CN110301115B

CN110301115B - Subscriber station for a bus system and method for data transmission in a bus system

Info

Publication number: CN110301115B
Application number: CN201780086378.XA
Authority: CN
Inventors: S.维森迈尔
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-12-14
Filing date: 2017-12-06
Publication date: 2021-12-21
Anticipated expiration: 2037-12-06
Also published as: KR20190103202A; CN110301115A; DE102016224961A1; EP3556058A1; WO2018108666A1

Abstract

A subscriber station (10) for a bus system (1; 2) and a method for data transmission in a bus system (1; 2) are provided. The user station (10) comprises a transmitting/receiving device (12) for transmitting messages (45; 46; 47) to other user stations (20; 30) of the bus system (1; 2) and/or for receiving messages (45; 46; 47) of other user stations (20; 30) of the bus system (1; 2) via the bus (40), wherein the transmitting/receiving device (12) is designed to: the differential voltage is reduced from a predetermined first voltage value for data transmission in a first time period to a predetermined second voltage value for data transmission in a second time period or is increased again from the predetermined second voltage value to the predetermined first voltage value, and the decision threshold (125, 126) for the bits of the message (45; 46; 47) is reduced from a predetermined first threshold value for data transmission in the first time period to a predetermined second threshold value for data transmission in the second time period or is increased again from the predetermined second threshold value to the predetermined first threshold value, and the subscriber station (10) is designed such that: the message (45; 47) is transmitted or received at a higher data transmission rate during the second time period than during the first time period.

Description

Subscriber station for a bus system and method for data transmission in a bus system

Technical Field

The invention relates to a subscriber station for a bus system and to a method for data transmission in a bus system, wherein a protocol for CAN or CAN FD is implemented at a lower voltage than is usual.

Background

For example, a CAN network is provided in a vehicle, in which messages are transmitted by means of the CAN and/or CAN FD protocol, as described in ISO-CD 11898-1, which is currently the CAN protocol specification, as CAN FD.

In the case of CAN, the data transmission rate cannot be increased further in many cases, since otherwise the voltage edges must be selected so steeply that more electromagnetic radiation than is permissible is generated. In the early days, only a single long CAN bus was available, which already connected all the control devices in the vehicle. Today, there are many shorter CAN buses due to the large number of users. Short cable lengths result in better signal-to-noise ratios.

Increasing communication over the CAN bus also requires increased data transfer rates beyond CAN FD.

Thus, what applicants consider is: instead of the CAN bus systems known to date, bus systems are used in which a lower voltage (low voltage) is used than the high voltage (high voltage) of 5V or 3.3V, which is conventionally used in digital systems. Such a System having a lower Voltage is known as LVDS (Low Voltage Digital System).

However, there are problems in that: the existing bus system is not compatible with LVDS subscriber stations based on an LVDS system. LV messages of LVDS subscriber stations are corrupted by subscriber stations in conventional subscriber stations. Thus, in the existing standard CAN system, all existing subscriber stations have to be retrofitted to the LVDS system. This is expensive and costly.

Disclosure of Invention

It is therefore an object of the present invention to provide a subscriber station for a bus system and a method for data transmission in a bus system, which subscriber station and method solve the problems mentioned above. In particular, a control device for a bus system and a method for data transmission in a bus system should be provided, wherein the data transmission rate on the bus can be increased further than in previous solutions, in order to accelerate the error-free communication via the bus in this way.

This object is achieved by a subscriber station for a bus system having the features of claim 1. The subscriber station comprises a transmitting/receiving device for transmitting messages to and/or receiving messages from other subscriber stations of the bus system via the bus, wherein the transmitting/receiving device is designed to: the differential voltage is reduced from a predetermined first voltage value for data transmission in a first time period to a predetermined second voltage value for data transmission in a second time period or is increased again from the predetermined second voltage value to the predetermined first voltage value, and the decision threshold for the bits of the message received in the second time period is reduced from a predetermined first threshold value for data transmission in the first time period to a predetermined second threshold value for data transmission in the second time period or is increased again from the predetermined second threshold value to the predetermined first threshold value, and the subscriber station is designed to: the message is transmitted at a higher data transmission rate during the second time period than during the first time period.

The data transmission rate CAN be increased by a factor of four with this subscriber station compared to a conventional CAN or CAN FD.

Another advantage is that: LV communications performed by the subscriber station, which are operated at a lower voltage (low voltage) than the high voltage (high voltage) of 5V or 3.3V which is conventionally used in digital systems, do not interfere with standard CAN or standard CAN FD communications on the bus. The LVCAN subscriber station generates a differential voltage during data transmission that is smaller than the usual differential voltage. The differential voltages are so small that they cannot be detected by standard CAN subscriber stations, since they are below the decision threshold of 1V, i.e. for example 0.5V or even negative.

