TRANSMIT / RECEIVE DEVICE AND COMMUNICATION CONTROL DEVICE FOR A PARTICIPANT STATION OF A SERIAL BUS SYSTEM AND METHOD FOR COMMUNICATION IN A SERIAL BUS SYSTEM

Description

Technical field

[0001] The present invention relates to a transmitting / receiving device and a communication control device for a subscriber station of a serial bus system and a method for communication in a serial bus system that operates with high data rate and high error robustness. State of the art

[0002] For communication between sensors and control units, for example in vehicles, a bus system is frequently used in which data is transmitted as messages in the standard ISO 11898-1:2015 as a CAN protocol specification with CAN FD. The messages are transmitted as analog signals between the bus participants of the bus system, such as sensors, control units, encoders, etc.

[0003] Each participant in the bus system is connected to the bus via a transceiver. The transceiver contains at least one receiver comparator that receives the analog signals from the bus and converts them into a digital signal. The content of the digital signal can be interpreted by a communication control unit using its protocol controller. The communication control unit can also generate a signal for transmission on the bus and send it to the bus via the transceiver. In this way, information can be exchanged between the bus participants.

[0004] To enable higher bitrate data transmission over the bus compared to CAN, the CAN FD and CAN XL message formats incorporate an option to switch to a higher bitrate within a message. These techniques increase the maximum possible data rate by using a higher clock frequency in the data fields compared to CAN. This increases the maximum possible data rate for CAN FD frames and CAN FD messages beyond 1 Mbit / s. Furthermore, the payload length is extended from 8 to up to 64 bytes. A similar approach applies to CAN XL, which aims to increase data transmission speeds to, for example, 10Base-T1S Ethernet and to extend the payload length from up to 64 bytes, a previously achievable limit with CAN FD. This allows the robustness of the CAN or CAN FD-based communication network to be maintained to a significant advantage.

[0005] For transmission at the higher bit rate, the existing operating mode of the transmit / receive device must be switched from a mode for transmission at the lower bit rate (operating mode Z_SL) to another operating mode. It is important to consider that during transmission at the higher bit rate, only one of the participating stations in the bus system is the sender of the message, while all other participating stations are only receivers. Therefore, when signaling the operating mode for the higher bit rate, it must be possible to distinguish whether the participating stations are only receivers (operating mode Z_F_RX) or also senders (operating mode Z_F_TX) in order to switch the operating mode of the transmit / receive device accordingly.

[0006] It is conceivable that the communication control unit of the transmitting / receiving device serially communicates the information about which operating mode the transmitting / receiving device is to be switched to using a pulse pattern with a different number of bits.

[0007] However, evaluating such pulse patterns is complex. Furthermore, transmitting the pulse patterns takes time. This means that the individual pulses of the pattern must either be very short so that they can all be transmitted within a single bit, or that additional bits must be inserted into the frame to allow enough time to transmit the pulse patterns. Since short pulses could be mistaken for interference, their use is a disadvantage.

[0008] DE 10 2018 203 707 A1 shows a transceiver for a bus system and an operating procedure for it. However, no switching between operating modes of the transceiver is shown, in which the communication control unit of the transceiver signals with only one pulse via a connection for a received signal generated by the transceiver that the operating mode of the transceiver is to be switched. Disclosure of the invention

[0009] Therefore, the object of the present invention is to provide a transmit / receive device and a communication control device for a subscriber station of a serial bus system, and a method for communication in a serial bus system, which solve the aforementioned problems. In particular, a transmit / receive device and a communication control device for a subscriber station of a serial bus system, and a method for communication in a serial bus system, are to be provided in which the switching of the operating mode of the transmit / receive device can be carried out with high robustness and optimized timing.

[0010] The problem is solved by a transmit / receive device for a participant station of a serial bus system with the features of claim 1. The transmit / receive device has a first connection for receiving a transmit signal from a communication control unit, a transmit module for sending the transmit signal to a bus of the bus system, in which the bus system uses at least a first communication phase and a second communication phase for exchanging messages between participant stations of the bus system, a receive module for receiving the signal from the bus, wherein the receive module is configured to generate a digital receive signal from the signal received from the bus, and a second connection for sending the digital receive signal to the communication control unit and for receiving an operating mode switching signal from the communication control unit.and an operating mode switching block for evaluating the operating mode switching signal received at the second terminal from the communication control device and the transmit signal, wherein the operating mode switching block is configured to switch the transmit module and / or the receive module into one of at least three different operating modes depending on a result of the evaluation, as described in claim 1.

[0011] The transmit / receive device can reliably determine which of two possible operating modes to switch to using only a single pulse as a signal. This makes the switching condition for changing from operating mode Z_SL of the first communication phase to one of the two operating modes Z_F_RX or Z_F_TX of a second communication phase more robust, as it is less susceptible to interference.

[0012] Furthermore, the signaling and its evaluation in the transceiver are so reliable that switching, particularly to the Z_F_TX operating mode, does not occur accidentally, for example, due to a fault on the RxD line. As a result, the bus remains undisturbed. The evaluation performed by the transceiver to determine the switching condition combines the values ​​at the first and second terminals of the communication control unit, thus increasing the robustness of the transceiver's operating mode switching.

[0013] Naturally, the signaling and its evaluation in the transmitting / receiving device can also be used if it is only necessary to switch to one operating mode, for example at the transition from the second communication phase to the first communication phase.

[0014] Furthermore, the transceiver can maintain a CAN-like arbitration in one of the communication phases while still significantly increasing the transmission rate compared to CAN or CAN FD. This is achieved by using two communication phases with different bit rates and reliably indicating to the transceiver the start of the second communication phase, in which the user data is transmitted at a higher bit rate than in the arbitration phase. Therefore, the transceiver can reliably switch from the operating mode of the first communication phase to the specified or desired operating mode of the second communication phase, or back again. As a result, a significant increase in the bit rate and thus the transmission speed from sender to receiver is possible.However, this also ensures a high level of fault tolerance.

[0015] The procedure performed by the transmitting / receiving device can also be used if the bus system also contains 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.

[0016] Further advantageous configurations of the transmitting / receiving device are specified in the dependent claims.

[0017] The mode-switching signal received at the second terminal may be a pulse with a value inverse of a value of the digital receive signal. The mode-switching block is configured to switch the receive module from the first operating mode to the second operating mode when the switching signal contains the pulse and the value of the transmit signal corresponds to the value of the pulse. The mode-switching block is also configured to switch the transmit and receive modules from the first operating mode to the third operating mode when the switching signal contains the pulse and the value of the transmit signal is inverse of the value of the pulse. It is conceivable that the transmit / receive device in the second operating mode is not the sender of the message in the second communication phase, and that the transmit / receive device in the third operating mode is the sender of the message in the second communication phase.

[0018] The operating mode switching block can be designed to perform the switching of the operating mode, at least when switching from the second communication phase to the first communication phase, if an edge between different bus states occurs in the received signal output by the receiving module and the transmitting / receiving device is not the sender of the message.

