GB2607254A - Transmitting/receiving device for a subscriber station of a serial bus system, and method for communication in a serial bus system - Google Patents

Abstract

The invention relates to a transmitting/receiving device (12;32) for a subscriber station (10; 30) of a serial bus system (1), and to a method for communication in a serial bus system (1). The transmitting/receiving device (12; 32) comprises: a first connection for receiving a transmission signal (TxD) from a communication control device (11; 31); a transmitter (121) for transmitting the transmission signal (TxD) to a bus (40) of the bus system (1), in which bus system (1) at least one first communication phase (451, 452, 454, 454) and a second communication phase (453) are used to exchange messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1); a receiver (122) for receiving the signal from the bus (40), wherein the receiver (122) is designed to generate a digital receiver signal (RxD) from the signal received from the bus (40); a second connection for transmitting the digital receiver signal (RxD; RxD_T; RxD_R) to the communication control device (11; 31) and for receiving an operating mode switching signal (RxD_TC) from the communication control device (11; 31); and an operating mode switching block (15; 35 150) for evaluating the operation mode switching signal (RxD_TC) received by the communication device on the second connection, wherein the operating mode switching block (15; 35; 150) is designed to switch the transmitter (121) and/or the receiver (122) into one of three different operating modes according to a result of the evaluation, and the operating mode switching block (15; 35; 150) is designed to time delay a switching of the operating mode of the second communication phase (453) to the operating mode of the first communication phase (454, 455, 451, 452) up to a bit limit of a switchover phase (454) between the communication phases. Fig. 3 Nothing to translate into English

Description

Description

Transmitting/receiving device for a subscriber station of a serial bus system and method for communication in a serial bus system

Technical field

The present invention relates to a transmitting/receiving unit for a subscriber station of a serial bus system and a method for communication in a serial bus system operating at a high data rate and with high error robustness.

Prior art

A bus system in which data are transmitted as messages in the standard IS011898-1:2015 as a CAN protocol specification with CAN FD is often used for communication between sensors and control devices, for example in vehicles. The messages are transmitted as analogue signals between the bus subscribers of the bus system, such as sensor, control device, encoder, etc. Each bus subscriber of the bus system is connected to the bus by means of a transmitting/receiving unit. In the transmitting/receiving unit, at least one reception comparator is provided, which receives the analogue signals from the bus and converts them into a digital signal. The content of the digital signal can be interpreted by a protocol controller. In addition, the protocol controller can create a signal for transmission on the bus and transmit it to the bus by means of the transmitting/receiving unit so that information can be exchanged between the bus subscribers.

In order to be able to transmit data via the bus at a higher bit rate than in the case of CAN, an option for switching to a higher bit rate within a message was created in the CAN ED message format as well as in the CAN XL message format. In such technologies, the maximum possible data rate is increased by using higher clocking in the range of the data fields in comparison to CAN. In the case of CAN FD frames or CAN ED messages, the maximum possible data rate is increased beyond a value of 1 Mbit/s. In addition, the payload data length is extended from 8 to up to 64 bytes. The same applies to CAN XL, in which the speed of the data transmission is to be increased into the range of, for example, 10 Base-T1S Ethernet and the payload data length of up to 64 bytes previously achieved with CAN FD is to be greater. As a result, the robustness of the CAN-or CAN FD-based communication network can advantageously be maintained. -2 -

In the course of the specification of the analogue serial data transmission on the CAN bus line, transmission levels and reception thresholds for the at least one input comparator of the transmitting/receiving unit (transceiver) of each subscriber station have now been defined for CAN XL. The transmission levels and reception thresholds have been optimized to be as flexible as possible in the design of the bus line topology and differ in the various modes of operation of the transmitting/receiving unit (transceiver).

It is disadvantageous that the two logical bit levels on the CAN bus line are not always clearly detected when the receiving transmitting/receiving unit is set to different reception thresholds than transmission levels on the bus. This may occur in particular when a transmitting/receiving unit (transceiver) is woken up from an idle state and attempts to reintegrate into the ongoing communications on the bus. In order to enable such 1.0 an integration of a CAN subscriber station, in which the CAN subscriber station does not yet know which mode of operation is the correct one for the transmitting/receiving unit, a third reception threshold T_OoB (threshold out-of-bounds), which has a value of -0.4 V, for example, was added for the at least one input comparator.

However, the problem is that the reception threshold T_OoB may interfere with synchronization of the 1 5 subscriber stations. The reason why is that when switching back from the data phase to the arbitration phase, the reception threshold T_OoB shifts bit flanks at the port of the transmitting/receiving unit for an RxD signal formed from the signal received from the bus.

Disclosure of the invention

It is therefore the object of the present invention to provide a transmitting/receiving unit for a subscriber station of a serial bus system and a method for communication in a serial bus system, which solve the problems mentioned above. In particular, a transmitting/receiving unit 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 integration of a CAN subscriber station into the ongoing communications is improved.

The task is achieved by a transmitting/receiving unit for a subscriber station of a serial bus system with the features of claim 1. The transmitting/receiving unit has a first port for receiving a transmit signal from a communication control unit, a transmitting module for transmitting the transmit signal to a bus of the bus system, in which bus system at least a first communication phase and a second communication phase are used to exchange messages between subscriber stations of the bus system, a receiving module for receiving the signal from the bus, wherein the receiving module is configured to generate a digital receive signal from the signal received from the bus, a second port for transmitting the digital receive signal to the -3 -communication control unit for receiving a mode switching signal from the communication control unit, and a mode switching block for evaluating the mode switching signal received at the second port from the communication control unit, wherein the mode switching block is configured to switch the transmitting module and/or the receiving module to one of three different modes of operation depending on a result of the evaluation, and wherein the mode switching block is configured to delay switching of the mode of operation of the second communication phase to the mode of operation of the first communication phase up to a bit limit of a switching phase between the communication phases.

With the transmitting/receiving unit, it is possible to prevent a "false positive" in the CAN idle detection. As a result, integration of a subscriber station into the ongoing communications on the bus can be enabled. In 1.0 addition, the synchronization of the transmitting/receiving unit and thus of the superordinate subscriber station (CAN node) is still enabled or maintained.

In addition, by means of the transmitting/receiving unit, arbitration known from CAN can be maintained in one of the communication phases and the transmission rate can once again still be significantly increased compared to CAN or CAN FD. This can be achieved by using two communication phases at different bit rates and by reliably identifying the start of the second communication phase, in which the payload data are transmitted at a higher bit rate than in the arbitration, for the transmitting/receiving unit. The transmitting/receiving unit can therefore reliably switch from a first communication phase to the second communication phase or vice versa. As a result, a significant increase in the bit rate and thus in the transmission speed from transmitter to receiver can be realized. In this case, a large error robustness is however ensured at the same time.