Advantageously, the subscriber station is designed such that standard CAN users tolerate LV differential voltage variations performed by the described subscriber station and do not send error messages. Thus, a plurality of LV-CAN subscriber stations CAN communicate without interference. However, the subscriber station described above is designed such that it CAN be changed to a standard protocol if necessary and CAN then likewise exchange information with a standard CAN subscriber station.

The method implemented by the subscriber station described is therefore completely compatible with the CAN bus systems described to date. Thus, standard CAN subscriber stations or standard CAN FD subscriber stations CAN be gradually replaced in the bus by LV-CAN subscribers.

Further advantageous embodiments of the subscriber station are specified in the dependent claims.

According to one embodiment, the transmitting/receiving device has a connection and is designed to: the differential voltage and the decision threshold are reduced or increased depending on the signal at the connection. Additionally or alternatively, the transmission/reception device may be designed to: the content of the message is analyzed and the differential voltage and the decision threshold are lowered or raised depending on the content of the message.

According to one embodiment, the transmitting/receiving device has a first connection and is designed to: generating a differential voltage having a predetermined first voltage value for data transmission from a signal at the first connection; the transmitting/receiving device has a second connection for receiving bits with a decision threshold having a predetermined first threshold value; the transmitting/receiving device furthermore has a third connection and is designed to: generating a differential voltage having a predetermined second voltage value for data transmission as a function of the signal at the third connection; and the transmitting/receiving device has a fourth connection for receiving bits with a decision threshold having a predetermined second threshold value.

According to one embodiment, the subscriber station also has a communication control device which is designed to: transmitting a message with the insertion of a filler bit at a position in which a filler bit is expected when a subscriber station of the bus system is synchronized during a second time period, and/or wherein the communication control device or the transmitting/receiving device is designed to: the filler bits are created at such differential voltage levels and data transfer rates during the first time period. Additionally or alternatively, the communication control device or the transmitting/receiving device may be designed to: in addition to the dominant padding bits, the recessive padding bits are created directly in order.

The first time period is preferably a time period which determines which user stations are at least temporarily given exclusive, collision-free access to the bus or to a common channel of the bus. The second time period is preferably a time period in which the subscriber station has exclusive, collision-free access to the bus or to a common channel of the bus.

It is conceivable that: the level of the differential voltage has a value in the range of-1V and 3V on average. Additionally or alternatively, the differential voltage may have a value of U at 0.2V ≦ U_DA value in the range of 1V or less.

According to one embodiment, the transmission/reception device can be designed to: the LV transmission is modulated in parallel onto the transmission at a predetermined first current value. In addition or alternatively, the subscriber station can have an error counter which is designed to count how many times a transmission attempt is interrupted, and wherein the transmitting/receiving device is designed to switch to a transmitting operation, wherein the differential voltage is switched to a predetermined first voltage type, in order to transmit a message only at the original level and the original data transmission rate when the counter state of the error counter exceeds a predetermined value.

The bus system may be a CAN bus system or a CAN FD bus system. Additionally or alternatively, it is possible that: at least one reflection reducing unit is arranged in the transmitting/receiving device, and the reflection reducing unit is connected between two bus cores of the bus so as to reduce reflection in the bus system.

The previously described subscriber stations may be part of a bus system which further comprises a bus by means of which at least two subscriber stations are connected to each other such that they can communicate with each other. In this case, the bus system can also have a switch which is connected between at least two of the subscriber stations in order to divide the bus into approximately equally large sections.

The aforementioned object is also achieved by a method for data transmission according to claim 10 in a bus system described above. In the case of the method, a transmitting/receiving device is used in the bus system for transmitting messages to and/or receiving messages from other user stations of the bus system via the bus, wherein the transmitting/receiving device reduces the differential voltage from a predetermined first voltage value for data transmission in a first time period to a predetermined second voltage value for data transmission in a second time period or again increases the differential voltage from the predetermined second voltage value to the predetermined first voltage value, and the decision threshold for the bits of the message received in the second time period is reduced from a predetermined first threshold for data transmission in the first time period to a predetermined second threshold for data transmission in the second time period or again increases from the predetermined second threshold to the predetermined first threshold, and wherein the subscriber station is designed to: the message is transmitted at a higher data transmission rate during the second time period than during the first time period.

This method provides the same advantages as previously mentioned in relation to the subscriber station.

