 452 to the bus 40 only when the subscriber station 10 as the sender has won the arbitration and the subscriber station 10 as the sender thus has exclusive access to the bus 40 of the bus system 1 for sending.

[0051] In general, the following different properties can be realized in the bus system with CAN XL compared to CAN or CAN FD: a) Adoption and, where necessary, adaptation of 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 procedure, b) Increasing the net data transmission rate, in particular to approximately 10 megabits per second, c) Increasing the size of the payload data per frame, in particular to approximately 4 kbyte or any other value.

[0052] As in Fig. 2 As shown, in the arbitration phase 451 as the first communication phase, the subscriber station 10 partially uses, in particular up to and including the FDF bit, a format known from CAN / CAN-FD according to ISO11898-1:2015. In contrast, the subscriber station 10 uses a CAN XL format, which is described below, starting with the FDF bit in the first communication phase and in the second communication phase, the data phase 452.

[0053] In the present embodiment, CAN XL and CAN FD are compatible. The res bit known from CAN FD, referred to below as the XLF bit, is used to switch from the CAN FD format to the CAN XL format. Therefore, the frame formats of CAN FD and CAN XL are identical up to the res bit. A receiver only recognizes the frame format being transmitted at the res bit. A CAN XL subscriber station, i.e., subscriber stations 10 and 30 in this case, also supports CAN FD.

[0054] Alternatively to the Fig. 2 In addition to the frame 450 shown, which uses an 11-bit identifier, a CAN XL Extended Frame Format is optionally available, which uses a 29-bit identifier. This is identical to the familiar CAN FD Extended Frame Format from ISO11898-1:2015, up to the FDF bit.

[0055] According to Fig. 2Frame 450 from the SOF bit up to and including the FDF bit is identical to the CAN FD Base Frame Format according to ISO11898-1:2015. Therefore, the known structure is not explained further here. Bits that are marked on their lower line in Fig. 2 are shown with a thick line are sent as dominant or '0' in frame 450. Bits that are on their upper line in Fig. 2 represented by a thick line are transmitted in frame 450 as recessive or '1'. In the CAN XL data phase 452, symmetric '1' and '0' levels are used instead of recessive and dominant levels.

[0056] Generally, two different stuffing rules are applied when generating frame 450. Up to the XLF bit in control field 454, the dynamic bit stuffing rule of CAN FD applies, so that an inverse stuff bit is inserted after every five consecutive identical bits. After a resXL bit in control field 454, a fixed stuffing rule applies, so that a fixed stuff bit is inserted after a fixed number of bits. Alternatively, instead of just one stuff bit, two or more bits can be inserted as fixed stuff bits, as described in more detail later.

[0057] In frame 450, the XLF bit follows directly after the FDF bit, which corresponds in position to the "res bit" in the CAN FD Base Frame Format, as mentioned above. If the XLF bit is sent as 1, i.e., recessive, it identifies frame 450 as a CAN XL frame. For a CAN FD frame, the communication controller 11 sets the XLF bit to 0, i.e., dominant.

[0058] After the XLF bit in frame 450, there is a resXL bit, which is a dominant bit for future use. The resXL must be sent as 0, i.e., dominant, for frame 450. However, if subscriber station 10 receives a resXL bit as 1, i.e., recessive, the receiving subscriber station 10 enters a protocol exception state, for example, as is the case with a CAN FD message 46 for res=1. Alternatively, the resXL bit could be defined the other way around, meaning it must be sent as 1, i.e., recessive. In this case, the receiving subscriber station enters the protocol exception state with a dominant resXL bit.

[0059] After the resXL bit, an ADS (Arbitration Data Switch) sequence follows in frame 450, in which a predetermined bit sequence is encoded. This bit sequence allows for a simple and secure switchover from the bit rate of the arbitration phase 451 (arbitration bit rate) to the bit rate of the data phase 452 (data bit rate). For example, the bit sequence of the ADS sequence consists of an AL1 bit, which is transmitted dominantly, i.e., 0. The AL1 bit is the last bit of the arbitration phase 451. Within the AL1 bit, the physical layer in the transceiver device 12, 22, 32 is switched. The two following bits, DH1 and DL1, are already transmitted at the data bit rate. Thus, the DH1 and DL1 bits in CAN XL are temporally short bits of the data phase 452.

[0060] Following the ADS sequence in frame 450 is a PT field that identifies the content of data field 455. The content specifies what type of information is contained in data field 455. For example, the PT field specifies whether data field 455 contains an Internet Protocol (IP) frame, a tunneled Ethernet frame, or something else.