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

Advantageous further configurations of the transmitting/receiving unit are specified in the dependent claims.

The mode switching block may be configured to perform the mode switching during the switching from the second communication phase to the first communication phase when a flank between different bus states occurs in the receive signal emitted by the receiving module and the transmitting/receiving unit is not the transmitter of the message.

The mode switching block may be configured to switch off the transmitting module in a mode of operation -4 -of the second communication phase in which the transmitting/receiving unit is not the transmitter of the message.

The mode switching block may be configured to perform the mode switching during the switching from the second communication phase to the first communication phase when the transmitting/receiving unit is the transmitter of the message in the second communication phase and a flank between different bus states occurs in the transmit signal.

The transmitting module may be configured to drive bits of the signals to the bus in the first communication phase at a first bit time that is greater by at least the factor 10 than a second bit time of bits that the transmitting module drives to the bus in the second communication phase. In this case, the mode switching signal via the second port for signalling the mode switching may have at least one pulse with a pulse duration that is approximately equal to the second bit time or shorter than the second bit time.

The communication control unit may be configured to transmit an identifier with a predetermined value as the mode switching signal to the receiving module at the port for the digital receive signal when switching from the first communication phase to the second communication phase is to take place.

For example, the identifier is a bit with a predetermined value or pulse pattern, or the identifier is a predetermined bit pattern.

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

It is conceivable that in the first communication phase, it is negotiated which of the subscriber stations of the bus system gains at least temporary exclusive, collision-free access to the bus in the subsequent second communication phase.

The transmitting/receiving unit described above and the communication control unit described above may be part of a subscriber station of a bus system that also comprises a bus and at least two subscriber stations that are connected to one another via the bus in such a way that they can communicate serially with one another. In this case, at least one of the at least two subscriber stations comprises a transmitting/receiving unit described above.

The aforementioned object is also achieved by a method of communication in a serial bus system according -5 -to claim 13. The method is carried out by means of a transmitting/receiving unit of a subscriber station for a bus system, in which at least a first communication phase and a second communication phase are used to exchange messages between subscriber stations of the bus system, wherein the subscriber station comprises a transmitting module, a receiving module, a mode switching block, a first port, and a second port, and wherein the method comprises the steps of: receiving, by means of the receiving module, a signal from the bus of the bus system; generating, by means of the receiving module, a digital receive signal from the signal received from the bus, and emitting the digital receive signal at the second port; evaluating, by means of the mode switching block, a mode switching signal received at the second port from the communication control unit; and switching, by means of the mode switching block, the transmitting module and/or the receiving module to one of three different modes of operation depending on a result of the evaluation, wherein the mode switching block delays switching of the mode of operation of the second communication phase to the mode of operation of the first communication phase up to a bit limit of a switching phase between the communication phases.

The method offers the same advantages as mentioned above with respect to the transmitting/receiving unit 1.5 and/or the communication control unit.

Further possible implementations of the invention also include not explicitly mentioned combinations of features or embodiments described above or below with respect to the exemplary embodiments. In this respect, the person skilled in the art also adds individual aspects as improvements or additions to the respective basic form of the invention.

Drawings The invention is described in more detail below with reference to the appended drawing and using exemplary embodiments. Shown are Fig. 1 a simplified block diagram of a bus system according to a first exemplary embodiment; Fig. 2 a diagram illustrating the structure of messages that may be transmitted from subscriber stations of the bus system according to the first exemplary embodiment; Fig. 3 a simplified schematic block diagram of a subscriber station of the bus system according to the first exemplary embodiment; Fig. 4 an electrical diagram of a mode switching block for switching the mode of operation of a -6 -transmitting/receiving unit of the subscriber station of Fig. 3; Fig. 5 to Fig. 9 a time curve of signals according to the first exemplary embodiment for a time phase, in which a first mode of operation of the transmitting/receiving unit, which is switched on in the arbitration phase (first communication phase), is switched to one of two modes of operation of the transmitting/receiving unit, in which the transmitting/receiving unit can be switched to a data phase as a second communication phase; Fig. 10 to Fig. 15 a time curve of signals according to the first exemplary embodiment for a time phase, in which the mode of operation of the transmitting/receiving unit for the second communication phase, the mode of operation of the transmitting/receiving unit for the data phase, is switched back to the first mode of operation, which is the mode of operation of the transmitting/receiving unit for the arbitration phase; Fig. 15 to Fig. 17 a time curve of signals at the subscriber station of Fig. 3 when the subscriber station attempts to integrate into ongoing communications on the bus; and Fig. 18 an electrical diagram of a mode switching block for switching the mode of operation of a transmitting/receiving unit of the subscriber station of Fig. 3 according to a second exemplary embodiment.

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

Description of the exemplary embodiments

As an example, Fig. 1 shows a bus system 1, which is in particular configured to be fundamental for a CAN bus system, a CAN FD bus system, a CAN FD successor bus system, and/or modifications thereof, as described below. The bus system 1 may be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in a hospital, etc. In Fig. 1, the bus system 1 has a plurality of subscriber 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 41,42 can also be called CAN_H and CAN_L and are used for electrical signal transmission after coupling-in the dominant level or generating recessive levels for a signal in the transmit state. Via the bus 40, messages 45,46 in the form of signals can be transmitted serially between the individual subscriber stations 10, 20, 30. The subscriber stations 10, 20, 30 are, for example, control devices, sensors, indicator devices, etc. of a motor vehicle.

As shown in Fig. 1, the subscriber station 10 has a communication control unit 11, a transmitting/receiving -7 -unit 12, and a switching block 15. In contrast, the subscriber station 20 has a communication control unit 21 and a transmitting/receiving unit 22. The subscriber station 30 has a communication control unit 31, a transmitting/receiving unit 32, and a switching block 35. The transmitting/receiving unit 12, 22, 32 of the subscriber stations 10, 20, 30 are each connected directly to the bus 40, even if this is not illustrated in Fig. 1.

In each subscriber station 10, 20, 30, the messages 45,46 are exchanged encoded in the form of frames bit by bit between the respective communication control unit 11, 21, 31 and the associated transmitting/receiving units 12, 22, 32 via a TXD line and an RXD line. This is described in more detail below.

The communication control units 11, 21, 31 are each used to control communications 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 connected to the bus 40.