Other possible implementations of the invention also include combinations of features or embodiments not explicitly mentioned before or below in relation to the embodiments. The person skilled in the art will also add individual aspects as improvements or supplements to the respective basic forms of the invention.

Drawings

Subsequently, the present invention is further described in terms of embodiments with reference to the accompanying drawings. Wherein:

fig. 1 shows a simplified block diagram of a bus system according to a first embodiment;

fig. 2 shows a diagram for elucidating the structure of a message transmitted by a subscriber station of the bus system in accordance with the first embodiment;

fig. 3 shows a simplified structure of the transmitting/receiving means of the first and third subscriber stations according to the first embodiment;

fig. 4 shows a schematic progression of the differential voltage over time for CAN _ H-CAN _ L during an active data transmission in the second subscriber station according to the first exemplary embodiment;

fig. 5 shows a schematic progression of the differential voltage over time for CAN _ H-CAN _ L during an active data transmission in the first or third subscriber station according to the first exemplary embodiment;

fig. 6 shows a schematic progression of the differential voltage over time for CAN _ H-CAN _ L during an active data transmission in the first or third subscriber station according to the second exemplary embodiment;

fig. 7 shows a schematic progression of the differential voltage over time for CAN _ H-CAN _ L during an active data transmission in the first or third subscriber station according to the third exemplary embodiment;

fig. 8 shows a schematic progression of the differential voltage over time for CAN _ H-CAN _ L during an active data transmission in the first and third subscriber stations according to the fourth exemplary embodiment;

fig. 9 shows a simplified structure of the transmitting/receiving devices of the first and third subscriber stations according to the fifth embodiment; and

fig. 10 shows a simplified block diagram of a bus system according to a sixth embodiment.

In the drawings, elements that are the same or functionally the same are provided with the same reference numerals unless otherwise specified.

Detailed Description

Fig. 1 shows a bus system 1, which may be, for example, a CAN bus system, a CAN FD bus system, or the like. The bus system 1 can be used in vehicles, in particular in motor vehicles, aircraft, etc., or in hospitals, etc. However, the bus system 1 is not limited to a CAN bus system.

In fig. 1, a bus system 1 has a plurality of

subscriber stations

10, 20, 30 which are each connected to a bus 40 having a first bus line 41 and a second bus line 42. The bus lines 41, 42 may also be referred to as CAN _ H and CAN _ L and serve to couple in the dominant level in the transmit state. The

messages

45, 46, 47 can be transmitted in the form of signals between the

individual subscriber stations

10, 20, 30 via the bus 40.

Additionally, at least two of the

subscriber stations

10, 20, 30, in this

embodiment subscriber stations

10, 30, are designed to transmit or receive data in the form of messages or signals at a lower level than 5V or 3.3V (which are voltage levels commonly used in digital systems as of today). Messages or signals having a lower level than 5V or 3.3V are also referred to as LV messages in the following, the bits of these LV messages also being referred to as LV bits. In the

subscriber station

10, 30, the voltage of the signal with respect to ground has a value of about 1.2V, or the differential voltage has a value of U ≦ 0.2V_DA value in the range of 1V or less. The differential voltage typically has a value of U at 0.2V ≦ U_DA value in the range of 1V or less.

The

user stations

10, 20, 30 can be, for example, control devices or displays or sensors of a motor vehicle.

As shown in fig. 1, the

subscriber stations

10, 30 each have a communication control device 11, a transmitting/receiving device 12, an error counter 15 and a reflection reduction unit 16. In at least one of the

subscriber stations

10, 30, the error counter 15 may also be part of the communication control device 11. The working principle of the error counter 15 is described in more detail with respect to fig. 5. The subscriber station 20 has, in accordance with fig. 1, a communication control device 11 and a transmitting/receiving device 13. The transmit/receive means 12 of the

subscriber stations

10, 30 and the transmit/receive means 13 of the subscriber station 20, respectively, are connected directly to the bus 40, even if this is not shown in fig. 1.

The communication control means 11 are used to control the communication of the

respective subscriber station

10, 20, 30 with other subscriber stations of the

subscriber stations

10, 20, 30 connected to the bus 40 via the bus 40. The communication control means 11 CAN be implemented like a conventional CAN controller or CAN FD controller. The transmitting/receiving means 12 are used for transmitting

messages

45, 47 and are described in more detail below. The transmitting/receiving means 13 may be implemented like a conventional CAN transceiver or CAN FD transceiver.