[0061] The PT field is followed by a DLC field containing the data length code (DLC), which specifies the number of bytes in data field 455 of frame 450. The data length code (DLC) can have any value from 0 up to the maximum data field length of 455. In particular, if the maximum data field length is 2048 bits, the data length code (DLC) requires 11 bits, assuming that DLC = 0 means a data field length of 1 byte and DLC = 2047 means a data field length of 2048 bytes. Alternatively, a data field 455 of length 0 could be permitted, as in CAN, for example. Here, DLC = 0 would encode a data field length of 0 bytes. The maximum encodable data field length of 11 bits, for example, is then (2^11)-1 = 2047.

[0062] After the DLC field, a header checksum HCRC follows in frame 450. The header checksum HCRC is a checksum for securing the header of frame 450, i.e., all bits from the beginning of frame 450 with the SOF bit to the beginning of the header checksum HCRC, including all dynamic and optionally fixed stuff bits up to the beginning of the header checksum HCRC. The length of the header checksum HCRC and thus of the checksum polynomial according to the cyclic redundancy check (CRC) must be selected according to the desired Hamming distance. The data word to be protected by the header checksum HCRC is longer than 27 bits with a data length code (DLC) of 11 bits. Therefore, to achieve a Hamming distance of 6, the polynomial of the header checksum HCRC must be at least 13 bits long.

[0063] After the header checksum HCRC, the data field 455 follows in frame 450. The data field 455 consists of 1 to n data bytes, where n is, for example, 2048 bytes or 4096 bytes or any other value. Alternatively, a data field length of 0 is conceivable. The length of the data field 455 is encoded in the DLC field, as previously described.

[0064] After the data field 455, a frame checksum FCRC follows in the frame 450. The frame checksum FCRC consists of the bits of the frame checksum FCRC. The length of the frame checksum FCRC and thus of the CRC polynomial must be selected according to the desired Hamming distance. The frame checksum FCRC secures the entire frame 450. Alternatively, only the data field 455 can be secured with the frame checksum FCRC.

[0065] After the frame checksum FCRC, the DAS (Data Arbitration Switch) sequence follows in frame 450, in which a predetermined bit sequence is encoded. This bit sequence allows for a simple and secure switch from the data bit rate of data phase 452 to the arbitration bit rate of arbitration phase 451.

[0066] For example, the bit sequence of the DAS sequence consists of a recessive data bit DH2 followed by a dominant arbitration bit DL2. In this example, the bit rate can be switched on the edge between the two mentioned bits. The DAS field typically has three bits: the DH2 bit, the DL2 bit, and an AH1 bit. Of these bits, the first and last bits are transmitted as recessive, i.e., 1, and the middle bit is transmitted as dominant, i.e., 0.

[0067] Deviating from the previous example, in the present embodiment, the DAS sequence contains an FCP field, with which the subscriber stations 10, 30, in particular their format check modules 15, 35, are able to detect an offset of the bit stream in a received frame 450. The longer the bit pattern of the FCP field, the larger or stronger the offset that can be detected in the receiving subscriber station 10, 30. The most advantageous bit pattern for offset detection contains an even number of M bits, where the first M / 2 bits contain a 1 and the following M / 2 bits contain a 0. In the example of Fig. 2 With a 4-bit FCP field, the first two bits are sent as recessive, i.e. 1. The last two bits of the FCP field are sent as dominant, i.e. 0. Thus, the FCP field with four bits differs according to Fig. 2, due to the additional bits DH3, DL3, from the usual two bits at the beginning of the DAS field. However, the edge from recessive to dominant in the FCP field can be Fig. 2 perform the same function as in a conventional DAS field that does not have the bits DH3, DL3.

[0068] In general, it is possible that in the FCP field the first M / 2 bits contain a 0 and the following M / 2 bits contain a 1. With the FCP field, an offset of M-1 can be detected. This is explained below with respect to Fig. 3 described in more detail.

[0069] Following the DAS sequence, frame 450 is followed by the acknowledgment field 457, which begins with an RP field. The RP field contains a synchronization pattern (Sync Pattern) that allows a receiving subscriber station 10, 30 to recognize the start of the arbitration phase 451 after the data phase 452. The synchronization pattern allows receiving subscriber stations 10, 30 that do not know the correct length of the data field 455, for example, due to an incorrect header checksum (HCRC), to synchronize. These subscriber stations can then send a "Negative Acknowledge" to indicate the faulty reception. This is particularly important if CAN XL does not allow error frames 47 (Error Flags) in the data field 455.

[0070] After the RP field, the ACK field 457 contains several bits to confirm or not confirm a correct reception of the frame 450. In the example of Fig. 2An ACK bit, an ACK-dlm bit, a NACK bit, and a NACK-dlm bit are provided. The NACK bit and the NACK-dlm bit are optional bits. The receiving subscriber stations 10, 30 send the ACK bit as dominant if they have received frame 450 correctly. The transmitting subscriber station sends the ACK bit as recessive. Therefore, the bit originally sent in frame 450 on bus 40 can be overwritten by the receiving subscriber stations 10, 30. The ACK-dlm bit is sent as a recessive bit, which serves to separate it from other fields. The NACK bit and the NACK-dlm bit allow a receiving subscriber station to signal incorrect reception of frame 450 on bus 40. The function of the bits is the same as that of the ACK bit and the ACK-dlm bit.