The communication control units 11, 31 create and read first messages 45, which are, for example, modified CAN messages 45, which are hereinafter also referred to as CAN XL messages 45. Here, the modified CAN messages 45 or CAN XL messages 45 are constructed based on a CAN FD successor format, which is described in more detail with reference to Fig. 2. The communication control units 11, 31 may also be designed to, as needed, provide a CAN XL message 45 or a CAN FD message 46 for the transmitting/receiving units 12, 32, or receive it from the latter. The communication control units 11, 31 thus create and read a first message 45 or second message 46, wherein the first and second messages 45, 46 differ by their data transmission standard, namely in this case CAN XL or CAN FD.

The communication control unit 21 may be designed 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 second messages 46, for example classical CAN messages or CAN FD messages 46. A number of 0 to 64 data bytes may be included in the CAN FD messages 46 and are even transmitted at a significantly faster data rate than in the case of a classical CAN message. In the latter case, the communication control unit 21 is designed like a conventional CAN FD controller.

The transmitting/receiving units 12, 32 may be designed as a CAN XL transceiver except for the differences described in more detail below.

The transmitting/receiving units 12, 32 may additionally or alternatively be designed like a conventional CAN FD transceiver. The transmitting/receiving unit 22 may be designed like a conventional CAN transceiver or -8 -CAN FD transceiver.

With the two subscriber stations 10, 30, formation and then transmission of messages 45 with the CAN XL format as well as reception of such messages 45 can be realized.

Fig. 2 shows a CAN XL frame 450 for the message 45 as transmitted from the transmitting/receiving unit 12 or the transmitting/receiving unit 32. The CAN XL frame 450 is divided into different communication phases 451 to 455 for the CAN communication on the bus 40, namely an arbitration phase 451, a first switching phase 452 that is at the end of the arbitration phase 451, a data phase 453, a second switching phase 454 that is at the end of the data phase 453, and a frame end phase 455.

In the arbitration phase 451, a bit is, for example, transmitted at the beginning, which bit is also called the SOF bit and indicates the start of frame. In the arbitration phase 451, an identifier with, for example, 11 bits is also transmitted to identify the transmitter of the message 45. During arbitration, with the aid of the identifier, it is bit by bit negotiated between the subscriber stations 10, 20, 30 which subscriber station 10, 20, 30 would like to transmit the message 45, 46 with the highest priority and therefore gain exclusive access to the bus 40 of the bus system 1 for the near future for transmitting in the switching phase 452 and the subsequent data phase 453.

In the present exemplary embodiment, the switching from the arbitration phase 451 to the data phase 453 is prepared in the first switching phase 452. In the process, protocol format information contained in at least one bit is transmitted and is suitable to distinguish CAN XL frames from CAN frames or CAN FD frames. The switching phase 452 may have a bit AU which has the bit duration T B1 of a bit of the arbitration phase 451 and is transmitted with the physical layer of the arbitration phase 451. The physical layer corresponds to the bit transmission layer or layer 1 of the known 051 model (open systems interconnection model). In addition, a 12-bit long data length code, for example, may be transmitted, which may then, for example, assume values from 1 to 4096, in particular up to 2048, or another value with the increment of 1, or may alternatively assume values from 0 to 4095 or higher. The data length code may alternatively comprise less or more bits so that the value range and the increment may assume different values.

In the data phase 453, the payload data of the CAN XL frame 450 or of the message 45 are transmitted, which may also be referred to as the data field of the message 45. The payload data may have data corresponding to the value range of the data length code, for example with a number of up to 4096 bytes or a greater number of bytes or any other amount of data. For example, at the end of the data phase 453, a checksum field may contain a checksum of the data of the data phase 453, including the stuff bits inserted each time as -9 -an inverse bit by the transmitter of the message 45 after a predetermined number of identical bits, in particular 10 identical bits. In particular, the checksum is a frame checksum F_CRC, with which all bits of the frame 450 up to the checksum field are secured. Thereafter, an FCP field with a predetermined value, for example 1100, may follow.

In the present exemplary embodiment, the switching from the data phase 453 to the frame end phase 455 is prepared in the second switching phase 454. In the process, protocol format information contained in at least one bit is transmitted and is suitable to implement the switching. The switching phase 454 may have a bit AH1 which has the bit duration T_B1 of a bit of the arbitration phase 451 but is transmitted with the physical layer of the data phase 453.

In the frame end phase 455, after two bits AL2, AH2, at least one acknowledge bit ACK may be contained in an end field in the frame end phase 455. Thereafter, a sequence of 11 identical bits may follow, which indicate the end of the CAN XL frame 450. With the at least one acknowledge bit ACK, it can be communicated whether a receiver has detected an error in the received CAN XL frame 450 or the message 45 or not.

At least in the arbitration phase 451 and the frame end phase 455, a physical layer like in the case of CAN and CAN FD is used. Additionally, in the first switching phase 452, a physical layer like in the case of CAN and CAN FD may be used at least sometimes, i.e., at the beginning. Additionally, in the second switching phase 454, a physical layer like in the case of CAN and CAN FD can be used at least sometimes, i.e., at the end.

An important point during the phases 451, 455, at the beginning of the phase 452 and at the end of the phase 454 is that the known CSMA/CR method is used, which allows simultaneous access of the subscriber stations 10, 20, 30 to the bus 40 without the higher priority message 45,46 being destroyed. As a result, additional bus subscriber stations 10, 20, 30 can be added to the bus system 1 relatively easily, which is very advantageous.

The CSMA/CR method results in the need to have so-called recessive states on bus 40, which states can be overwritten by other subscriber stations 10, 20, 30 with dominant states on bus 40.

The arbitration at the beginning of a frame 450 or of the message 45,46 and the acknowledgement in the frame end phase 455 of the frame 450 or of the message 45,46 is only possible if the bit time is significantly more than twice as long as the signal transit time between any two subscriber stations 10, 20, 30 of the bus system 1. The bit rate in the arbitration phase 451, the frame end phase 455, and at least sometimes in the switching phases 452, 454 is therefore selected to be slower than in the data phase 453 of the frame 450. In -10 -particular, the bit rate in the phases 451, 452, 454, 455 is selected to be 500 kbit/s, which results in a bit time of approximately 2 is, whereas the bit rate in the data phase 453 is selected to be 5 to 10 Mbit/s or more, which results in a bit time of approximately 0.1 ps and shorter. The bit time of the signal in the other communication phases 451, 452, 454, 455 is thus greater by at least the factor 10 than the bit time of the signal in the data phase 453.

A transmitter of the message 45, for example the subscriber station 10, does not begin to transmit bits of the switching phase 452 and the subsequent data phase 453 to the bus 40 until the subscriber station 10 as the transmitter has won the arbitration and the subscriber station 10 as transmitter thus has exclusive access to the bus 40 of the bus system 1 for transmitting. The transmitter may either switch to the faster bit rate and/or 1.0 the other physical layer after a portion of the switching phase 452 or may not switch to the faster bit rate and/or the other physical layer until the first bit, i.e., the start, of the subsequent data phase 453.