[0019] The operating mode switching block can be designed to switch off the transmitting module in an operating mode of the second communication phase in which the transmitting / receiving device is not the sender of the message.

[0020] The operating mode switching block may be designed to switch the operating mode, at least when switching from the second communication phase to the first communication phase, if the transmit / receive device is the sender of the message in the second communication phase and an edge between different bus states occurs in the transmitted signal.

[0021] The aforementioned problem is further solved by a communication control device for a participant station of a serial bus system with the features of claim 11. The communication control device has a communication control module for generating a transmit signal for controlling communication between the participant station and at least one other participant station of the bus system, in which the bus system uses at least a first communication phase and a second communication phase for exchanging messages between participant stations of the bus system, a first connection for sending the transmit signal to a transmit / receive device configured for sending the transmit signal to a bus of the bus system, and a second connection for receiving a digital receive signal from the transmit / receive device, wherein the communication control device is configured for generating an additional signal.which indicates to the transmitting / receiving device that it is to switch from the current operating mode to another operating mode of at least two different operating modes, and which additionally implements internal communication between the communication control module and the transmitting / receiving device for a duration that can be preset in the communication control module and an operating mode switching block of the transmitting / receiving device, and wherein the communication control module is configured to send the additional signal to the transmitting / receiving device via the second connection and simultaneously signal to the transmitting / receiving device, together with the transmit signal sent at the first connection, into which of the operating modes the transmitting / receiving device is to be switched, as described in claim 11.

[0022] The communication control unit offers the same advantages as previously mentioned in relation to the transmitting / receiving unit.

[0023] The transmitter module may be configured to drive bits of the signals onto the bus in the first communication phase with a first bit time that is at least ten times greater than the second bit time of the bits driven onto the bus by the transmitter module in the second communication phase. In this case, the operating mode switching signal via the second terminal can have a pulse with a pulse duration that is shorter than the first bit time and longer than the second bit time, to signal that the operating mode switching is to be performed. According to another embodiment, the operating mode switching signal via the second terminal has at least one pulse with a pulse duration that is approximately equal to or shorter than the second bit time.

[0024] According to one option, the signal received by the bus in the first communication phase is generated with a different physical layer than the signal received by the bus in the second communication phase.

[0025] It is conceivable that in the first communication phase, it is negotiated which of the participating stations of the bus system will receive at least temporary exclusive, collision-free access to the bus in the subsequent second communication phase.

[0026] The previously described transmit / receive device and the previously described communication control device can be part of a subscriber station in a bus system, which also includes a bus and at least two subscriber stations that are interconnected via the bus in such a way that they can communicate serially with each other. In this case, at least one of the at least two subscriber stations has a previously described transmit / receive device and a previously described communication control device.

[0027] The aforementioned problem is further solved by a method for communication in a serial bus system according to claim 15. The method is implemented with a transmit / receive device of a subscriber station for a bus system, in which at least a first communication phase and a second communication phase are used for exchanging messages between subscriber stations of the bus system, wherein the subscriber station has a transmit module, a receive module, an operating mode switching block, a first terminal and a second terminal, and wherein the method comprises the steps of receiving, with the receive module, a signal from the bus of the bus system, generating, with the receive module, a digital receive signal from the signal received from the bus and outputting the digital receive signal at the second terminal, and evaluating, with the operating mode switching block.a mode switching signal received at the second terminal of the communication control unit and a transmit signal received at the first terminal of the communication control unit, and switching, with the mode switching block, the transmit module and / or the receive module, depending on a result of the evaluation into one of at least three different operating modes, as described in claim 15.

[0028] The procedure offers the same advantages as previously mentioned in relation to the transmitting / receiving equipment and / or the communication control equipment.

[0029] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention. Drawings

[0030] The invention is described in more detail below with reference to the accompanying drawing and by means of exemplary embodiments. The drawing shows: Fig. 1 a simplified block diagram of a bus system according to a first embodiment; Fig. 2 a diagram illustrating the structure of messages that can be sent by participant stations of the bus system according to the first embodiment; Fig. 3 a simplified schematic block diagram of a participant station of the bus system according to the first embodiment; Fig. 4 bis Fig. 7 a temporal sequence of signals according to the first embodiment for a time phase in which a first operating mode (Z_SL) of the transmitting / receiving device, which is switched on in an arbitration phase (first communication phase), is switched to an operating mode (Z_F, more precisely Z_F_TX) of the transmitting / receiving device in which the transmitting / receiving device acts as a transmitter in a data phase (second communication phase); and Fig. 8 und Fig. 9 a temporal progression of signals accordingly Fig. 4 bis Fig. 7 in a transmitting / receiving device that is switched from the operating mode (Z_SL) of the arbitration phase (first communication phase) to an operating mode (Z_F, more precisely Z_F_RX) in which the transmitting / receiving device only acts as a receiver in the data phase (second communication phase).

[0031] In the figures, identical or functionally equivalent elements are provided with the same reference symbols unless otherwise specified. Description of the exemplary implementations

[0032] Fig. 1 Figure 1 shows as an example a bus system 1, which is designed in a fundamental way for a CAN bus system, a CAN FD bus system, a CAN FD successor bus system, and / or variations thereof, as described below.

[0033] The bus system 1 can be used in a vehicle, especially a motor vehicle, an aircraft, etc., or in a hospital, etc.

[0034] In Fig. 1 Bus system 1 has a multitude of terminal stations 10, 20, 30, each connected to a bus 40 with a first bus wire 41 and a second bus wire 42. The bus wires 41 and 42 can also be called CAN_H and CAN_L, respectively, and serve for electrical signal transmission after coupling the dominant levels or generating recessive levels for a signal in the transmit state. Messages 45 and 46 in the form of signals can be transmitted serially between the individual terminal stations 10, 20, and 30 via bus 40. The terminal stations 10, 20, and 30 are, for example, control units, sensors, display devices, etc., of a motor vehicle.

[0035] As in Fig. 1 As shown, subscriber station 10 has a communication control unit 11, a transceiver 12, and a switching block 15. Subscriber station 20, on the other hand, has a communication control unit 21 and a transceiver 22. Subscriber station 30 has a communication control unit 31, a transceiver 32, and a switching block 35. The transceivers 12, 22, and 32 of subscriber stations 10, 20, and 30 are each directly connected to bus 40, even though this is shown in Fig. 1 is not illustrated.

[0036] At each subscriber station 10, 20, 30, the messages 45, 46 are encoded as frames and exchanged bit-by-bit via a TXD line and an RXD line between the respective communication control unit 11, 21, 31 and the associated transmit / receive units 12, 22, 32. This is described in more detail below.

[0037] The communication control devices 11, 21, 31 each serve to control communication between the respective subscriber station 10, 20, 30 via bus 40 with at least one other subscriber station of the subscriber stations 10, 20, 30 that are connected to bus 40.