[0071] After the acknowledgment field (ACK field) 457, an end-of-frame (EOF) field follows in frame 450. The bit sequence of the end-of-frame (EOF) serves to mark the end of frame 450. The end-of-frame (EOF) field ensures that a number of 8 recessive bits are sent at the end of frame 450. This is a bit sequence that cannot occur within frame 450. This allows subscriber stations 10, 20, and 30 to reliably detect the end of frame 450.

[0072] The end of field (EOF) has a length that varies depending on whether a dominant or recessive bit was seen in the NACK bit. If the transmitting station received the NACK bit as dominant, the end of field (EOF) has 7 recessive bits. Otherwise, the end of field (EOF) is only 5 recessive bits long.

[0073] After the end field (EOF) in frame 450 there follows an inter-frame space (IFS - Inter Frame Space), which is Fig. 2is not shown. This interframe spacing (IFS) is designed as in CAN FD according to ISO11898-1:2015.

[0074] Fig. 3 shows the basic structure of the subscriber station 10 with the communication control device 11, the transmitting / receiving device 12 and the format checking module 15, which is part of the communication control device 11. The subscriber station 30 is constructed in a similar manner as in Fig. 3 shown, however, the format checking module 35 is according to Fig. 1 arranged separately from the communication control device 31 and the transmitting / receiving device 32. Therefore, the subscriber station 30 will not be described separately.

[0075] According to Fig. 3In addition to the communication control device 11 and the transceiver device 12, the subscriber station 10 has a microcontroller 13, to which the communication control device 11 is assigned, and a system ASIC 16 (ASIC = Application-Specific Integrated Circuit), which can alternatively be a system base chip (SBC) on which several functions necessary for an electronic module of the subscriber station 10 are combined. In addition to the transceiver device 12, the system ASIC 16 contains a power supply device 17, which supplies the transceiver device 12 with electrical power. The power supply device 17 typically supplies a CAN_Supply voltage of 5 V. However, depending on requirements, the power supply device 17 can supply a different voltage with a different value. Additionally or alternatively, the power supply device 17 can be designed as a current source.

[0076] The format check module 15 has an insertion block 151 and an evaluation block 152, which are described in more detail below.

[0077] The transmitting / receiving device 12 also has a transmitting module 121 and a receiving module 122. Although the following always refers to the transmitting / receiving device 12, it is alternatively possible to provide the receiving module 122 in a separate device external to the transmitting module 121. The transmitting module 121 and the receiving module 122 can be constructed as in a conventional transmitting / receiving device 22. The transmitting module 121 can, in particular, have at least one operational amplifier and / or one transistor. The receiving module 122 can, in particular, have at least one operational amplifier and / or one transistor.

[0078] The transceiver device 12 is connected to the bus 40, more precisely to its first bus wire 41 for CAN_H or CAN-XL_H and its second bus wire 42 for CAN_L or CAN-XL_L. The voltage supply for the power supply device 17, which supplies the first and second bus wires 41, 42 with electrical energy, in particular the CAN supply voltage, is provided via at least one terminal 43. The connection to ground or CAN_GND is realized via a terminal 44. The first and second bus wires 41, 42 are terminated with a terminating resistor 49.

[0079] The first and second bus wires 41, 42 are connected in the transmitting / receiving device 12 not only to the transmitting module 121, which is also referred to as transmitter, and to the receiving module 122, which is also referred to as receiver, even if the connection in Fig. 3 not shown for simplicity.

[0080] During operation of the bus system 1, the transmitting module 121 converts a transmitting signal TXD or TxD of the communication control device 11 into corresponding signals CAN-XL_H and CAN-XL_L for the bus wires 41, 42 and transmits these signals CAN-XL_H and CAN-XL_L to the terminals for CAN_H and CAN_L on the bus 40.

[0081] The receiving module 122 forms from the signals CAN-XL_H and CAN-XL_L received from bus 40 according to Fig. 4 a receive signal RXD or RxD and forwards it to the communication control device 11, as shown in Fig. 3 shown. With the exception of an idle or standby state, the transmitting / receiving device 12 with the receiving module 122 always listens for a transmission of data or messages 45, 46 on the bus 40 during normal operation, regardless of whether the transmitting / receiving device 12 is the sender of the message 45 or not.