In general, the following deviating properties can in particular be realized in the bus system with CAN XL in comparison to CAN or CAN FD: a) assumption and, if applicable, adaptation of proven properties responsible for the robustness and ease of use 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 4 Kbytes or to any other value.

Fig. 3 shows the fundamental structure of the subscriber station 10 with the communication control unit 11, the transmitting/receiving unit 12, and the switching block 15. The subscriber station 30 is constructed in a similar manner, as shown in Fig. 3, except that block 35 is provided separately from the communication control unit 31 and the transmitting/receiving unit 32. The subscriber station 30 and the block 35 are therefore not described separately. The functions of the switching block 15 described below are identical to those of the switching block 35.

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

However, not shown in Fig. 3 is a system ASIC (ASIC = application-specific integrated circuit), which may alternatively be a system basis chip (SBC), on which a plurality of functions necessary for an electronic assembly of the subscriber station 10 are combined. The transmitting/receiving unit 12 and a power supply unit (not shown), which supplies electrical power to the transmitting/receiving unit 12, may be installed in the system ASIC, among other things. The power supply unit usually supplies a voltage CAN_Supply of 5 V. However, the power supply unit may supply a different voltage with a different value and/or be configured as a power source as needed.

According to Fig. 3, the transmitting/receiving unit 12 also has a transmitting module 121, a receiving module 122, a driver 123 for the transmit signal TxD, a receive signal output driver 124, and a driver 125 emitting a signal RxD_TC to the switching block 15. The switching block 15 forms, from the signal RxD_TC and a signal 1.0 S_SW, which is the output signal of the receiving module 122, an operating state switching signal S_OP for switching the transmitting module 121 and/or the receiving module 122. In addition, the switching block 15 forms, from the signal S_OP and the signals TxD, S_SW, an operating state switching signal S_OPT for switching reception thresholds of the receiving module 122. For example, the switching signal S_OP may contain in one bit the switching signal for the transmitting module 121 and the receiving module 122.

1.5 Alternatively, the switching signal S_OP may be a two-bit wide signal in order to separately control the transmitting module 121 and the receiving module 122, for example by providing the first bit for switching the transmitting module 121 and the second bit for switching the receiving module 122. Of course, any alternative options of the configuration of the switching signal S_OP are conceivable. The transmitting module 121 is also referred to as transmitter. The receiving module 122 is also referred to as receiver.

The switching block 15 can be configured as a switching block that in particular comprises at least one flipflop.

This is described in more detail below with reference to Fig. 4 to Fig. 14.

Although reference is always made below to the transmitting/receiving unit 12, it is alternatively possible to provide the receiving module 122 in a separate unit external to the transmitting module 121. The transmitting module 121 and the receiving module 122 may be constructed as in a conventional transmitting/receiving unit 22. In particular, the transmitting module 121 may comprise at least one operational amplifier and/or a transistor. In particular, the receiving module 122 may comprise at least one operational amplifier and/or a transistor.

As shown in Fig. 3, the transmitting/receiving unit 12 is connected to the bus 40, more specifically its first bus wire 41 for CAN_H and its second bus wire 42 for CAN_L. In the transmitting/receiving unit 12, the first and second bus wires 41,42 are connected to the transmitting module 121 and to the receiving module 122. The voltage supply for the power supply unit for supplying electrical power to the first and second bus wires 41, -12 - 42 takes place as usual. In addition, the connection to ground or CAN_GND is realized as usual. The same applies to the termination of the first and second bus wires 41,42 with a terminating resistor.

The switching block 15 is configured to detect the start of the respective switching phases 452, 454 in a received message 45 from bus 40 and to then switch the properties of the transmitting/receiving unit 12. In the process, the switching block 15 can switch between the following modes of operation of the transmitting/receiving unit 12: a) first mode of operation: transmit/receive properties for the arbitration phase 451, b) second mode of operation: transmit/receive properties for the data phase 453 as transmitter (transmitting node), transmitting/receiving unit 12 acts as transmitter and thus also as receiver of the message 45 or of a 1.0 frame 450, c) third mode of operation: transmit/receive properties for the data phase 453 as receiver (receiving node), transmitting/receiving unit 12 is not a transmitter but acts only as receiver of the message 45 or of a frame 450.

The RxD port configuration module 113 configures the RxD port according to the required communication 1 5 direction using signals Si, S2 at its input, as described below. The signal Si may be referred to as RxD_out_ena, which does not allow the additional signal RxD_TC to be driven via the RxD port (first port mode) or allows the additional signal RxD_TC to be driven via the RxD port (second port mode). The signal S2 may be referred to as RxD_out_val. According to the value of the signal S2, the communication control unit 11 drives the RxD port at the switching times between the two different communication phases in order to signal the mode of operation to be set to the transmitting/receiving unit 12, i.e., on the one hand, in the first switching phase 452 to switch between the arbitration phase 451 and the data phase 453 and, on the other hand, in the second switching phase 454 to switch between the data phase 453 and the frame end phase 455. Optionally, according to the value of the signal 52, the communication control unit 11 can drive the RxD port to a third port mode, which can also be called "talk mode", in which internal communications between the units 11, 12 is possible. Otherwise, as in particular usual in the case of CAN, the RxD port is an input, i.e., no output, as previously described, for the communication control unit 11 so that the communication control unit 11 does not drive the RxD port. The RxD port can thus be operated bi-directionally with the aid of the RxD port configuration module 113 and the signals Si, 52. In other words, the RxD port is a bi-directional port.

For this purpose, the communication control unit 11 and the output driver 124 are configured in such a way that when driving for the purpose of signalling, the communication control unit 11 drives the RxD port more strongly than the output driver 124. This prevents the value of the RxD line from being indeterminate if both -13 -the communication control unit 11 and the output driver 124 drive the RxD port and superimposition of the two signal sources occurs at the RxD port. In the event of such a superimposition of the two signal sources at the RxD port, the communication control unit 11 thus always prevails. As a result, the value of the RxD line is always determined.

The switching block 15 can thus provide the possibility of signalling, via the RxD port, a setting of one of the aforementioned three modes of operation in the transmitting/receiving unit 12, which form different operating states of the transmitting/receiving unit 12. An additional port on the transmitting/receiving unit 12 and thus also on the communication control unit 11 is not required for this purpose.