With the reflection reducing unit 16, reflections can be suppressed which are formed as a result of open bus line ends, plug connectors or branches in the bus 40. The reflection reduction unit 16 is preferably connected to two buses 40 of the busBetween the

wire cores

41, 42. The reflection-reducing unit 16 can be designed, for example, as a zener diode which converts the differential voltage U across the bus 40 in as many positions as possible_DLimited to a minimum of 0V and a maximum of 2V. In order to be able to suppress reflections also for LV bits, the voltage is limited during the transmission of the LV bit, if necessary additionally to a maximum of 0.5V or even 0.2V. The 0.5V limit is raised in time before the bit with the original level is transmitted, so that the limit acts on 2V. However, a hard limit to 0.5V or 0.2V may result in: standard bits with 2V cannot be transmitted. Action is taken on this so that as many as possible of the

subscriber stations

10, 20, 30 limit the voltage to a maximum of 0.5V or 0.2V only when LV transmission can be expected, but also to a maximum of 0.5V or 0.2V only if the short-circuit current caused by the limitation, i.e. the current through the zener diode, does not exceed a certain value. If the short-circuit current is, for example, greater than 0.3mA, the limit is switched from 0.5V or 0.2V to 2V and thereby allows: standard bits with 2V may be transmitted.

As shown in fig. 2 as voltage U with respect to time t in accordance with message 46 for the CAN frame above fig. 2 and the CAN FD frame below fig. 2, the CAN communication over bus 40 CAN be divided into two different time segments, namely arbitration phases 451, 453, which are shown only schematically, and a data field 452, which is also referred to as a data phase in CAN FD. In CAN-FD, the bit transfer rate of the subsequent data phase is increased to e.g. 2, 4, 8Mbps at the end of the arbitration phase, compared to conventional CAN. Thereby applying: in CAN-FD, the bit transfer rate at the

arbitration stage

451, 452 is less than the bit transfer rate at the data region 452. In the case of CAN-FD, the data region 452 is significantly shortened relative to the data region 452 of the CAN frame.

In the

arbitration phase

451, 453 it is determined that: which of the one or

more user stations

10, 20, 30 of the bus system 1 that are currently transmitting obtains exclusive, conflict-free access to the bus 40 of the bus system 1 at least temporarily. The subscriber station that wins arbitration transmits the valid data of message 46 in data region 452.

Fig. 3 shows the connection of the transmitting/receiving device 12 and the error counter 15 with a value of 7 for the counter state 151 in more detail. In addition to the first connection for the transmit signal Tx and the second connection for the receive signal Rx, the transmit/receive device 12 therefore also has a connection for the bus signals CAN _ H and CAN _ L, a connection LV, in particular the input connection. The transmission/reception device 12 also has a current source 121.

Depending on the signal at the connection LV, the transmitting/receiving device 12 switches to LV operation. In LV operation, the transmitting/receiving means 12 reduce the current source 121 from the usual 33mA to 8.3mA in order to transmit the

LV message

45, 47 with the LV bit. In addition, particularly at the same time, the transmitting/receiving device 12 lowers the decision threshold for receiving LV bits from 1V to half the voltage limit, i.e. for example 0.25V or 0.1V. The transmitting/receiving device 12 likewise, in particular simultaneously, reduces the voltage limit from 2V to preferably 0.5V or 0.2V. The flow of which is illustrated in fig. 4 to 6.

Fig. 4 shows the differential voltage U during the active data transmission of a standard CAN message 46_DThe signal level of (c). Here, in the transmission/reception apparatus 12, the judgment threshold 125 for receiving bits is set to 1V. Therefore, if the differential voltage U is_DRises above 1V during the active data transmission of the standard CAN message 46, a bit is recognized.

In fig. 4, the phase of the effective data transmission of a standard CAN message 46 between two fill bits 60 with a bit duration T1 is shown. The filler bits 60 are embedded by the communication control device 11 after a predetermined time interval in the standard CAN message 46 in order to be able to synchronize the

subscriber stations

10, 20, 30 of the bus system 1.

Therefore, in the case of the standard CAN or the standard CAN FD, the judgment threshold 125 is continuously maintained up to 1V.

In contrast, fig. 5 shows the differential voltage U during the active data transmission of the LV-

CAN messages

45, 47_DThe signal level of (c). In order to achieve the best possible compatibility with the existing standards described above, first of all, even in the case of

LV messages

45, 47, standard-compliant power is transmittedFlat bits, as in the case of a standard CAN message or a standard CAN FD message 46. The level is lowered after the arbitration is successful and LV bit 65 having bit duration T3 is transmitted thereby. In fig. 5, bit duration T3 is only half as long as bit duration T1 of fill bits 60. The LV bit may last 1/8 or 1/32 of the time required by the standard arbitration bit for transmission, among other things. The recessive LV bit 1 has a differential voltage below 0.25V, while the subdominant LV bit 0 has a differential voltage greater than 0.25V. The subdominant LV bit 0 can always be covered by the dominant standard bit 0.