[0082] According to the example of Fig. 4The signals CAN-XL_H and CAN-XL_L have the dominant and recessive bus levels 401, 402, as known from CAN, at least in the arbitration phase 451. On the bus 40, a difference signal VDIFF = CAN-XL_H - CAN-XL_L is formed, which Fig. 5 is shown. The individual bits of the VDIFF signal with the bit time t_bt can be detected with a receive voltage of 0.7 V. In the data phase 452, the bits of the CAN-XL_H and CAN-XL_L signals are transmitted faster, i.e., with a shorter bit time t_bt, than in the arbitration phase 451. Thus, the CAN-XL_H and CAN-XL_L signals in the data phase 452 differ from the conventional CAN_H and CAN_L signals at least in their faster bit rate.

[0083] The sequence of states 401, 402 for the signals CAN-XL_H, CAN-XL_L in Fig. 4 and the resulting voltage curve VDIFF of Fig. 5serves only to illustrate the function of subscriber station 10. The sequence of data states for bus states 401, 402 can be selected as required.

[0084] In other words, the transmitting module 121 generates in a first operating mode according to Fig. 4 a first data state as bus state 402 with different bus levels for two bus wires 41, 42 of the bus line and a second data state as bus state 401 with the same bus level for the two bus wires 41, 42 of the bus line of the bus 40.

[0085] In addition, the transmit module 121 transmits the bits at a higher bit rate to bus 40 for the timing of the CAN-XL_H and CAN-XL_L signals in a second operating mode, which includes the data phase 452. The CAN-XL_H and CAN-XL_L signals can also be generated in the data phase 452 using a different physical layer than in CAN FD. This allows the bit rate in the data phase 452 to be increased even further than in CAN FD.

[0086] The format check module 15 from Fig. 3 , in particular its insertion block 151, serves to insert the FCP field into the frame 450 when the subscriber station 10 acts as the transmitter of the frame 450. In the example of Fig. 2 The insertion block 151 has inserted only a single FCP field into the frame 450. The FCP field is placed as late as possible in the frame 450 so that shifts at the end of the frame 450 can also be detected. A very advantageous placement is after the frame checksum FCRC, as in Fig. 2 shown as an example, since this is the last possible position.

[0087] The format check module 15 from Fig. 3In the present embodiment, the FCP field is configured such that it replaces the DH2 bit and the DL2 bit of the DAS field. To do this, the FCP field must be selected as 1100 or 111000, etc., to retain the DH2 / DL2 function. Thus, the FCP field not only serves to enable secure format checking but also as a synchronization edge before switching from the data phase 452 to the arbitration phase 451. The FCP field thus has two different functions. As a result, the FCP field generates as little data overhead as possible.

[0088] Optional is the format check module 15 from Fig. 3 designed to integrate the FCP field alternatively or additionally into the ADS field. Insertion block 151 can thus insert at least one FCP field into frame 450.

[0089] The evaluation block 152 of the format check module 15 of Fig. 3is used to check the format of the bit stream received from the bus 40 using the FCP field.

[0090] For example, if the FCP field has M = 4 bits, the insertion block 151 can insert the FCP field as "1100" or "0011." Consequently, the FCP field is transmitted as "1100" or "0011." If the receiving subscriber station 10 samples a different value for the FCP field using the evaluation block 152, the evaluation block 152 evaluates that a shift in the bit stream of frame 450 has occurred. With such a bit sequence in the FCP field, the receiving subscriber station 10 can reliably detect a shift of the bit stream received from bus 40 by M - 1 = 3 bits to the left or by M - 1 = 3 bits to the right using the evaluation block 152. This is illustrated in the table below. case Scanning result at receiving subscriber station Right shift by 3 bits 0xxx Right shift by 2 bits 00xx Right shift by 1 bit     100x No postponement    1100 Left shift by 1 bit   x110 Left shift by 2 bits xx11 Left shift by 3 bits xxx1

[0091] In the table, x represents any bit value, i.e., 0 or 1. The FCP field is transmitted as "1100," as indicated in the middle of the table. If there is no edge offset and thus no shift in the bit stream, the receiving station also samples the FCP field as "1100."

[0092] Above and below the transmitted field "1100," the table shows the cases in which the receiving subscriber station (receiving node) 10, which in this example is not a transmitter of frame 450, samples the bit stream offset due to an error. "Right shift by 3 bits" means that the view of the receiving subscriber station (receiving node) is offset by 3 bits, in this case, 3 bits late. Accordingly, the receiving subscriber station (receiving node) 10 samples the last bit of the transmitted FCP field as the first bit of the received FCP field. The other three bits of the received FCP field then have different values, denoted here by 'x'.

[0093] "Left shift by 1 bit" means that the view of the receiving subscriber station (receiving node) 10 is shifted by 1 bit, in this case, 1 bit too early. Accordingly, the receiving subscriber station (receiving node) 10 samples the first 3 bits of the transmitted FCP field as the last bits of the received FCP field.