For this purpose, according to Fig. 3, the switching block 15 is provided with the three inputs via which a signal RxD_TC, the signal TxD, and the signal S_SW are fed into the switching block 15. The signal RxD_TC is based on a signal transmitted from the communication control unit 11 via the port for the RxD signal to the transmitting/receiving unit 12. With the signal RxD_TC, the communication control unit 11 signals to the transmitting/receiving unit 12 on the one hand that the transmitting/receiving unit 12 now has to perform the switching to the mode of operation for the data phase 453. At the end of the data phase 453, the communication control unit 11 may use the signal RxD_TC to perform the switching of the transmitting/receiving unit 12 from the mode of operation of the data phase 453 to the mode of operation for the arbitration phase 451. In addition, with the signal RxD_TC, any other information may be transmitted from the communication control unit 11 to the transmitting/receiving unit 12, as mentioned above.

According to Fig. 3, the transmitting/receiving unit 12 guides the signal RxD_TC from the RxD port via the driver 125 to the port of the switching block 15 for the signal RxD_TC. In contrast, the signal S_SW is generated from the signal received from the bus 40. The signal RxD_TC is routed between the port for the RxD signal and the output of the receive signal driver 124 to the switching block 15. The signal S_SW is routed from the output of the receiving module 122 and prior to the input of the receive signal driver 124 to the switching block 15.

According to a particular example shown in Fig. 4, the switching block 15 has two D-flipflops 151, 152, into which the signal RxD_TC is entered as a clock signal. The two D-flipflops 151, 152 respond to rising clock flanks of the clock signal, i.e., the signal RxD_TC. A high state or a first binary signal state is also applied with the signal S_FI to the input of the D-flipflop 151. In addition, the inverted signal S_SW is entered as a reset into the D-flipflops 151, 152. The signal S_SW is routed via an inverter 155 prior to the entry into D-flipflops 151, 152. D-flipflops 151, 152 are connected to logic gates 156, 157, namely an AND gate 156 and an OR gate 157. The output of the OR gate 157 is supplied to a D-flipflop 158 as a clock signal, into which a time-out -14 -signal S_TO is also fed as a reset, which indicates the expiration of a predetermined time duration TO. The signal S_TO becomes active if no flanks are detected on the bus 40 for a predetermined time duration TO, for example 11 bit times. The D-flipflop 158 responds to rising clock flanks. In addition, an inverter 159 is connected between the D-flipflop 158 and an input of the AND gate 156. In the particular example of Fig. 4, while the signal S_SW is high, the third D-flipflop 158 is switched from 0 to 1 by two falling flanks of the signal RxD_TC. While the signal S_SW is high, if the flip-flop 158 is 1, it is switched from 1 to 0 by a falling flank of the signal RxD_TC. If the signal S_SW is low, the two D-flipflops 151, 152 are reset and do not respond to rising flanks of the signal RxD_TC.

With the aid of a block 160, the transmitting/receiving unit 12 can first store the switching signal RxD_TC, 1.0 which contains at least one high pulse driven by the communication control unit 11, during the transition from the data phase 453 to the frame end phase 455. This is described in more detail below with reference to Fig. 5 to Fig. 14.

The previously described switching conditions can of course be defined differently, for example rising flanks on the signal RxD_TC while the signal S_SW is low. In addition, other levels and/or other numbers of flanks 1 5 are possible with other circuits in the switching block 15.

In the particular example of Fig. 4, the D-flipflop 158 drives the binary operating state switching signal S_OP. If the switching signal S_OP is to be two bits wide or if more than two operating states are to be represented, additional D-flipflops with different switching conditions than previously described are required.

If the switching block 15 detects the switching phase 452, the operating state of the transmitting module 121 and/or of the receiving module 122 and thus the mode of operation of the transmitting/receiving unit 12 is switched with the signal 5_0P emitted from the switching block 15. This is explained in more detail with reference to Fig. 5 to Fig. 9.

During operation of the bus system 1, when the subscriber station 10 acts as transmitter, the transmitting module 121 converts a transmit signal TxD of the communication control unit 11 into corresponding signals CAN_H and CAN J. for the bus wires 41,42 and transmits these signals CAN_H and CAN J.. to the bus 40 as shown in Fig. 5 for the transition from the arbitration phase 451 with the switching phase 452 to the data phase 453. In the process, a bit duration T_B1 of the arbitration phase 451 is switched to a shorter bit duration LK of the data phase 453. Even if the signals CAN_H and CAN_L are mentioned here for the transmitting/receiving unit 12, they are to be understood with respect to the message 45 as signals CAN-XL_H and CAN-XL_L, which in the data phase 453 deviate from the conventional signals CAN_H and CAN J. in -15 -at least one characteristic, in particular with respect to the formation of the bus states for the different data states of the signal TxD and/or with respect to the voltage or the physical layer and/or the bit rate. In the example of Fig. 5, the signals CAN-XL_H and CAN-XL_L in the data phase 453 deviate with respect to the formation of the bus states for the different data states of the signal TxD and with respect to the voltage or the physical layer and the bit rate from the conventional signals CAN_H and CAN_L in the phases 451, 452.

As shown in Fig. 6, a differential signal VDIFF = CAN_H -CAN_L forms as a result of the signals on the bus 40. With the exception of an idle or standby state, the transmitting/receiving unit 12 always listens with the receiving module 122 during normal operation for a transmission of data or messages 45, 46 on the bus 40, regardless of whether or not the subscriber station 10 is the transmitter of the message 45. Here, in the 1.0 arbitration phase 451 and at the start of the switching phase 452, the receiving module 122 uses a reception threshold T_a. At the end of the switching phase 452 and in the data phase 453, the receiving module 122 uses only one reception threshold T_d, which is between 0 V or between +/-0.1 V. The minimum value for a differential voltage of a bus state DO in the data phase 453, referred to as VDIFF_DO_Min, is in the lower range for the reception threshold T_a. The receiving module 122 forms a signal S_SW and passes it as a digital 1.5 receive signal RxD via the receive signal output driver 124 to the communication control unit 11, as shown in Fig. 3. If the transmitting/receiving unit 12 is switched to the mode of operation for the arbitration phase 451, the unit 12 cannot reliably detect the "0" bits of the data phase 453 because the current switching threshold or reception threshold T_a is in its lower tolerance range and could thus be below VDIFF_DO_Min.

Fig. 7 shows a portion of the transmit signal TxD transmitted, for example, from the subscriber station 10 to the bus 40. With a delay time duration T_TLD set during operation, which is also referred to as transmitter loop delay, the subscriber station 10 as transmitter receives a signal and forms therefrom, by means of the receiving module 122 and the driver 124, a digital receive signal RxD_T as shown in Fig. 8. The delay time duration T_TLD depends on temperature, operating voltage, and production tolerances and is usually specified in a tolerance range indicated in the data sheet of the transmitting/receiving unit 12. Ideally, there is no delay time duration T_TLD.