LV messages

45, 47 may be constructed in content identically to standard CAN or CAN FD messages, wherein LV messages with more than 64 bytes are tolerated, the LV bit time in the data section is allowed to be shorter than the arbitration bit time in the header, and the sending of LV bits may be informed in advance by one or more standard bits in the header.

In order to avoid that already existing subscriber stations in the market, such as subscriber station 20, do not recognize errors, padding bits 60 can be embedded in

messages

45, 47 at a standard level and with a standard length at the time intervals normally expected.

Alternatively, the communication control device 11 or the transmission/reception device 12 may be designed to: in addition to the dominant padding bits, the recessive padding bits are created directly in order.

According to fig. 5, in the transmitting/receiving device 12, after the arbitration, a filler bit 60 is first expected or transmitted in the payload data, the duration or bit duration of which is T1, which is equal to the standard length of the filler bit 60. Then, after expiration of a predetermined time T2 equal to half of the duration T1, the decision threshold 121 for the received bits is set to 0.25V. Therefore, if the differential voltage U is_DRises above 0.25V during the active data transmission of a standard CAN message or a standard CAN FD message 46, the signal level is recognized as a bit. Following receipt of the dominant fill bit 60 having a duration of T1 and receipt of the recessive fill bit 60A having another duration of T1, there follows a valid data bit 65 having a bit duration of T3. If the padding bits 60 are received again, the transmitting/receiving device 12 increases the decision threshold 121 for the received bits from 0.25V to 1V again, as shown in fig. 5. In FIG. 5, the second dominant fill is being addedAfter expiration of time period T2 after the start of the identification of fill level 60, decision threshold 121 is switched to decision threshold 125.

The efficient data transmission of

LV messages

45, 47 may be fully compatible with transmission according to the CAN protocol or CAN FD protocol.

In the case of a fully compatible LV-CAN according to fig. 5, therefore,

subscriber stations

10, 30 additionally transmit filler bits 60 with a standard level at the positions expected by standard CAN subscriber station 20 during an active data transmission. The

subscriber station

10, 30 as the LV recipient shifts the decision threshold between 0.25V and 1V depending on whether bits with the original level are expected or LV bits 65 are expected.

When communication is performed in the bus system 1, the two levels of CAN-H and CAN-L fluctuate around 2.5V as long as no standard CAN (fd) message is transmitted. Therefore, the differential voltage is 0V. A typical CAN subscriber, such as subscriber station 20, only recognizes the start of a data transmission when the differential voltage between CAN H and CAN L exceeds a certain threshold, for example 1V.

In the case of a communication in the bus system 1, an LVCAN subscriber station 10 first attempts to transmit an LV message 45 of this LVCAN subscriber station with an LV level. If this is not possible, the subscriber station 10 tries to send the message 45 according to the standard protocol, because this LV message 45 is corrupted/dominated by other LV messages 47, electromagnetic radiation or standard messages 46. The transmission attempt of the LV message 45 starts at the same time as the standard message 46, i.e. after the end of the three Inter-Frame-Space (Inter-Frame-Space) bits. If the LV message 45 should be sent at the same time as the standard message 46, the sender, in this example the subscriber station 10, recognizes this at the latest after the transmission attempt of the first recessive padding 60, i.e. after 6 LV bits, because the differential voltage does not drop below 0.1V or because the voltage rises above 1V. The subscriber station 10 as the LV sender recognizes: the subscriber station 20 wants to send a standard message 46. Since subscriber station 20, as a (standard) sender, is always busy sending the first (Start Of Frame) standard bit after 6 LV bits, subscriber station 10 can attempt to send its LV message 45 as standard message 46 or as a message with a standard header but with LV content without delay as an LV sender.

Under special conditions, such as extreme temperatures, extreme air humidity, short-circuiting with sparks, etc., LV data transmissions may be disturbed for a short time, so that the transmission is interrupted due to erroneous frames. Whenever LV transmission is interrupted due to an error frame, the transmission is repeated again according to the CAN protocol or CAN FD protocol at the original level and the original data transmission rate.