[0094] As can be seen from the table, the value of the FCP field sampled by the receiving subscriber station (receiving node) 10 always differs from the expected value of the FCP field by at least one bit in the event of a shift, regardless of the value of the bits designated 'x'. Thus, the receiving subscriber station (receiving node) 10, in particular its format check module 15 and more precisely its evaluation block 152, can detect the shift, i.e., the error in the received bit stream. The evaluation block 152 outputs a corresponding message to the communication control device 11. Thus, the received frame 450 can be discarded in the event of an error. As a result, the communication control device 11 can send an error frame 47 to the bus 40.

[0095] According to another example of a fixed value for the FCP field of the present embodiment, the FCP field has 6 bits, so that M = 6 bits. Insertion block 151 thus inserts the FCP field as "111000" or "000111." Consequently, the FCP field is transmitted as "111000" or "000111." If the receiving subscriber station 10 (which is not a sender of the frame) samples a different value for the FCP field using evaluation block 152, evaluation block 152 evaluates that a bit stream shift has occurred. With such a bit sequence in the FCP field, the receiving subscriber station 10 can reliably detect a shift of the bit stream received from bus 40 by M - 1 = 5 bits to the left or right using evaluation block 152.

[0096] Of course, other fixed lengths of the FCP field and thus other fixed values ​​of the FCP field are conceivable.

[0097] According to a modification of the present embodiment, the FCP field has a variable content.

[0098] As an example of such variable content of the FCP field, the number of fixed stuff bits can be transmitted in the FCP field. The number of fixed stuff bits depends on the length of frame 450. If the width of the FCP field, i.e., the number of bits allocated for the FCP field in frame 450, is not sufficient to transmit the entire number of fixed stuff bits, only the lower-order bits of a fixed stuff bits counter can be transmitted.

[0099] As another example of such variable content of the FCP field, the number of frames 450 transmitted by a transmitting subscriber station (transmitting node) can be transmitted in the FCP field. The number of frames 450 transmitted by a transmitting node can also be referred to as a frame counter.

[0100] Fig. 6shows a frame 450_1 according to a second embodiment in which CAN XL and CAN FD are compatible. In this embodiment, the frame 450_1 and thus the CAN XL frame format differs from the frame 450 of Fig. 2 , as described below. Here are only the differences to the frame 450 of Fig. 2 described. Otherwise, the frames 450, 450_1 of the two embodiments are identical.

[0101] In frame 450_1 there are at least two FCP fields. In the example of Fig. 6 In frame 450_1, an FCP field FCP1 is inserted after the header checksum HCRC, and an FCP field FCP2 is inserted after the frame checksum FCRC. In frame 450_1, the FCP fields FCP1 and FCP2 also have a length of M = 4 bits, as an example. Of course, a different length can be selected for the FCP field. In particular, it is possible for the length, i.e., the number of bits, of the FCP fields FCP1 and FCP2 to be different.

[0102] In general, the insertion block 151 can be configured to insert an FCP field at any location within the frame 450_1. The evaluation block 152 is configured to search for the FCP field at the corresponding insertion locations and thus evaluate the received frame 450_1.

[0103] In particular, the insertion block 151 is configured to insert an FCP field multiple times into the frame 450_1 to be transmitted. For example, an FCP field with the same content can always be inserted after a predetermined number of data items, in particular after 128 bytes of data or any other value. Of course, other examples are conceivable.

[0104] Fig. 7 shows a frame 4500 according to a third embodiment, in which the frame formats of CAN XL and CAN FD are not compatible. In this embodiment, the frame 4500 and thus the CAN XL frame format differs from the frame 450 of Fig. 2 , as described below. Only the differences to the frame 450 of Fig. 2 described. Otherwise, the frames 450, 4500 of the two embodiments are identical.

[0105] In general, when generating frame 4500 according to the present embodiment, only the fixed stuffing rule is used, so that a fixed stuff bit is inserted after a fixed number of bits. Alternatively, instead of just one stuff bit, two or more bits can be inserted as fixed stuff bits. This results in a constant frame length or a constant length of frame 4500, given a known value of the data length code (DLC). This prevents various problems caused by dynamic stuff bits.

[0106] In frame 4500 according to the present embodiment, the identifier (ID) is no longer limited to a number of 11 bits or 29 bits as in CAN FD. The number k of bits of the identifier (ID) can be freely selected. However, the number k can alternatively be set to a fixed value. For a high net data rate, an ID with k = 8 bits is useful. This is sufficient to give each subscriber station 10, 20, 30 of bus system 1 a sufficient number of bus access priorities. Of course, a different value for k can be selected depending on the requirements and the number of different priorities in bus system 1.

[0107] The bits RRS, IDE, FDF, XLF of frame 450 of Fig. 2 are no longer required in frame 4500 and are omitted. This saves 4 bits, thus reducing the frame overhead. This increases the net data rate in bus system 1.