According to Fig. 5 to Fig. 7, prior to the switching phase 452, the communication control unit 11 sequentially transmits in the transmit signal TxD an FDF bit and an XLF bit, each at the high state (first binary signal state). Thereafter follows an resXL bit transmitted at the low state (second binary signal state) and followed by an AL1 bit transmitted at the low state (second binary signal state). Thereafter, at the end of the arbitration phase 451, due to a signal RxD_TC shown in Fig. 8 and having a pulse duration T_B3, switching takes place from the bits of the arbitration phase 451 with bit time T_B1 to the bit levels and switching threshold(s) of the data phase 453 and also with bit time LK, as shown in Figs. 5 to 9. The pulse duration T_B3 is -16 -approximately equal to or less or shorter than the bit time T_132. In particular, the pulse duration T_I33 is equal to the bit time T_B2. The pulse duration T_B3 is less or shorter than the bit time T_B1. The AL1 bit is followed by bits DH1, DL1 of the data phase 453 and then the payload data. The signal RxD_TC only switches the analogue components 121,122 of the transmitting/receiving unit 12. The lengths of the bit times T_131, T_132 are only switched within the digital communication control unit 11.

According to Fig. 9, the subscriber station 30, which is, for example, only the receiver of the signal from the bus 40, receives the signal from the bus 40 with an additional delay time duration T_BLD, also referred to as the bus line delay. The subscriber station 30 forms therefrom a digital receive signal RxD_R, as shown in Fig. 9. The receive signal RxD_R is thus additionally delayed by the delay time duration T_BLD in comparison to 1.0 the receive signal RxD_T.

According to Fig. 8, the transmitting/receiving unit 12 of subscriber station 10 thus sees a receive signal RxD_T, which has two high pulses AL_2 in the AU bit, which has the second binary signal state (low) in deviation from the previously described curve of the TxD signal of Fig. 7. In other words, the communication control unit 11 transmits via the RxD port a signal RxD_TC, in which an identifier in the form of two pulses AL_2 with the first binary signal state (high), i.e., with the inverse signal state, is transmitted in the AL bit. The transmitting/receiving unit 12 is thereby signalled to switch from its first mode of operation to its second mode of operation in order to generate the bus signal CAN_H, CAN_L from the following bits of the transmit signal TxD. The signal RxD_TC brings about the switching by means of the switching block 15 at the flank S_TD. In the second mode of operation, the subscriber station 10 acts as transmitter and as receiver of the message 45 or of the frame 450.

According to Fig. 9, the transmitting/receiving unit 32 of subscriber station 30 in contrast sees a receive signal RxD_R, which has one high pulse AL_1 in the ALl bit in deviation from the previously described curve of the TxD signal of Fig. 7. In other words, the communication control unit 31 transmits via its RxD port a signal RxD_TC, in which an identifier in the form of one pulse AL_1 with the first binary signal state (high), i.e., with the inverse signal state, is transmitted in the AL bit. The transmitting/receiving unit 32 is thereby signalled to switch from its first mode of operation to its third mode of operation. The signal RxD_TC brings about the switching by means of the switching block 15 at the flank S_RD. In the third mode of operation, the subscriber station 30 only acts as receiver of the frame 450, i.e., the subscriber station 30 has lost the preceding arbitration or currently does not have a message 45 to transmit.

The signalling may thus take place in such a way that a sequence of two high pulses AL_2 indicates the transition from the arbitration phase 451 (first mode of operation) to the data phase 452 as transmitter -17 - (second mode of operation) as shown in Fig. 8, and that a high pulse AL_1 indicates the transition from the arbitration phase 451 (first mode of operation) to the data phase 452 as receiver (third mode of operation), as shown in Fig. 9. Thereafter, the transmission of the data of the data field 453 of a frame 450 may be carried out.

During the transition of the mode of operation of the transmitting/receiving unit 12 from the first mode of operation (arbitration) to the second or third mode of operation, the time delay of the block 160 is set to the value of zero. The receiving module 122 thus immediately switches its reception threshold T_a of the arbitration phase 451 to the reception threshold T_d of the data phase 453. If the transmitting/receiving unit 12 is to be switched to the second mode of operation, i.e., when the transmitting/receiving unit 12 acts as 1.0 transmitter of the frame 450, the transmitting module 121 switches when the transmit signal Tx() switches to low (second signal state). Of course, other switching conditions are likewise conceivable.

As can be seen in Fig. 10 to Fig. 14, the transmitting/receiving unit 12 proceeds as follows during the transition from the data phase 453 to the frame end phase 455. With the aid of block 160, the transmitting/receiving unit 12 first stores the switching signal RxD_TC, which contains a low pulse driven by the communication control unit 12, as shown in Fig. 13. The block 160 then waits for a flank in the TxD signal according to Fig. 12 and then simultaneously switches its transmitting module 122 as well as the reception threshold of its receiving module from the reception threshold T_d of the data phase 453 to the reception threshold T_a for arbitration, i.e., the switching thresholds of its reception comparator. Additionally, the transmitting/receiving unit 12 switches on a reception threshold T_OoB (threshold out-of-bounds) for its reception comparator in the receiving module.

In contrast, the transmitting/receiving unit 32, which in the example shown is only a receiver of the frame 450, proceeds during the transition from the data phase 453 as shown in Fig. 11 and Fig. 14. The transmitting/receiving unit 32 waits for a flank S_TH on the bus 40, i.e., a flank of the signal S_SW, and only then switches the reception threshold of its receiving module from the reception threshold T_d of the data phase 453 to the reception threshold T_a for arbitration, i.e., the switching thresholds of its reception comparator. Additionally, the transmitting/receiving unit 32 switches on a reception threshold T_OoB (threshold out-of-bounds) for its reception comparator in the receiving module.

In other words, if the communication control unit 12,32 signals its associated transmitting/receiving unit 12, 32 to switch the mode of operation of the transmitting/receiving unit 12, 32, the transmitting/receiving unit 12, 32 delays switching until the transmitting/receiving unit 12, 32 detects a bit limit. The transmitting/receiving unit 12 in the transmitter detects the bit limit at a flank on the TxD input pin. The -18 -transmitting/receiving unit 12, 32 in the receiver, which is not a transmitter of the frame 450, detects the bit limit at a flank on the CAN bus 40.

This prevents the reception threshold T_OoB from disrupting the switching back of the transmitting/receiving unit 12 from the data phase 453 to the mode of operation of the arbitration phase 455, 451 by shifting the second flank of the AH1 bit at the RxD port. As a result, the synchronization of the subscriber stations 10, 20, 30 of the bus system 1 is not disrupted, which would otherwise be shifted by shifting the second flank of the AH1 bit at the RxD port.