[0038] The communication control units 11, 31 create and read initial messages 45, which are, for example, modified CAN messages 45, also referred to below as CAN XL messages 45. These modified CAN messages 45 or CAN XL messages 45 are based on a CAN FD successor format, which, with regard to Fig. 2 is described in more detail. The communication control devices 11, 31 can also be configured to provide or receive a CAN XL message 45 or a CAN FD message 46 for the transmit / receive devices 12, 32, as required. The communication control devices 11, 31 thus create and read a first message 45 or a second message 46, the first and second messages 45, 46 differing in their data transmission standard, namely in this case CAN XL or CAN FD.

[0039] The communication control unit 21 can be implemented like a conventional CAN protocol controller or CAN controller according to ISO 11898-1:2015, in particular like a CAN FD-tolerant Classical CAN controller or a CAN FD controller. The communication control unit 21 creates and reads secondary messages 46, for example, Classical CAN messages or CAN FD messages 46. 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 the latter case, the communication control unit 21 is implemented like a conventional CAN FD controller.

[0040] The transceiver units 12 and 32 can be implemented as CAN XL transceivers, with the exception of the differences described in more detail below. The transceiver units 12 and 32 can also be implemented as conventional CAN FD transceivers, either additionally or alternatively. The transceiver unit 22 can be implemented as either a conventional CAN transceiver or a CAN FD transceiver.

[0041] With the two participant 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.

[0042] Fig. 2 Figure 45 shows a CAN XL frame 450 as sent by the transmit / receive device 12 or the transmit / receive device 32. The CAN XL frame 450 is divided into different communication phases 451 to 455 for CAN communication on bus 40: an arbitration phase 451, a first switching phase 452 (located at the end of the arbitration phase 451), a data phase 453, a second switching phase 454 (located at the end of the data phase 453), and a frame end phase 455.

[0043] In arbitration phase 451, for example, a bit is sent at the beginning, also called the SOF bit, which indicates the start of the frame. Also in arbitration phase 451, an identifier, for example with 11 bits, is sent to identify the sender of message 45. During arbitration, the identifier is used to negotiate bit-by-bit between participating stations 10, 20, and 30 which station wants to send message 45, 46 with the highest priority and therefore receives exclusive access to bus 40 of bus system 1 for sending during switching phase 452 and the subsequent data phase 453.

[0044] In the first switching phase 452, the switch from the arbitration phase 451 to the data phase 453 is prepared in the present embodiment. The switching phase 452 can have a bit AL1, which has the bit duration T_B1 of a bit in the arbitration phase 451 and is transmitted with the physical layer of the arbitration phase 451. The physical layer corresponds to the physical layer or layer 1 of the well-known OSI model (Open Systems Interconnection model).

[0045] In data phase 453, following a DH1 bit and a DL1 bit, an 8-bit data field identifier can be sent, identifying the type of content in the data field. For example, the data field identifier could contain the value 9, indicating that the data field contains a data packet structured according to Internet Protocol version 4 (IPv4). Following the data field identifier, an 11-bit data length code can be sent, which can then take values ​​from 1 to 2048 or any other value in increments of 1. The data length code can alternatively have fewer or more bits, allowing for different value ranges and increments. This is followed by other fields, such as the header checksum field. Afterward, the payload data of the CAN XL frame 450 is transmitted.Message 45 is sent, which can also be referred to as the data field of message 45. The payload can contain data corresponding to the value range of the data length code, for example, up to 2048 bytes, a larger number of bytes, or any other arbitrary amount of data. At the end of data phase 453, for example, a checksum field can contain a checksum of the data from data phase 453 as well as the data from arbitration phase 451. The sender of message 45 can insert stuff bits as inverse bits into the data stream after a predetermined number of identical bits, in particular 10 identical bits. Specifically, the checksum is a frame checksum F_CRC, with which all bits of frame 450 up to the checksum field are secured. An FCP field with a predetermined value, for example 1100, can then follow.

[0046] In the second switching phase 454, the switch from the data phase 453 to the frame end phase 455 is prepared in the present embodiment. Protocol format information contained in at least one bit is sent, which is suitable for implementing the switch. The switching phase 454 can have a bit AH1 that has the bit duration T_B1 of a bit in the arbitration phase 451, but is sent with the physical layer of the data phase 453.

[0047] In the frame end phase 455, after two bits AL2 and AH2 in an end field, at least one acknowledge bit ACK can be present. This can be followed by a sequence of seven identical bits, indicating the end of the CAN XL frame 450. The at least one acknowledge bit ACK can be used to communicate whether a receiver has detected an error in the received CAN XL frame 450 or message 45.

[0048] At least in the arbitration phase 451 and the frame completion phase 455, a physical layer similar to that used in CAN and CAN-FD is employed. Additionally, in the first switching phase 452, a physical layer similar to that used in CAN and CAN-FD can be used at least partially, i.e., at the beginning. Additionally, in the second switching phase 454, a physical layer similar to that used in CAN and CAN-FD can be used at least partially, i.e., at the end.

[0049] An important point during phases 451, 455, at the beginning of phase 452, and at the end of phase 454 is the use of the well-known CSMA / CR protocol, which allows simultaneous access to bus 40 by participant stations 10, 20, and 30 without destroying the higher-priority message 45 or 46. This makes it relatively easy to add further bus participant stations 10, 20, and 30 to bus system 1, which is very advantageous.

[0050] The CSMA / CR method results in so-called recessive states on bus 40, which can be overwritten by other participant stations 10, 20, 30 with dominant states on bus 40.

[0051] Arbitration at the beginning of frame 450 or message 45, 46, and acknowledgment in the frame-end phase 455 of frame 450 or message 45, 46, are only possible if the bit time is significantly more than twice as long as the signal propagation time between any two subscriber stations 10, 20, 30 of bus system 1. Therefore, the bit rate in the arbitration phase 451, the frame-end phase 455, and at least partially in the switching phases 452, 454 is chosen to be slower than in the data phase 453 of frame 450. Specifically, the bit rate in phases 451, 452, 454, 455 is chosen to be 500 kbit / s, resulting in a bit time of approximately 2 µs, whereas the bit rate in the data phase 453 is chosen to be 5 to 10 Mbit / s or more. This results in a bit time of approximately 0.1 µs or less. Therefore, the bit time of the signal in the other communication phases 451, 452, 454, 455 is at least ten times greater than the bit time of the signal in the data phase 453.

[0052] A sender of message 45, for example, subscriber station 10, only begins transmitting bits of the switching phase 452 and the subsequent data phase 453 to bus 40 once subscriber station 10, as the sender, has won the arbitration and thus has exclusive access to bus 40 of bus system 1 for transmission. The sender can either switch to the faster bit rate and / or the other physical layer after part of the switching phase 452, or switch to the faster bit rate and / or the other physical layer only with the first bit, i.e., with the beginning of the subsequent data phase 453.

[0053] In general, the following different properties can be implemented in the CAN XL bus system compared to CAN or CAN FD: a) Adoption and, if necessary, adaptation of proven features 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 method, b) Increase of the net data transmission rate to approximately 10 megabits per second, and c) Increase of the size of the payload data per frame to approximately 2 kilobytes or to any other value.