[0108] The end of field (EOF) in frame 4500 only has five bits if the NACK bit is dominant. If, however, the NACK bit is recessive, the end of field (EOF) has three bits. This ensures that six recessive bits are sent at the end of frame 4500. This number of recessive bits cannot occur anywhere else in a valid frame 4500 if, in the arbitration phase 451, a fixed stuff bit is inserted after five identical bits. Alternatively, there could be more than six bits. In particular, the number of EOF bits must be adjusted to the number of bits after which a fixed stuff bit is inserted.

[0109] The interframe spacing (IFS) does not require a minimum length in the 4500 frame. In particular, the interframe spacing (IFS) can have a length of 0. In such a case, two 4500 frames are sent seamlessly one after the other. However, an interframe spacing (IFS) with a number of, for example, 1 bit is also useful to increase the robustness of bus system 1 compared to the previously mentioned case. The seven recessive bits between two 4500 frames allow a new subscriber station on bus 40 to synchronize more reliably.

[0110] According to a fourth embodiment, the FCP field is used as a fixed stuff bit. In other words, instead of a fixed stuff bit, the insertion block 151 is configured to insert an FCP field into the frame 450. In such a case, a short FCP field, for example, with a length of M = 2 bits, is sufficient, since only a small shift can occur between two stuff bits.

[0111] Thus, in the present embodiment, the FCP field also has two different functions, namely stuff bit and format check.

[0112] An FCP field with a length of M = 2 bits causes very little data overhead, or even no data overhead at all. This is explained in more detail below.

[0113] In the present embodiment, an FCP field with constant content is always used instead of a fixed stuff bit. The bit pattern in the FCP field is selected by the insertion block 151 such that the FCP field contains a synchronization edge. If CAN XL synchronizes to falling edges, a value of "10" would be advantageous for the FCP field. If CAN XL were to synchronize to the rising edge, a value of "01" would be advantageous for the FCP field.

[0114] With fixed stuff bits, in the worst case, a falling edge for synchronization is only present after every second stuff bit. Since synchronization is always possible with an FCP field, the distance between two FCP fields can be twice as large as the distance between two fixed stuff bits without impairing the synchronization of a receiving subscriber station 10, 30 (receiving node).

[0115] Since the FCP field has 2 bits but occurs only half as often as a fixed stuff bit, the data overhead caused by the FCP field is identical to the data overhead caused by fixed stuff bits.

[0116] The great advantage of the FCP field is that its content is constant. This allows for reliable detection of shifts in the data stream. In the example described with M = 2 bits, shifts of 1 bit in the receiving subscriber station 10, 30 (receiving node) can be reliably detected. Because the FPC field occurs so frequently in the frame, shifts can be detected immediately and effectively. This allows an error in the received frame 450 to be detected very quickly, and the transmission of frame 450 can be aborted quickly. This contributes to faster transmission of user data in bus system 1.

[0117] According to a modification of the present embodiment, the receiving subscriber station 10, 30 (CAN XL receiving node) can perform resynchronization only on the edges in the FCP field, instead of resynchronizing on every falling edge. By limiting resynchronization to the necessary edges, the risk of the receiving subscriber station 10, 30 (CAN XL receiving node) synchronizing to a disturbed edge and thus introducing an error is reduced.

[0118] The great advantage of this modification of the present embodiment is that the number of resynchronization errors decreases because now the edges in the FCP field must be explicitly disturbed in order to achieve missynchronization.

[0119] According to a fifth embodiment, the FCP field is again used as a fixed stuff bit, as in the previous embodiment. However, in this embodiment, an FCP field with variable content is always used instead of a fixed stuff bit. Thus, in this embodiment, the FCP field also has two different functions: stuff bit and format check.

[0120] Insert block 151 always selects an FCP field matching the value of the stuff bit. Since a stuff bit can have two values, namely 0 or 1, two different FCP fields are assumed. Thus, insert block 151 can either insert an FCP field FCP_A with the value "01" or an FCP field FCP_B with the value "10."

[0121] Therefore, the insertion block 151 inserts an FCP field depending on the value of the potential stuff bit. For example, the FCP field FCP_A would be inserted and sent if the stuff bit is 0. If the stuff bit is 1, the FCP field FCP_B would be inserted and sent.

[0122] The principle of the variable content of the FCP field is of course applicable to the creation of other FCP fields for the insertion block 151.

[0123] According to a sixth embodiment, the AH1 bit is used as an additional or sole FCP field. This is possible if the AH1 bit is not evaluated otherwise according to the current state of CAN XL standardization. Currently, the AH1 bit only serves to provide time in the transmitting / receiving device 12, 32 for the physical layer to switch from the data phase 452 to the arbitration phase 451.

[0124] In such a case, the receiving node can signal the physical layer switchover to the transmitting / receiving device 12, 32, for example, via a TXD line. This is possible because the receiving node does not use its TXD line for transmitting. This is not possible in the transmitting node, because the transmitting node uses its TXD line for transmitting.