The reception threshold T_OoB can thus be used during the integration of a subscriber station 10, 20, 30 into ongoing communications, as shown in Fig. 15 to Fig. 17. To this end, the subscriber station 10, 20, 30 looks for an uninterrupted sequence of 11 recessive bits, i.e., RxD = 1 or RxD_R = 1 or RxD_T = 1. Thereafter, the bus is detected as idle, i.e., in the idle state. This sequence of 11 recessive bits occurs between the dominant ACK bit of the one CAN frame 450 and the start bit SOF of the next CAN frame 450, or even if no frames 450 are being transmitted.

In the example of Fig. 15 to Fig. 17, communications on the bus 40 changes to the data phase 453 after the transmission of phases 451, 452. The subscriber station, which has been turned on, initially acts only as receiver and, in the process, generates a receive signal RxD_R as signal RxD, as shown in Fig. 17. For example, the subscriber station is the subscriber station 10. At the subscriber station 10, after switching on, the transmitting/receiving unit 12 is thus initially switched to the mode of operation for the arbitration phase 451. In the process, the reception thresholds T_a, T_OoB at the receiving module 122 are switched on, as illustrated in Fig. 16. The reception threshold T_OoB (threshold out-of-bounds) has become necessary because the reception threshold T_a of the arbitration phase 451 cannot reliably detect the logical '0 bits in the data phase 453. The reason why is that the reception threshold T_a is in the range of 0.5 V to 0.9 V, as specified in ISO 11898-2, according to manufacturing tolerances, temperature, and operating voltage. If the differential voltage VDIFF is higher, RxD = '0' = dominant. If the differential voltage VDIFF is lower, RxD = '1' = recessive. If the differential voltage VDIFF is in the specified range, RxD is indeterminate. A logical '0' should be transmitted as VDIFF = 1 V in the data phase 453. If this voltage is attenuated via the bus line to VDIFF = 0.8 V at the receiving subscriber stations (receiving nodes), this voltage VDIFF cannot be reliably detected with the reception threshold T_a.

According to Fig. 17, the subscriber station 10 forms the receive signal RxD_R from the signals received from the bus 40 according to Fig. 15 and Fig. 16 due to the reception thresholds T_a and T_OoB. For example, states DA_R whose voltage values U for the differential voltage VDIFF = CAN_H -CAN_L are not above the -19 -upper limit of the tolerance range defined for the reception threshold T_a are detected as recessive. In contrast, states D_D whose differential voltage is below the reception threshold T_OoB are detected as dominant. This also applies to the state D_D present at the time t1. The value for the threshold T_a is in the range of 0.5 V to 0.9 V due to the tolerances described above.

Thus, the reception threshold T_OoB causes the '1' bits in the data phase 453 to be emitted as '0' bits and thus compensates for undetected '0' bits when their differential voltage VDIFF is attenuated into the uncertain range of T_a. That is to say, the reception threshold T_OoB prevents such a subscriber station from mistakenly detecting a sequence of data bits as the idle state of the bus 40 and therefore assuming that the CAN bus 40 is free, and therefore starting its own frame, which disrupts the frame already transmitted.

1 0 Due to the previously described configuration of the subscriber station 10, no galvanic connection through a respective additional port to the communication control unit 11 and the transmitting/receiving unit 12 connected thereto is required so that the communication control unit 11 can transmit the time of the bit-level switching and switching-threshold switching or other data to the transmitting/receiving unit 12. This means that the block 15 advantageously does not require an additional port, which is not available on a standard housing of the transmitting/receiving unit 12. The block 15 thus does not require a change to another larger and costly housing in order to provide an additional port.

In addition, the mode switching block 15 makes it possible for the transmitting/receiving unit 12 to not require protocol controller functionality. Such a protocol controller could, among other things, detect the switching phase 452 of the message 45 and, depending thereon, initiate the data phase 453. However, since such an additional protocol controller would require considerable area in the transmitting/receiving unit 12 or the ASIC, the mode switching block 15 brings about a significant reduction in the need for resources.

As a result, the connection of the mode switching block 15 to a conventional transmitting/receiving unit provides a very inexpensive and cost-efficient solution in order to identify to the transmitting/receiving unit 12 that a switching and which switching between its different modes of operation is to be performed, namely, in particular, from the first mode of operation to the second mode of operation, or from the first mode of operation to the third mode of operation, or from the second mode of operation to the first mode of operation, or another mode switching.

The described configuration of the transmitting/receiving unit(s) 12, 32 can achieve far higher data rates in the data phase 452 than are achieved with CAN or CAN FD. In addition, the data length in the data field of the data phase 453 can be selected as desired, as previously described. As a result, the advantages of CAN -20 -with respect to arbitration can be maintained and a greater amount of data can still be transmitted in a very secure and thus effective manner in less time than before, i.e., without the need to repeat the data due to an error, as explained below.

Another advantage is that error frames in the transmission of messages 45 in the bus system 1 are not needed but can optionally be used. If error frames are not used, messages 45 are no longer destroyed, eliminating one reason for the need to transmit messages twice. This increases the net data rate.

If the bus system is not a CAN bus system, the mode switching block 15,35 may be configured to respond to other switching signals. In that case, the mode switching block 15, 35 may switch the transmitting module 121 and/or the receiving module 122 to one of at least two different modes of operation depending on a result of its evaluation and switch at least one of the modes of operation to another one of the modes of operation after expiration of a time duration TO preset at the mode switching block 15, 35.

Fig. 18 shows a variant for a switching block 150, which can be used according to a second exemplary embodiment at a subscriber station 10 instead of the switching block 15.

In contrast to the preceding exemplary embodiment, the switching block 150 uses the signal S_OP, instead of the signal RxD_TC, as input. The advantages of the preceding exemplary embodiment can be achieved in this manner as well.

Otherwise, the bus system 1 in the second exemplary embodiment is constructed in the same manner as described above with respect to the first exemplary embodiment.

All of the above-described configurations of blocks 15, 35, 150 of the subscriber stations 10, 20, 30 of the bus system 1 and the method carried out therein may be used individually or in all possible combinations. In particular, all features of the exemplary embodiments described above and/or their modifications may be combined as desired. In addition or alternatively, the following modifications are in particular conceivable.