[0054] Fig. 3 Figure 1 shows the basic structure of the subscriber station 10 with the communication control unit 11, the transmit / receive unit 12, and the switching block 15. The subscriber station 30 is constructed in a similar manner as shown in Figure 1. Fig. 3 The following is shown, except that block 35 is provided separately from the communication control unit 31 and the transmit / receive unit 32. Therefore, the subscriber station 30 and block 35 are not described separately. The functions of switching block 15 described below are identical in switching block 35.

[0055] According to Fig. 3 The communication control unit 11 also includes a communication control module 111, a transmit signal output driver 112, and an RxD port configuration module 113. The communication control unit 11 is designed as a microcontroller or incorporates a microcontroller. The communication control unit 11 processes signals from any application, for example, a control unit for an engine, a safety system for a machine or vehicle, or other applications.

[0056] Not shown in Fig. 3 However, it is a system ASIC (ASIC = Application-Specific Integrated Circuit), which can alternatively be a system base chip (SBC) on which several functions necessary for an electronic assembly of the subscriber station 10 are combined. The system ASIC can, among other things, incorporate the transceiver 12 and a power supply unit (not shown) that provides electrical power to the transceiver 12. The power supply unit typically provides a voltage CAN_Supply of 5 V. Depending on requirements, however, the power supply unit can provide a different voltage with a different value and / or be configured as a current source.

[0057] According to Fig. 3 The transmit / receive device 12 also has a transmit module 121, a receive module 122, a driver 123 for the transmit signal TxD, a receive signal output driver 124 and a driver 125 that outputs a signal RxD_TC to the switching block 15. Switching block 15 uses the RxD_TC signal, the TxD signal, and a signal S_SW, which is the output signal of the receiver module 122, to generate an operating state switching signal S_OP for switching the transmitter module 121. Additionally, switching block 15 uses the RxD_TC signal and the TxD and S_SW signals to generate an operating state switching signal S_OPT for switching the receive thresholds of the receiver module 122. Switching block 126 detects that a signal is present from the communication control module 111 by comparing the RxD_TC signal and the S_SW signal, because the RxD_TC signal contains at least one pulse transmitted by the communication control module 111. This is relevant to... Fig. 4 bis Fig. 9 described in more detail below.

[0058] The transmitter module 121 from Fig. 3 is also referred to as a transmitter. The receiving module 122 is also referred to as a receiver. The use of the TxD signal in the switching block 126 is optional, as is also the case in Fig. 3 The dashed line at signal TxD indicates this. Signals RxD and RxD_TC have the same waveform, but are separated by a driver 125.

[0059] The switching block 15 can be designed as a switching block, which in particular includes at least one flip-flop. The function of the switching block 15 is described below with regard to Fig. 4 bis Fig. 9 described in more detail.

[0060] Although the following text refers to the transmitter / receiver unit 12, it is alternatively possible to provide the receiver module 122 in a separate unit external to the transmitter module 121. The transmitter module 121 and the receiver module 122 can be constructed like a conventional transmitter / receiver unit 22. The transmitter module 121 can, in particular, include at least one operational amplifier and / or one transistor. The receiver module 122 can, in particular, include at least one operational amplifier and / or one transistor.

[0061] As in Fig. 3 As shown, the transceiver 12 is connected to bus 40, specifically its first bus wire 41 for CAN_H and its second bus wire 42 for CAN_L. Within the transceiver 12, the first and second bus wires 41 and 42 are connected to the transmit module 121 and the receive module 122, respectively. The power supply for the power supply unit, which provides electrical energy to the first and second bus wires 41 and 42, is provided in the usual manner. The connection to ground (CAN_GND) is also implemented in the usual way. Similarly, the termination of the first and second bus wires 41 and 42 with a terminating resistor is carried out in the usual manner.

[0062] The switching block 15 is designed to recognize the start of the respective switching phases 452, 454 in a received message 45 from bus 40 and then to switch the properties of the transmit / receive device 12. The switching block 15 can switch between the following operating modes of the transmit / receive device 12: a) First operating mode: Z_SL = transmit / receive characteristics for the arbitration phase 451, transmit module 121 in the transmit / receive device 12 generates dominant and recessive states on the bus 40, receive module 122 operates with a receive threshold T_a of typically about 0.7 V. c) Second operating mode: transmit / receive characteristics for the data phase 453 as receiver (receive node), transmit module 121 in the transmit / receive device 12 generates recessive states or is optionally switched off after the switching phase 452, since the transmit / receive device 12 is not a transmitter, but only acts as a receiver of the message 45 or a frame 450, receive module 122 operates with a receive threshold T_d of typically about 0.0 V.c) Third operating mode: Transmit / receive characteristics for the data phase 453 as transmitter (transmit node), transmit module 121 in the transmit / receive device 12 drives a 0 state or a 1 state depending on the TxD signal, since the transmit / receive device 12 acts as the sender of the message 45 or a frame 450, receive module 122 operates with a receive threshold T_d of typically about 0.0 V.

[0063] The RxD port configuration module 113 of the communication control unit 11 configures the RxD port according to the required communication direction using signals S1 and S2 at the input of the module 113, as described below. Signal S1 can be designated as RxD_out_ena, which either prevents the additional signal RxD_TC from being driven via the RxD port (first port operating mode) or enables the additional signal RxD_TC from being driven via the RxD port (second port operating mode). Signal S2 can be designated as RxD_out_val.Depending on the value of signal S2, the communication control unit 11 drives the RxD connection at the switching points between the two different communication phases to signal the operating mode to be set to the transmit / receive unit 12. This occurs, firstly, in the first switching phase 452, for switching between arbitration phase 451 and data phase 453, and secondly, in the second switching phase 454, for switching between data phase 453 and frame end phase 455. Optionally, depending on the value of signal S2, the communication control unit 11 can drive the RxD connection in a third operating mode, which can also be called "talk mode," in which internal communication between units 11 and 12 is possible.Otherwise, as is typical for CAN, the RxD connection is an input for the communication control unit 11, not an output as described previously, so the communication control unit 11 does not drive the RxD connection. The RxD connection can therefore be operated bidirectionally using the RxD connection configuration module 113 and the S1 and S2 signals. In other words, the RxD connection is a bidirectional connection.

[0064] For this purpose, the communication control unit 11 and the output driver 124 are designed such that the communication control unit 11 drives the RxD connection more strongly than the output driver 124 when driving it for signaling purposes. This prevents the value of the RxD line from being undefined if both the communication control unit 11 and the output driver 124 drive the RxD connection and the two signal sources overlap at the RxD connection. In such a case of overlap, the communication control unit 11 always prevails. Therefore, the value of the RxD line is always defined.

[0065] This allows the switching block 15 to provide the option of setting one of the three aforementioned operating modes in the transmit / receive unit 12, which are signaled via the RxD and TxD connections. An additional connection in the form of another pin on the transmit / receive unit 12, and therefore also on the communication control unit 11, is not required for this.