[0125] Consequently, the receiving node or subscriber station 10, as the receiving subscriber station, can evaluate, i.e., sample, the AH1 bit with its evaluation block 152. Since the AH1 bit has a constant value, it also serves to check the format of the received frame (format check). The AH1 bit helps detect whether the receiving node is sampling the bit stream with an offset. This allows the format check of the received frame to be performed reliably or further enhanced with additional FCP fields.

[0126] The advantage of evaluating the AH1 bit is that the format check of the received frame 450 does not cause any data overhead. Thus, in the present embodiment, the FCP field also has two different functions: the function of the previous AH1 bit and format checking.

[0127] All previously described embodiments of the subscriber stations 10, 20, 30, the bus system 1, and the method implemented therein can be used individually or in all possible combinations. In particular, all features of the previously described embodiments and / or modifications thereof can be combined as desired. Additionally or alternatively, the following modifications are conceivable.

[0128] Although the invention has been described above using the CAN bus system as an example, the invention can be applied to any communication network and / or communication method that uses two different communication phases, in which the bus states generated for the different communication phases differ. In particular, the invention is applicable to the development of other serial communication networks, such as Ethernet and / or 100 Base-T1 Ethernet, fieldbus systems, etc.

[0129] In particular, bus system 1 according to the exemplary embodiments can be a communications network in which data can be transmitted serially at two different bit rates. It is advantageous, but not a mandatory requirement, that exclusive, collision-free access of a subscriber station 10, 20, 30 to a common channel is guaranteed in bus system 1, at least for certain periods of time.

[0130] The number and arrangement of subscriber stations 10, 20, 30 in bus system 1 of the exemplary embodiments is arbitrary. In particular, subscriber station 20 can be omitted from bus system 1. It is possible for one or more of subscriber stations 10 or 30 to be present in bus system 1. It is conceivable for all subscriber stations in bus system 1 to be configured identically, i.e., only subscriber station 10 or only subscriber station 30 to be present.

Claims

1. Subscriber station (10; 30) for a serial bus system (1), having a communication control device (11; 31) for controlling communication between the subscriber station (10; 30) and at least one other subscriber station (10; 20; 30) of the bus system (1), and a transmitting / receiving device (12; 32) for transmitting a transmission signal (TXD) generated by the communication control device (11; 31) onto a bus (40) of the bus system (1), with the result that, for a message (45) exchanged between subscriber stations (10, 20, 30) of the bus system (1), the bit time (t_bt) of a signal transmitted onto the bus (40) in the first communication phase (451) can differ from a bit time (t_bt) of a signal transmitted in the second communication phase (452), characterized in that the communication control device (11; 31) is configured to generate the transmission signal (TXD) according to a frame (450; 450_1; 4500) and to insert in the frame (450; 450_1; 4500) at least one field (FCP; FCP_1; FCP_2) which is configured for checking whether the bit stream of the frame (450; 450_1; 4500) is offset by at least one bit compared with the expected frame (450; 450_1; 4500) in a subscriber station (10; 20; 30) of the bus system (1) which receives the frame (450; 450_1; 4500) but is not a transmitter of the frame (450; 450_1; 4500), and wherein the communication control device (11; 31) in the case where the subscriber station (10; 30) is not a transmitter of the frame (450; 450_1; 4500) is configured to use the at least one field (FCP; FCP_1; FCP_2) for checking whether the bit stream of the received frame is offset by at least one bit compared with the expected frame (450; 450_1; 4500).

2. Subscriber station (10; 30) according to Claim 1, wherein the communication control device (11; 31) is configured to insert the at least one field (FCP; FCP_2) after a data field (455) in the frame (450; 450_1; 4500), in particular to insert the at least one field (FCP; FCP_2) in the frame (450; 450_1; 4500) after a frame checksum (FCRC) which has been formed over all bits in the frame (450; 450_1; 4500).

3. Subscriber station (10; 30) according to Claim 1 or 2, wherein the communication control device (11; 31) is configured to insert the at least one field (FCP _1) before a data field (455) in which payload data of the frame (450; 450_1; 4500) are inserted.

4. Subscriber station (10; 30) according to any of the preceding claims, wherein the communication control device (11; 31) is configured to configure and / or arrange the at least one field (FCP_1) in such a way that the content of the at least one field (FCP_1) is to be used in a receiving subscriber station (10; 30) not only for the function of checking the offset of the bit stream, but also for a function differing therefrom.

5. Subscriber station (10; 30) according to any of the preceding claims, wherein the communication control device (11; 31) is configured to insert one of the fields (FCP; FCP_1; FCP_2) into the frame (450; 450_1; 4500) always after a fixed number of bits.