Thus, the transmitting/receiving device 12 has an error counter 15, as described previously in relation to fig. 3. The error counter 15 counts the number of erroneous frames. If multiple messages are transmitted in sequence with an error such that the counter status 151 of the error counter 15 exceeds the threshold, then these messages are still only sent at the original level and original data transmission rate, but not at the LV level and LV data transmission rate. A certain number of messages sent/received without errors causes the counter state 151 of the error counter 15 to be lowered. If the counter state 151 of the error counter 15 is lowered enough, the sending of the LV message is resumed. By using standard level transmission during this time, the bus load may increase to the point that no lower priority messages can be sent anymore. However, since high-priority messages can also be transmitted, safe emergency operation of the vehicle is possible.

Arbitration data with LV level CAN also be sent once all standard CAN users are replaced by LV users. If switching back and forth between levels is eliminated, the transmitting/receiving device 12 can be built more advantageously, since the LV connection can be dispensed with. However, safe emergency operation is then possible without a level increase, simply by reducing the data transmission rate.

FIG. 6 shows the differential voltage U during the active data transmission of LV-

CAN messages

45, 47 in a second embodiment_DThe signal level of (c). Here, the transmission/reception device 12 is constructed in the same manner as in the previous embodiment. In the present exemplary embodiment, however, no synchronization of the

subscriber stations

10, 20, 30 of the bus system 1 is required. Thus, no padding bits with the original level are transmitted60. The transmitting/receiving device 12 CAN therefore switch on the decision threshold 121 continuously during the active data transmission of the

LV CAN message

45, 47, as shown in fig. 6. The signal levels of fig. 6 correspond to a pure LV-CAN, wherein the transmission of the filling bits 60 with the original level is omitted and the decision threshold is permanently kept at 0.25V.

In the case of CAN subscriber stations, which do not need to synchronize or detect the LV level during the duration of the active data transmission, filling bits 60 with the original level are therefore omitted within the active data for a higher data transmission rate.

FIG. 7 shows the differential voltage U during the active data transmission of LV-

CAN messages

45, 47 in a third embodiment_DThe signal level of (c). Here, data transmission similar to that described with respect to fig. 5 is performed. However, in the current embodiment, operation is performed with an LV level difference of + -0.5V instead of +0.5V, as illustrated in FIG. 7. From which a larger voltage rise is obtained than in the case of fig. 5, i.e. 1V instead of 0.5V as in the example of fig. 5.

The influence of the interfering radiation is reduced by a higher voltage rise of 1V than 0.5V with respect to the level difference of + 0.5V. However, at the same time, the data transmission rate can be reduced to 1.6 or 2.4 times.

In a modification, it is likewise conceivable: operating with a LV level difference of + 1V. However, this variant is then no longer fully compatible with the CAN protocol or CAN FD protocol so far.

FIG. 8 shows the differential voltage U during the active data transmission of LV-

CAN messages

45, 47 in a fourth embodiment_DThe signal level of (c). Here, data transmission similar to that described with respect to fig. 6 is performed. However, in the current embodiment, operation is performed with a LV level difference of + -0.5V instead of +0.5V, as previously described with respect to FIG. 7. A larger voltage rise of 1V is obtained instead of 0.5V, as in the example of fig. 6.

Here, too, in a modification, it is likewise conceivable: if the lack of compatibility with the CAN protocol or the CAN FD protocol resulting therefrom is not a problem in the bus system 1, operation is carried out with LV level differences of + 1V.

Fig. 9 shows a transmitting/receiving device 120 of a bus system 1 according to a fifth embodiment. Unlike the previous embodiment, the transmitting/receiving device 120 has two connections, namely one input LVR and one output LVT, instead of one connection LV. The output LVT indicates: standard bits are identified on the bus 40 instead of the expected LV bits. The limitation of the differential voltage is effectively switched to a maximum of 0.5V or 0.2V only when the LV operation is actively switched on via the input LVR. In other cases, the transmission/reception apparatus 120 is constructed in the same manner as the transmission/reception apparatus 12 according to the previous embodiment.

In a further embodiment, transmitting/receiving device 120 may have a connection LVRx for LV receive signals and a connection LVTx for LV transmit signals, which may also be referred to as third and fourth connections of transmitting/receiving device 120. In this way, LV transmission signals or LV reception signals can also already be created by the communication control device 11 or forwarded to it.

In a later development phase, with an additional RX input for transmitting LV bits, a connection LVTx for LV transmit signals and an additional RX input for received LV bits, a connection LVRx for LV receive signals, the LV transmission CAN be modulated in parallel not only during transmission pauses but also if necessary during standard CAN transmission. The modulation can be performed similarly to the case of modulating data onto the power supply line.

Thus, it is possible to transmit

LV messages

45, 47 in parallel with standard CAN or CAN FD messages.