[0066] The switching block 15 is designed for this purpose according to Fig. 3 The switching block 15 is equipped with three inputs through which a signal RxD_TC, a signal TxD, and a signal S_SW are fed. The RxD_TC signal is based on a signal sent by the communication control unit 11 to the transmit / receive unit 12 via the RxD signal connection. With the RxD_TC signal, the communication control unit 11 signals to the transmit / receive unit 12 that the transmit / receive unit 12 should now switch to the operating mode for the data phase 453. With the TxD signal, the communication control unit 11 signals to the transmit / receive unit 12 which of the operating modes Z_F_RX or Z_F_TX the switch should be made. This is particularly useful when switching from the arbitration phase 451 to the data phase 453.At the end of data phase 453, the communication control unit 11 can use the signal RxD_TC to signal the switching of the transmit / receive unit 12 from either of the two operating modes of data phase 453 to the operating mode Z_SL for arbitration phase 451. Furthermore, any other information can be sent from the communication control unit 11 to the transmit / receive unit 12 using the signal RxD_TC, as previously mentioned.

[0067] According to Fig. 3 The transmit / receive unit 12 routes the RxD_TC signal from the RxD terminal via the driver 125 to the RxD_TC signal switching block 15. The S_SW signal, on the other hand, is generated from the signal received by bus 40. The RxD_TC signal is routed to the switching block 15 between the RxD signal terminal and the output of the receive signal driver 124. The S_SW signal is routed to the switching block 15 from the output of the receive module 122 and before the input of the receive signal driver 124.

[0068] When switching block 15 detects switching phase 452, the operating state of the transmit module 121 is set using the signal S_OP output from switching block 15, and the operating state of the receive module 122 is set using the signal S_OP, thereby switching the operating mode of the transmit / receive device 12. This is in relation to Fig. 4 bis Fig. 9 explained in more detail.

[0069] In operation of bus system 1, when the participant station 10 acts as a transmitter, the transmitter module 121 converts a transmission signal TxD from the communication control unit 11 into corresponding signals CAN_H and CAN_L for the bus wires 41, 42 and sends these signals CAN_H and CAN_L to bus 40, as shown in Fig. 4 The transition from arbitration phase 451 with switching phase 452 to data phase 453 is shown. This involves switching from a bit duration T_B1 of arbitration phase 451 to a shorter bit duration T_B2 of data phase 453. Although the signals CAN_H and CAN_L are mentioned here for the transmit / receive device 12, these are to be understood as signals CAN-XL_H and CAN-XL_L with respect to message 45. In data phase 453, these differ from the conventional signals CAN_H and CAN_L in at least one characteristic, particularly with regard to the formation of the bus states for the different data states of the signal TxD and / or with regard to the voltage or the physical layer and / or the bit rate. In the example of Fig. 4 In data phase 453, the signals CAN-XL_H and CAN-XL_L differ from the conventional signals CAN_H and CAN_L in phases 451 and 452 with regard to the formation of the bus states for the different data states of the signal TxD and with regard to the voltage or the physical layer and the bit rate.

[0070] As in Fig. 5 As shown, a differential signal VDIFF = CAN_H - CAN_L is generated as a result of the signals on bus 40. Except in an idle or standby state, the transceiver 12 with the receiver module 122 is always listening for data or message transmissions 45, 46 on bus 40 during normal operation, regardless of whether the receiving station 10 is the sender of message 45 or not. During the arbitration phase 451 and at the beginning of the switching phase 452, the receiver module 122 uses the receive threshold T_a. At the end of the switching phase 452 and in the data phase 453, the receiver module 122 uses only the receive threshold T_d, which is at 0V or between + / - 0.1V. The minimum value for a differential voltage of a bus state D0 in data phase 453, which is called VDIFF_D0_Min, lies in the lower range for the receive threshold T_d.The receiver module 122 generates a signal S_SW and passes this on to the communication control unit 11 as a digital receive signal RxD via the receive signal output driver 124, as shown in . Fig. 3 shown.

[0071] Fig. 6 This shows a portion of the transmitted signal TxD_T, which is sent, for example, from subscriber station 10 to bus 40. At the end of the arbitration phase 451, it is clear which of the subscriber stations 10 and 30 will act as transmitters and which will act only as receivers in the subsequent data phase 453. In this example, subscriber station 10 acts as both a transmitter and a receiver, while subscriber station 30 acts only as a receiver.

[0072] According to Fig. 8 The subscriber station 10, acting as transmitter and receiver, receives a signal with a predetermined delay time T_TLD, also known as Transmitter Loop Delay, and forms a digital received signal RxD_T from it with the receiver module 122 and the driver 124.

[0073] As in Fig. 4 bis Fig. 6 As shown, before the switching phase 452, the communication control unit 11 transmits an FDF bit and an XLF bit sequentially in the transmit signal TxD, each in the high state (first binary signal state). This is followed by a resXL bit, which is transmitted in the low state (second binary signal state), and then by an AL1 bit, which is also transmitted in the low state (second binary signal state). At the end of the arbitration phase 451, the communication control unit 11 switches from the bits of the arbitration phase 451 with bit time T_B1 to the shorter bits of the data phase 453 with bit time T_B2, as shown in Fig. 4 bis 7 shown. The communication control unit 11 signals the transmit / receive unit 12 in the switching phase 452 using the signal RxD_TC, which is shown in Fig. 7 As shown, and given a pulse duration T_B3, the transmitting / receiving device must switch its operating mode. In the example of Fig. 7 The pulse duration T_B3 is shorter than the bit time T_B2. Alternatively, the pulse duration T_B3 is longer than the bit time T_B2. The pulse duration T_B3 is shorter or shorter than the bit time T_B1. After the AL1 bit, bits DH1 and DL1 of data phase 453 follow, and then the user data.

[0074] According to Fig. 7 The transmit / receive device 12 of the subscriber station 10 thus sees a received signal RxD_T, which in the AL1 bit differs from the previously described course of the TxD_T signal from Fig. 6 , exhibits a high pulse AH_1. In other words, the communication control unit 11 sends a high pulse AH_1 (shown with a thick line) via the RxD port using signals S1 and S2 in Fig. 3 The high pulse AH_1 is sent during the AL1 bit and corresponds to the first binary signal state. The communication control unit 11 therefore only briefly overwrites the RxD signal.

[0075] Since the AL1 bit of the TxD_T signal from Fig. 6 When the AL1 bit is in the low state (second binary signal state), the RxD_T and TxD_T signals of the transmit / receive device 12 indicate that the transmit / receive device 12 is to switch from its first operating mode (Z_SL) to its third operating mode (Z_F_TX). This allows the transmit / receive device 12 to generate the bus signals CAN_H and CAN_L from the following bits of the transmit signal TxD. In the example of... Fig. 4 bis Fig. 7 The switching of the operating mode Z_SL of the transmit / receive device 12 with the switching block 15 on the falling edge of the pulse AH_1. The signaling with the signal S_OP to the transmit module 121 in Fig. 3 However, this only occurs from the next edge transition in the signal TxD_T. Thus, the transmitting module 121 only transmits with the new signal levels, i.e., the signal levels of the operating mode of data phase 453, from the beginning of data phase 453. In the third operating mode Z_F_TX, the subscriber station 10 acts as both sender and receiver of the message 45 or frame 450, as also from Fig. 6 und Fig. 7 visible.