6. Subscriber station (10; 30) according to any of the preceding claims, wherein the communication control device (11; 31) is configured to insert the at least one field (FCP; FCP_1; FCP_2) as a fixed stuff bit in the frame (450; 450_1; 4500), and wherein the communication control device (11; 31) is configured to insert all fixed stuff bits into the frame (450; 450_1; 4500) according to a fixed bit stuffing rule according to which a fixed stuff bit is to be inserted after a fixed number of bits.

7. Subscriber station (10; 30) according to Claim 6, wherein the communication control device (11; 31) is configured to choose the value of the field (FCP; FCP_1; FCP_2) depending on the value that would have to be chosen for the stuff bit so that an inverse stuff bit is inserted in the frame (450; 450_1; 4500) after five identical bits in succession.

8. Subscriber station (10; 30) according to any of Claims 1 to 6, wherein the communication control device (11; 31) is configured to use the same value for all of the fields (FCP; FCP_1; FCP_2) in the frame (450; 450_1; 4500).

9. Subscriber station (10; 30) according to Claim 8, wherein the communication control device (11; 31) is configured to use an even number of M bits for the at least one field (FCP; FCP_1; FCP_2), wherein the first half of the M bits each have the same first value, and wherein the second half of the M bits each have the same second value, which is inverse with respect to the first value.

10. Subscriber station (10; 30) according to Claim 8, wherein the communication control device (11; 31) is configured to insert in the at least one field (FCP; FCP_1; FCP_2) at least the least significant bits of the number of fixed stuff bits inserted in the frame (450; 450_1; 4500).

11. Subscriber station (10; 30) according to Claim 8, wherein the communication control device (11; 31) is configured to insert in the at least one field (FCP; FCP _1; FCP _1) at least the least significant bits of the number of frames (450; 450_1; 4500) which have already been transmitted onto the bus (40) by the communication control device (11; 31).

12. Subscriber station (10; 30) according to any of the preceding claims, wherein the communication control device (11; 31) is configured, after a switching of the second communication phase (452) to the first communication phase (451), to provide a bit (AH1) during which the transmitting / receiving device (12; 32) has time for the switching to the second communication phase (452), and wherein the communication control device (11; 31) is configured, in the case where the subscriber station (10; 20; 30) of the bus system (1) receives the frame (450; 450_1; 4500) but is not a transmitter of the frame (450; 450_1; 4500), to use the bit (AH1) for checking whether the bit stream of the received frame (450; 450_1; 4500) is offset by at least one bit compared with the expected frame (450; 450_1; 4500).

13. Subscriber station (10; 30) according to any of the preceding claims, wherein the frame (450; 450_1) formed for the message (45) is designed as compatible with CAN FD, and wherein negotiation takes place in the first communication phase (451) in order to determine which of the subscriber stations (10, 20, 30) of the bus system (1) receives at least temporarily exclusive, collision-free access to the bus (40) in the subsequent, second communication phase (452).

14. Bus system (1), having a bus (40), and at least two subscriber stations (10; 20; 30) which are connected to one another via the bus (40) in such a way that they can communicate serially with one another and at least one subscriber station (10; 30) of which is a subscriber station (10; 30) according to any of the preceding claims.

15. Method for communicating in a serial bus system (1), wherein the method is carried out using a subscriber station (10; 30) of the bus system (1), which subscriber station has a communication control device (11; 31) and a transmitting / receiving device (12; 32), wherein the method has the steps of controlling, using the communication control device (11; 31), communication between the subscriber station (10; 30) and at least one other subscriber station (10; 20; 30) of the bus system (1), and transmitting, using the transmitting / receiving device (12; 32), a transmission signal (TXD) generated by the communication control device (11; 31) onto a bus (40) of the bus system (1), with the result that, for a message (45) exchanged between subscriber stations (10, 20, 30) of the bus system (1), the bit time (t_bt) of a signal transmitted onto the bus (40) in the first communication phase (451) can differ from a bit time (t_bt) of a signal transmitted in the second communication phase (452), characterized in that the communication control device (11; 31) generates the transmission signal (TXD) according to a frame (450; 450_1; 4500) and inserts into the frame (450; 450_1; 4500) at least one field (FCP; FCP_1; FCP_2) which is configured for checking whether the bit stream of the frame (450; 450_1; 4500) is offset by at least one bit compared with the expected frame (450; 450_1; 4500) in a subscriber station (10; 20; 30) of the bus system (1) which receives the frame (450; 450_1; 4500) but is not a transmitter of the frame (450; 450_1; 4500), with the result that a communication control device (11; 31) of the bus system (1) in the case where the subscriber station (10; 30) is not a transmitter of the frame (450; 450_1; 4500) can use the at least one field (FCP; FCP_1; FCP_2) for checking whether the bit stream of the received frame is offset by at least one bit compared with the expected frame (450; 450_1; 4500).