Fig. 10 shows a bus system 2 according to a fifth embodiment. The bus system 2 is implemented for the most part in the same way as described in the bus system 1 according to the first embodiment. However, unlike the bus system 1 according to the first exemplary embodiment, the bus system 2 additionally has a CAN switch 50. The CAN switch 50 is preferably embedded in the middle of the bus 40, thereby creating two separate buses 40.

On the one hand, the CAN switch 50 has the following advantages: only

messages

45, 46, 47 are forwarded, which are of interest to the respective other part of the bus system 2. The bus load is thereby additionally reduced, which further increases the speed of data transmission in the bus system 2 compared to the bus system 1 of the first exemplary embodiment due to the less disruptive data transmission attempts.

On the other hand, the CAN switch 50 has the following advantages: it may be considered that the LV signal is weak and therefore susceptible to interference by electromagnetic radiation. As a result, LV messages are often corrupted in a bus system 2 with far apart

user stations

10, 20, 30 in an unfavorable environment or operating state. To limit radiation, the bus length CAN be reduced by using the CAN switch 50.

The bus systems 1, 2 of the previously described embodiments can contribute with respect to the need for higher and higher data transmission rates, which are driven by the flashing of the program states which become higher and higher in the shortest possible time. This flashing CAN last for example for 2.5 hours and longer for a camera in the case of standard CAN. Ideally, a large number of electrical consumers are switched off during the flashing and thereby the electromagnetic radiation source is switched off. In part, the control devices or user stations of the bus systems 1, 2 are also caused to flash outside the vehicle at special stations. Here, shorter and shielded cables can be used, whereby the radiation can be reduced to a minimum.

All previously described embodiments of the bus system 1, 2, the

subscriber stations

10, 20, 30 and the method can be used individually or in all possible combinations. In particular, all features of the previously described embodiments and/or their modifications can be combined or deleted arbitrarily. In addition, the following modifications are conceivable in particular.

The previously described bus systems 1, 2 according to the embodiments are described in terms of a bus system based on the CAN or CAN FD protocol. However, the bus systems 1, 2 according to different embodiments may also be other types of communication networks. It is advantageous, but not mandatory, to ensure exclusive, collision-free access of the

subscriber stations

10, 20, 30 to the bus 40 or to a common channel of the bus 40 at least for a certain time interval in the bus system 1.

Alternatively to the previous embodiment, the LV sender may have earlier identified that the sub-dominant LV bit is covered by the dominant standard bit by exceeding the differential voltage threshold between 0.1V or 0.25V and 1V.

Alternatively to the previous embodiment, the arbitration may also be performed such that the transition to a large differential voltage is only made when the arbitration according to the new method was not successful and was reset to the standard arbitration.

Alternatively to the previous embodiment, the limit may be raised from 0.2V or 0.5V to 2V if transmission of a message with a standard level can be expected due to a previous collision/error.

The bus systems 1, 2 according to the exemplary embodiments are in particular CAN networks or CAN FD networks or Flex Ray networks or SPI networks.

However, it is also conceivable: one of the two

bus cores

41, 42 is grounded and therefore a ground core and the other of the two

bus cores

41, 42 is a signal core on which the bus signals of the

messages

45, 46, 47 are transmitted.

The number and the arrangement of the

subscriber stations

10, 20, 30 in the bus systems 1, 2 according to these embodiments is arbitrary. In particular, only subscriber station 10 or subscriber station 30 may also be present in the bus systems 1, 2 of the exemplary embodiments.

The functions of the previously described embodiments may be implemented not only in the transmitting/receiving apparatus 12. Additionally or alternatively, the functionality may be integrated into an existing product. It is possible in particular that: the functions considered are either implemented in the transmitting/receiving device 12 as separate electronic modules (chips) or embedded in an integrated overall solution, in which case there is only one electronic module (chip).

Claims

1. A subscriber station (10) for a bus system (1; 2) has a subscriber station

Transmitting/receiving means (12; 120) for transmitting messages (45; 46; 47) to other subscriber stations (20; 30) of the bus system (1; 2) and/or for receiving messages (45; 46; 47) of other subscriber stations of the bus system (1; 2) via a bus (40),

wherein the transmitting/receiving device (12; 120) is designed to: the differential voltage is reduced from a predetermined first voltage value for data transmission in a first time period to a predetermined second voltage value for data transmission in a second time period or is increased again from the predetermined second voltage value to the predetermined first voltage value, and the decision threshold (125, 126) for the reception of the bits of the message (45; 46; 47) in the second time period is reduced from a predetermined first threshold for data transmission in the first time period to a predetermined second threshold for data transmission in the second time period or is increased again from the predetermined second threshold to the predetermined first threshold, and

wherein the subscriber station (10) is designed to: the message (45; 47) is transmitted or received at a higher data transmission rate during the second time period than during the first time period.