[0076] Fig. 8 shows that the transmitting module of the subscriber station 30 sends a transmit signal TxD_R with the state High (first binary signal state) at the end of the arbitration phase 451, since the transmitting / receiving device 32 of the subscriber station 30 is only a receiver of the signal from Fig. 6 or the resulting signals from Fig. 4 und Fig. 5 Furthermore, the transmit / receive device 32 of the subscriber station 30 sees a received signal RxD_R according to Fig. 10, which in the AL1 bit, deviating from the previously described course of the TxD_T signal from Fig. 6 , exhibits a high pulse AH_1. In other words, the communication control unit 31 sends a high pulse AH_1 (shown with a thick line) via its RxD port using signals S1 and S2 in Fig. 3 The communication control unit 11 therefore only overrides the RxD signal briefly.

[0077] The high pulse AH_1 is sent during the AL1 bit, as with subscriber station 10, and corresponds to the first binary signal state. Since the AL1 bit of the TxD_R signal from Fig. 8When the AL1 bit is in the high state (first binary signal state), the RxD_R and TxD_R signals of the transmit / receive device 32 indicate that the transmit / receive device 12 is to switch from its first operating mode to its second operating mode (Z_F_RX). The RxD_TC signal causes the switching mode of the transmit / receive device 12 with the switching block 15 on the falling edge of pulse AH_1. In the second operating mode, the receiving station 30 acts only as a receiver of frame 450, meaning that the receiving station 30 has lost the preceding arbitration or currently has no message 45 to send.

[0078] The signaling from the communication control unit 11, 31 to the transmit / receive unit 12, 32 can thus be carried out such that the combination of the signals TxD, RxD in bit AL1 with only one pulse AH_1, however depending on the value of the signal at the TXD terminal of the transmit / receive unit 12, 32, indicates which operating mode the transmit / receive unit 12, 32 is to be switched to in the data phase 453. Afterwards, the transmission of the data of the data field 453 of a frame 450 can be carried out.

[0079] The receiver module 122 immediately switches its receive threshold T_a of the arbitration phase 451 to the receive threshold T_d of the data phase 453. This applies to the transmit / receive devices 32 and 12. If the transmit / receive device 12 is to be switched to the third operating mode, i.e., when the transmit / receive device 12 acts as the transmitter of the frame 450, the transmit / receive device 12 can only switch to the second operating mode at the next edge of the transmit signal TxD_T.

[0080] Switching the operating mode on the next edge of the transmit signal TxD or the signal S_SW has the advantage that each bit is assigned a differential voltage VDIFF on bus 40, since the switching of the operating mode or the states in the transmit / receive unit 12, 32 occurs at the bit boundary, i.e., on the next edge. This is because the AL1 bit is a dominant bit and is therefore encoded with VDIFF = +2V. The short bit that follows the AL1 bit is already transmitted in the second operating mode (Z_F_TX) and is encoded on the bus as VDIFF = -1V.

[0081] If, however, the switching in the transmit / receive unit 12, 32 is performed immediately, i.e., during the AL1 bit, the differential voltage VDIFF changes during the AL1 bit, and some receiving nodes might therefore detect additional edges. Since this disrupts the synchronization of the receiving stations 10, 20, 30, this is rather disadvantageous.

[0082] The following applies to the transition from data phase 453 to frame end phase 455. Here, too, the communication control unit 12, 32 signals its associated transmitter / receiver unit 12, 32 to switch the operating mode of the transmitter / receiver unit 12, 32, with the signaling also being effected by means of one or more pulses via the RxD signal. Evaluation of the transmitted signals TxD_T, TxD_R is not necessary here, since the transmitter / receiver unit 12, 32 must always be switched back to the first operating mode, regardless of the operating mode of the respective transmitter / receiver unit 12, 32. Furthermore, the transmitter / receiver unit 12, 32 can delay the switchover until it detects a bit boundary. The transmit / receive unit 12 in the transmitter detects the bit boundary at an edge on the TxD input pin.The transmit / receive device 12, 32 in the receiver, which is not a transmitter of the frame 450, detects the bit boundary on an edge on the CAN bus 40.

[0083] In the event that the signaling from the communication control unit 11, 31 to the associated transmit / receive unit 12, 32 is disrupted, the switching block 15, 35 does not recognize the aforementioned switching condition. To nevertheless be able to continue participating in the communication, the switching block 15 additionally uses a predetermined timeout as a switching condition. If the transmit / receive unit 12, 32 is in operating mode Z_F_TX and no edge transition occurs at the terminal or signal TxD for a preset duration T0, the switching block 15, 25 switches the transmit / receive unit 12, 32 to the first operating mode Z_SL. If the transmit / receive device 12, 32 is in operating mode Z_F_RX and no edge change occurs on the signal S_SW for a preset time period T0, the switching block 15, 25 switches the transmit / receive device 12, 32 to the first operating mode Z_SL.

[0084] Due to the previously described design of the subscriber station 10, no galvanic connection via an additional connection is required on the communication control unit 11 and the associated transceiver 12 for the communication control unit 11 to transmit the time of the operating mode switch. This means that block 15 advantageously does not require an additional connection that is not available on a standard transceiver 12 housing. Therefore, block 15 does not need to be redesigned with a larger and more expensive housing to provide an additional connection.

[0085] Furthermore, the operating mode switch block 15 eliminates the need for protocol controller functionality in the transmit / receive device 12. Such a protocol controller could, among other things, detect the switching phase 452 of message 45 and initiate the data phase 453 accordingly. However, since such an additional protocol controller would require considerable space in the transmit / receive device 12 or the ASIC, the operating mode switch block 15 significantly reduces resource requirements.

[0086] This means that connecting the operating mode switching block 15 with a conventional transmit / receive device offers a very simple and cost-effective solution to indicate to the transmit / receive device 12 that a switchover and which switchover between its different operating modes is to be carried out, namely in particular from the first operating mode to the second operating mode or from the first operating mode to the third operating mode or from the second operating mode to the first operating mode or any other switchover of operating modes.

[0087] The described design of the transmit / receive device(s) 12, 32 enables significantly higher data rates in data phase 452 than with CAN or CAN-FD. Furthermore, the data length in the data field of data phase 453 can be chosen arbitrarily, as previously described. This allows the advantages of CAN with regard to arbitration to be retained while still transmitting a larger amount of data in a shorter time than before, very reliably and therefore efficiently, i.e., without the need for data retransmission due to errors, as explained below.

[0088] Another advantage is that error frames are not required in bus system 1 when transmitting messages 45, although they can be used optionally. If error frames are not used, messages 45 are no longer destroyed, thus eliminating a reason for the need for duplicate message transmission. This increases the net data rate.