Although the invention is described above using the example of the CAN bus system, the invention may be used in any communication network and/or communication method in which two different communication phases are used, in which the bus states generated for the different communication phases differ. In particular, the invention can be used in developments of other serial communication networks, such as Ethernet and/or 10 Base-T1S Ethernet, fieldbus systems, etc. -21 - The above-described bus system 1 according to the exemplary embodiments is described using a bus system based on the CAN protocol. However, the bus system 1 according to the exemplary embodiments may also be another type of communication network, in which data can be transmitted serially at two different bit rates. It is advantageous but not necessarily a prerequisite, for the bus system 1 to ensure exclusive, collision-free access of one subscriber station 10, 20, 30 to a common channel at least for certain periods of time.

The number and arrangement of the subscriber stations 10, 20, 30 in the bus system 1 of the exemplary embodiments is arbitrary. In particular, the subscriber station 20 in the bus system 1 may be omitted. It is possible that one or more of the subscriber stations 10 or 30 may be present in the bus system 1. It is conceivable that all subscriber stations in the bus system 1 are configured the same, i.e., only subscriber 1.0 stations 10 or only subscriber stations 30 are present.

Claims (13)

1. -21 -Claims 1) Transmitting/receiving unit (12; 32) for a subscriber station (10; 30) of a serial bus system (1), comprising a first port for receiving a transmit signal (TxD) from a communication control unit (11; 31), a transmitting module (121) for transmitting the transmit signal (TxD) to a bus (40) of the bus system (1), in which bus system (1) at least a first communication phase (451, 452, 454, 455) and a second communication phase (453) are used to exchange messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1), a receiving module (122) for receiving the signal from the bus (40), wherein the receiving module (122) is configured to generate a digital receive signal (RxD; RxD_T; RxD_R) from the signal received from the bus (40), a second port for transmitting the digital receive signal (RxD; RxD_T; RxD_R) to the communication control unit (11; 31) and for receiving a mode switching signal (RxD_TC) from the communication control unit (11; 31), and a mode switching block (15; 35; 150) for evaluating the mode switching signal (RxD_TC) received at the second port from the communication control unit (11; 31), wherein the mode switching block (15; 35; 150) is configured to switch the transmitting module (121) and/or the receiving module (122) to one of three different modes of operation depending on a result of the evaluation, and wherein the mode switching block (15; 35; 150) is configured to delay switching of the mode of operation of the second communication phase (453) to the mode of operation of the first communication phase (454, 455, 451, 452) up to a bit limit of a switching phase (454) between the communication phases.
2. 2) Transmitting/receiving unit (12; 32) according to claim 1, wherein the mode switching block (15; 35) is configured to perform the mode switching during the switching from the second communication phase (453) to the first communication phase (454, 455, 451, 452) when a flank between different bus states occurs in the receive signal (SSW) emitted by the receiving module (122) and the transmitting/receiving unit (12; 32) is not the transmitter of the message (45).
3. 3) Transmitting/receiving unit (12; 32) according to claim 1 or 2, wherein the mode switching block (15; 35) is configured to switch off the transmitting module (121) in a mode of operation of the second communication phase (453) in which the transmitting/receiving unit (12; 32) is not the transmitter of the message (45).
4. -22 - 4) Transmitting/receiving unit (12; 32) according to claim 1 or 2, wherein the mode switching block (15; 35) is configured to perform the mode switching during the switching from the second communication phase (453) to the first communication phase (454, 455, 451, 452) when the transmitting/receiving unit (12; 32) is the transmitter of the message (45) in the second communication phase (453) and a flank between different bus states occurs in the transmit signal (TxD).
5. 5) Transmitting/receiving unit (12; 32) according to any one of the preceding claims, wherein the transmitting module (121) is configured to drive bits of the signals to the bus (40) in the first communication phase (451) at a first bit time (T_B1) that is greater by at least the factor 10 than a second bit time (T_B2) of bits that the transmitting module (121) drives to the bus (40) in the second communication phase (453).
6. 6) Transmitting/receiving unit (12; 32) according to claim 5, wherein the mode switching signal (RxD_TC) via the second port for signalling the mode switching has at least one pulse having a pulse duration (T_B3) that is approximately equal to the second bit time (T_B2) or shorter than the second bit time (T_B2).
7. 7) Transmitting/receiving unit (12; 32) according to any one of the preceding claims, wherein the communication control unit (11; 31) is configured to transmit an identifier (AL_1; AL_2) with a predetermined value as the mode switching signal (RxD_TC) to the receiving module (122) at the port for the digital receive signal (RxD) when switching from the first communication phase (451, 452) to 2 0 the second communication phase (453) is to take place.
8. 8) Transmitting/receiving unit (12; 32) according to claim 7, wherein the identifier (AH_2; AH_3) is a bit having a predetermined value or pulse pattern.
9. 9) Transmitting/receiving unit (12; 32) according to claim 7, wherein the identifier (AH_2; AH_3) is a predetermined bit pattern.
10. 10) Transmitting/receiving unit (12; 32) according to any one of the preceding claims, wherein the signal received from the bus (40) in the first communication phase (451, 452, 454, 455) is generated with a different physical layer than the signal received from the bus (40) in the second communication phase (453).
11. 11) Transmitting/receiving unit (12; 32) according to any one of the preceding claims, wherein in the first -23 -communication phase (451, 452, 454, 455), it is negotiated which of the subscriber stations (10, 20, 30) of the bus system (1) gains at least temporary exclusive, collision-free access to the bus (40) in the subsequent second communication phase (453).
12. 12) Bus system (1) comprising 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 of which at least one subscriber station (10; 30) has a transmitting/receiving unit (12; 32) according to any one of claims 1 to 11.
13. 13) Method for communication in a serial bus system (1), wherein the method is carried out by means of a transmitting/receiving unit 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 to exchange messages (45; 46) between subscriber stations (10, 20, 30) of the bus system (1), wherein the subscriber station (10; 30) has a transmitting module (121), a receiving module (122), a mode switching block (15; 35), a first port, and a second port, and wherein the method comprises the steps of: receiving, by means of the receiving module (122), a signal from the bus (40) of the bus system (1), generating, by means of the receiving module (122), from the signal received from the bus (40), a digital receive signal (RxD; RxD_T; RxD_R) and emitting the digital receive signal (RxD; RxD_T; RxD_R) at the second port, evaluating, by means of the mode switching block (15; 35; 150), a mode switching signal (RxD_TC) received at the second port from the communication control unit (11; 31), and switching, by means of the mode switching block (15; 35), the transmitting module (121) and/or the receiving module (122) to one of three different modes of operation depending on a result of the evaluation, wherein the mode switching block (15; 35; 150) delays switching of the mode of operation of the second communication phase (453) to the mode of operation of the first communication phase (454, 455, 451, 452) up to a bit limit of a switching phase (454) between the communication phases.