2. Subscriber station (10) according to claim 1,

wherein the transmitting/receiving device (12; 120) has a connection end, and wherein the transmitting/receiving device (12; 120) is designed to: lowering or raising the differential voltage and the decision threshold in dependence on the signal at the connection, and/or

Wherein the transmitting/receiving device (12; 120) is designed to: -analyzing the content of the message (45) and lowering the differential voltage and the decision threshold or raising the differential voltage and the decision threshold (125, 126) depending on the content of the message (45).

3. Subscriber station (10) according to claim 1,

wherein the transmitting/receiving means (12; 120)

-has a first connection end and is designed to: generating a differential voltage having a predetermined first voltage value for data transmission from a signal on the first connection terminal;

-having a second connection for receiving bits with a decision threshold (125, 126) having said predetermined first threshold value; and also

-has a third connection end and is designed to: generating a differential voltage having a predetermined second voltage value for data transmission as a function of the signal at the third connection; and also

-having a fourth connection for receiving bits with a decision threshold (125, 126) having said predetermined second threshold value.

4. Subscriber station (10) according to one of the preceding claims,

the subscriber station also has a communication control device (11) which is designed to: transmitting a message (45; 47) in a second time period with the insertion of a filler bit (60) at a position of the filler bit (60) expected when the subscriber stations (10, 20, 30) of the bus system (1; 2) are synchronized, and/or

Wherein the communication control device (11) is designed to: creating the filler bits (60) at such differential voltage levels and data transfer rates during the first time period, and/or

Wherein the communication control device (11) or the transmitting/receiving device (12; 120) is designed to: in addition to the dominant padding bits, the recessive padding bits are created directly in order.

5. Subscriber station (10) according to one of claims 1 to 3,

wherein the first time period is a time period for determining which user stations (10, 20, 30) at least temporarily have exclusive, conflict-free access to the bus (40) or a common channel of the bus (40), and

wherein the second time period is a time period in which the user station (10) has exclusive, conflict-free access to the bus (40) or a common channel of the bus (40).

6. Subscriber station (10) according to one of claims 1 to 3,

wherein the level of the differential voltage has a value in the range of 1V and 3V on average, and/or

Wherein the differential voltage has a value of U at 0.2V ≦ U_DA value in the range of 1V or less.

7. Subscriber station (10) according to one of claims 1 to 3,

wherein the transmitting/receiving device (12; 120) is designed to: modulating the LV transmission in parallel to the transmission at a predetermined first current value, and/or

Wherein the subscriber station (10) has an error counter (15) which is designed to count how many times a transmission attempt is interrupted, and wherein the transmitting/receiving device (12; 120) is designed to switch to a transmitting operation, wherein the differential voltage is switched to the predetermined first voltage value, in order to transmit a message (46) only at the original level and the original data transmission rate when a counter state (151) of the error counter (15) exceeds a predetermined value.

8. Subscriber station (10) according to claim 1,

wherein the bus system (1) is a CAN bus system or a CAN FD bus system, and/or

Wherein at least one reflection reduction unit (16) is arranged in the transmitting/receiving device (12; 120), said reflection reduction unit being connected between two bus cores (41, 42) of the bus (40) in order to reduce reflections in the bus system (1).

9. A bus system (1) having:

a bus (40); and

at least two user stations (10, 20, 30) according to one of the preceding claims, which are connected to one another via the bus (40) such that they can communicate with one another.

10. A method for data transmission in a bus system (1), in which method a transmitting/receiving device (12; 120) is used to transmit messages (45; 46; 47) to other user stations (20; 30) of the bus system (1; 2) and/or to receive messages (45; 46; 47) of other user stations (20; 30) of the bus system (1; 2) via a bus (40), wherein the transmitting/receiving device (12; 120) reduces a differential voltage from a predetermined first voltage value for data transmission in a first time period to a predetermined second voltage value for data transmission in a second time period or again increases from the predetermined second voltage value to the predetermined first voltage value, and a decision threshold (125, 46; 47) for receiving bits of the messages (45; 46; 47) in the second time period is set, 126) Decreases from a first predetermined threshold value for data transmission in a first time period to a second predetermined threshold value for data transmission in a second time period or increases again from the second predetermined threshold value to the first predetermined threshold value, and wherein the subscriber station (10) is designed to: the message (45; 47) is transmitted or received at a higher data transmission rate during the second time period than during the first time period.