[0089] If the bus system is not a CAN bus system, the operating mode switching block 15, 35 can be designed to react to other switching signals. In this case, depending on the result of its evaluation, the operating mode switching block 15, 35 can switch the transmit module 121 and / or the receive module 122 into one of at least two different operating modes and switch at least one of the operating modes to another after a time period T0 preset in the operating mode switching block 15, 35 has elapsed.

[0090] According to a second embodiment, the operating mode switching signal RxD_TC has at least one pulse with a pulse duration T_B3 that is approximately equal to or shorter than the second bit time T_B2. This also allows for very fast, yet very reliable and therefore robust signaling of the switching process.

[0091] Otherwise, the bus system 1 in the second embodiment is constructed in the same way as previously described in relation to the first embodiment.

[0092] All previously described configurations of blocks 15 and 35, participant stations 10, 20, and 30, bus system 1, and the method implemented therein can be used individually or in any possible combination. In particular, all features of the previously described embodiments and / or their modifications can be combined as desired. Additionally or alternatively, the following modifications are particularly conceivable.

[0093] Although the invention has been previously described using the example of the CAN bus system, it can be used in any communication network and / or communication method that employs two different communication phases in which the bus states generated for these different communication phases differ. In particular, the invention is applicable to the development of other serial communication networks, such as Ethernet and / or 10Base-T1S Ethernet, fieldbus systems, etc.

[0094] The previously described bus system 1, according to the exemplary embodiments, is based on the CAN protocol. However, the bus system 1, according to the exemplary embodiments, can also be a different type of communication network in which data can be transmitted serially at two different bit rates. It is advantageous, but not a necessary requirement, that the bus system 1 ensures, at least for certain periods of time, exclusive, collision-free access to a common channel for each participating station 10, 20, 30.

[0095] The number and arrangement of participant stations 10, 20, 30 in the bus system 1 of the exemplary embodiments are arbitrary. In particular, participant station 20 can be omitted from bus system 1. It is possible that one or more of participant stations 10 or 30 are present in bus system 1. It is conceivable that all participant stations in bus system 1 are configured identically, i.e., that only participant station 10 or only participant station 30 is present.

Claims

1. Transmitting / receiving device (12; 32) for a subscriber station (10; 30) of a serial bus system (1), having a first connection for receiving a transmission signal (TxD; TxD_T; TxD_R) from a communication control device (11; 31), a transmitting module (121) for converting the transmission signal (TxD; TxD_T; TxD_R) into signals (CAN_H, CAN_L) for bus wires (41, 42) of a bus (40) of the bus system (1) and for sending the signals (CAN_H, CAN_L) to the bus (40), in which bus system (1) at least a first communication phase (451, 452, 454, 455) and a second communication phase (453) are used for exchanging messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1), the transmitting / receiving device (12; 32) needing to be switched to a first mode (Z_SL) for the first communication phase (451, 452, 454, 455), needing to be switched from the first mode (Z_SL) to a second or third mode (Z_F_RX, Z_F_TX) for the second communication phase (453), and needing to be switched from both the second and third modes (Z_F_RX, Z_F_TX) to the first mode (Z_SL) at the end of the second communication phase (453), a receiving module (122) for receiving a signal (VDIFF) from the bus (40), and the receiving module (122) being designed to use the signal (VDIFF) received from the bus (40) to generate a signal (S_SW) and to forward the latter as a digital received signal (RxD) to the communication control device (11; 31), a second connection for sending the digital received signal (RxD) to the communication control device (11; 31) and for receiving from the communication control device (11; 31) a mode changeover signal (RxD_TC) that has at least one pulse (AH_1) for signalling changeover of the mode of the transmitting / receiving device (12; 32), with the result that the transmitting / receiving device (12; 32) sees on the second connection a received signal (RxD_T, RxD_R) that, unlike the transmission signal (TxD_T; TxD_R), has the at least one pulse (AH_1) in a bit (AL1), and a mode changeover block (15; 35) for evaluating the mode changeover signal (RxD_TC) received on the second connection from the communication control device (11; 31), the mode changeover block (15; 35) being designed to switch reception thresholds (T_a; T_d) of the receiving module (122) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC), of the signal (S_SW) received from the bus (40) and of the transmission signal (TxD; TxD_T; TxD_R) in order to switch the transmitting / receiving device (12; 32) to the second mode (Z_F_RX), and the mode changeover block (15;35) being designed to switch the transmitting module (121) and reception thresholds (T_a; T_d) of the receiving module (122) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC), of the signal (S_SW) received from the bus (40) and of the transmission signal (TxD; TxD_T; TxD_R) in order to switch the transmitting / receiving device (12; 32) from the first mode (Z_SL) to the third mode (Z_F_TX).

2. Transmitting / receiving device (12; 32) according to Claim 1, the mode changeover signal (RxD_TC) received on the second connection being a pulse (AH_1) having a value that is the inverse of a value of the digital received signal (RxD; RxD_T; RxD_R), the mode changeover block (15; 35) being designed to switch the reception thresholds (T_a; T_d) of the receiving module (122) in order to switch the transmitting / receiving device (12; 32) from the first mode (Z_SL) to the second mode (Z_F_RX) when the changeover signal (RxD_TC) has the pulse (AH_1) and the value of the transmission signal (TxD_R) corresponds to the value of the pulse (AH_1), and the mode changeover block (15;35) being designed to switch the transmitting module (121) and the reception thresholds (T_a; T_d) of the receiving module (122) in order to switch the transmitting / receiving device (12; 32) from the first mode (Z_SL) to the third mode (Z_F_TX) when the changeover signal (RxD_TC) has the pulse (AH_1) and the value of the transmission signal (TxD_T) is the inverse of the value of the pulse (AH_1).

3. Transmitting / receiving device (12; 32) according to Claim 2, the transmitting / receiving device (12; 32) not being the sender of the message (45) in the second communication phase (453) in the second mode (Z_F_RX), and the transmitting / receiving device (12; 32) being the sender of the message (45) in the second communication phase (453) in the third mode (Z_F_TX).

4. Transmitting / receiving device (12; 32) according to one of the preceding claims, the mode changeover block (15; 35) being designed to perform the changeover of the mode, at least for the changeover from the second communication phase (453) to the first communication phase (454, 455, 451, 452), when an edge in the received signal (S_SW) that is output by the receiving module (122) occurs between different bus states and the transmitting / receiving device (12; 32) is not the sender of the message (45).

5. Transmitting / receiving device (12; 32) according to one of the preceding claims, the mode changeover block (15; 35) being designed to shut down the transmitting module (121) in a mode of the second communication phase (453) in which the transmitting / receiving device (12; 32) is not the sender of the message (45).

6. Transmitting / receiving device (12; 32) according to one of Claims 1 to 4, the mode changeover block (15; 35) being designed to perform the changeover of the mode, at least for the changeover from the first communication phase (454, 455, 451, 452) to the second communication phase (453), when the transmitting / receiving device (12; 32) is the sender of the message (45) in the second communication phase (453) and an edge in the transmission signal (TxD; TxD_T) occurs between different bus states.

7. Transmitting / receiving device (12; 32) according to one of the preceding claims, the mode changeover block (15;35) being designed to switch off the transmitting module (121) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC), of the signal (S_SW) received from the bus (40) and of the transmission signal (TxD; TxD_T; TxD_R) in order to switch the transmitting / receiving device (12; 32) to the second mode (Z_F_RX; Z_F_TX), and / or the mode changeover block (15;35) being designed to switch the transmitting module (121) and reception thresholds (T_a; T_d) of the receiving module (122) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC) and of the signal (S_SW) received from the bus (40) in order to switch the transmitting / receiving device (12; 32) to the first mode (Z_SL) at the end of the second communication phase (453).

8. Transmitting / receiving device (12; 32) according to one of the preceding claims, the transmitting module (121) being designed to drive bits of the signals onto the bus (40) with a first bit time (T_B1) in the first communication phase (451, 452, 454, 455), which first bit time is longer by at least a factor of 10 than a second bit time (T_B2) of bits that the transmitting module (121) drives onto the bus (40) in the second communication phase (453).

9. Transmitting / receiving device (12; 32) according to Claim 8, the mode changeover signal (RxD_TC) via the second connection, for signalling that changeover of the mode needs to be performed, having a pulse with a pulse period (T_B3) that is shorter than the first bit time (T_B1) and is longer than the second bit time (T_B2), or the mode changeover signal (RxD_TC) via the second connection having at least one pulse with a pulse period (T_B3) that is approximately equal to the second bit time (T_B2) or is shorter than the second bit time (T_B2).

10. Transmitting / receiving device (12; 32) according to one of the preceding claims, the signal (S_SW) received from the bus (40) in the first communication phase (451, 452, 454, 455) being generated by means of a different physical layer than the signal (S_SW) received from the bus (40) in the second communication phase (453).

11. Communication control device (11; 31) for a subscriber station (10; 30) of a serial bus system (1), having a communication control module (111) for generating a transmission signal (TxD; TxD_T; TxD_R) for controlling communication between the subscriber station (10; 30) and at least one other subscriber station (10; 20; 30) of the bus system (1), in which bus system (1) at least a first communication phase (451, 452, 454) and a second communication phase (453) are used for exchanging messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1), a first connection for sending the transmission signal (TxD; TxD_T; TxD_R) to a transmitting / receiving device (12; 32), which, to send the transmission signal (TxD) to a bus (40) of the bus system (1), is designed in such a way that the transmitting / receiving device (12; 32) needs to be switched to a first mode (Z_SL) for the first communication phase (451, 452, 454, 455) and needs to be switched to a second or third mode (Z_F_RX, Z_F_TX) for the second communication phase (453), a second connection for receiving a digital received signal (RxD; RxD_T; RxD_R) from the transmitting / receiving device (12; 32), the communication control device (11; 31) being designed to generate a mode changeover signal (RxD_TC) that has at least one pulse (AH_1) for signaling changeover of the mode of the transmitting / receiving device (12;32) and that indicates to the transmitting / receiving device (12; 32) that it is necessary to switch from the current mode to a different mode of the first to third modes, and that implements internal communication between the communication control module (111) and the transmitting / receiving device (12; 32), and the communication control module (111) being designed to send the mode changeover signal (RxD_TC) to the transmitting / receiving device (12; 32) via the second connection and, in order to change over the transmitting / receiving device (12; 32) from the first mode (Z_SL) to the second or third mode (Z_F_RX, Z_F_TX), to signal to the transmitting / receiving device (32; 32), at the same time as the transmission signal (TxD; TxD_T; TxD_R) sent on the first connection, to which of the modes (Z_F_RX, Z_F_TX) the transmitting / receiving device (12; 12) needs to be switched.

12. Communication control device (11; 31) according to Claim 11, the mode changeover signal (RxD_TC) via the second connection, for signalling that changeover of the mode of the transmitting / receiving device (12; 32) needs to be performed, having a pulse with a pulse period (T_B3) that is shorter than a first bit time (T_B1) with which bits of the signals are driven onto the bus (40) in the first communication phase (451) and longer than the second bit time (T_B2), with which bits of the signals are driven onto the bus (40) in the second communication phase (453), or the mode changeover signal (RxD_TC) via the second connection having at least one pulse with a pulse period (T_B3) that is approximately equal to the second bit time (T_B2) or is shorter than the second bit time (T_B2).

13. Communication control device (11; 31) according to Claim 11 or 12, the first communication phase (451, 452, 454, 455) involving negotiating 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 (453).

14. Bus system (1) having a bus (40), and at least two subscriber stations (10; 20;30) 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 has a transmitting / receiving device (12; 32) according to one of Claims 1 to 10 and a communication control device (11; 31) according to one of Claims 11 to 13.

15. Method for communication in a serial bus system (1), the method being carried out by means of a transmitting / receiving device for a subscriber station (10; 30) of a bus system (1) in which at least a first communication phase (451, 452, 454, 455) and a second communication phase (453) are used for exchanging messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1), the transmitting / receiving device (12; 32) needing to be switched to a first mode (Z_SL) for the first communication phase (451, 452, 454, 455), needing to be switched from the first mode (Z_SL) to a second or third mode (Z_F_RX, Z_F_TX) for the second communication phase (453), and needing to be switched from both the second and third modes (Z_F_RX, Z_F_TX) to the first mode (Z_SL) at the end of the second communication phase (453), the subscriber station (10; 30) having a transmitting module (121), a receiving module (122), a mode changeover block (15; 35), a first connection for receiving a transmission signal (TxD; TxD_T; TxD_R) from the communication control device (11; 31), and a second connection, and the method comprising the steps of receiving, by means of the receiving module (122), a signal (VDIFF) from the bus (40) of the bus system (1), generating, by means of the receiving module (122), a signal (S_SW) from the signal (VDIFF) received from the bus (40) and outputting the signal (S_SW) as a digital received signal (RxD) on the second connection, evaluating, by means of the mode changeover block (15; 35), a mode changeover signal (RxD_TC) that is received on the second connection from the communication control device (11; 31) and has at least one pulse (AH_1) for signaling changeover of the mode of the transmitting / receiving device (12; 32), switching, at the end of the first communication phase (454, 455, 451, 452), by means of the mode changeover block (15; 35), reception thresholds (T_a; T_d) of the receiving module (122) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC), of the signal (S_SW) received from the bus (40) and of the transmission signal (TxD; TxD_T; TxD_R) received on the first connection in order to switch the transmitting / receiving device (12; 32) from the first mode (Z_SL) to the second mode (Z_F_RX), or switching, at the end of the first communication phase (454, 455, 451, 452), by means of the mode changeover block (15; 35), the transmitting module (121) and reception thresholds (T_a; T_d) of the receiving module (122) on the basis of a result of the evaluation of the mode changeover signal (RxD_TC), of the signal (S_SW) received from the bus (40) and of the transmission signal (TxD; TxD_T; TxD_R) in order to switch the transmitting / receiving device (12; 32) to the third mode (Z_F_TX).