DE102016224961A1 - Subscriber station for a bus system and method for data transmission in a bus system - Google Patents

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 subscriber station (10) comprises a transmitting / receiving device (12) for transmitting a message (45; 46; 47) to and / or receiving a message (45; 46; 47) from a further subscriber station (20; 30) of the bus system (1; 2) via a bus (40), wherein the transmitting / receiving device (12) is configured, a differential voltage from a first predetermined voltage value for a data transmission in a first time period to a second predetermined voltage value for a data transmission in a second period of time, or raise again from the second predetermined voltage value to the first predetermined voltage value, and the decision threshold (125, 126) for receiving bits of the message (45; 46; 47) in the second time period from a first predetermined threshold to transmit a data transmission in the first time period to a second predetermined threshold for a data transmission in the second time period ken or again from the second predetermined threshold to the first predetermined threshold, and wherein the subscriber station (10) is configured to receive the messages (45; 47) in the second time period to transmit or receive at a higher data transmission rate than in the first time period.

Description

Technical area

The present invention relates to a subscriber station for a bus system and a method for data transmission in a bus system, in which a protocol for CAN or CAN FD is performed with lower voltage than usual.

State of the art

In vehicles, for example, CAN networks are provided in which messages are transmitted by means of the CAN and / or CAN FD protocol, as described in the current ISO-CD-11898-1 as CAN protocol specification with CAN FD.

With CAN, the data rate can not be further increased in many cases, because otherwise the voltage edges would have to be chosen so steeply that more electromagnetic emissions would be generated than permitted. In earlier times, there was only one long CAN bus connecting all the ECUs in the vehicle. Nowadays there are many shorter CAN buses due to the large number of participants. The short cable lengths ensure a better signal-to-noise ratio.

Increasing communication on the CAN bus requires an increase in data rate beyond CAN FD.

The Applicant was therefore considered to use a bus system instead of the previous CAN bus system, in which a lower voltage (low voltage) than the usual high voltage of 5V or 3.3V used in digital systems is used. Such lower voltage systems are known as LVDS (Low Voltage Digital System).

The problem, however, is that existing bus systems are not compatible with an LVDS subscriber station based on the LVDS system. The LV messages of the LVDS subscriber stations are destroyed by the subscriber stations of the conventional subscriber stations. Therefore, in an existing standard CAN system, all existing subscriber stations must be converted to an LVDS system. This is very expensive and costly.

Disclosure of the 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 solve the aforementioned problems. In particular, a control device for a bus system and a method for data transmission in a bus system are to be provided, in which the data transmission rate on the bus can be further increased compared to previous solutions, so as to accelerate error-free communication via the bus.

The object is achieved by a subscriber station for a bus system with the features of claim 1. The subscriber station comprises a transmitting / receiving device for transmitting a message to and / or receiving a message from a further subscriber station of the bus system via a bus, wherein the transmitting / receiving device is configured, a differential voltage from a first predetermined voltage value for to decrease a data transmission in a first time period to a second predetermined voltage value for a data transmission in a second time period or to raise again from the second predetermined voltage value to the first predetermined voltage value and the decision threshold for the receipt of bits of the message in the second time period from a first predetermined one Threshold for a data transmission in the first time period to a second predetermined threshold for a data transmission in the second time period to lower or again from the second predetermined threshold to the first predetermined threshold, and wherein the subscriber station is configured to transmit the messages in the second time period at a higher data transmission rate than in the first time period.

With the subscriber station, the data transmission rate can be increased many times compared to conventional CAN or CAN FD.

A further advantage is that the LV communication performed by the subscriber station, which runs with a lower voltage than with the otherwise usual high voltage of 5V or 3.3 V in digital systems, a standard CAN or standard CAN FD communication on the bus does not bother. The LVCAN subscriber station generates smaller differential voltages during data transmission than usual. The differential voltages are so small that they can not be detected by standard CAN subscriber stations because the differential voltages are below the decision threshold of 1 V, e.g. at 0.5 V or even negative.

Advantageously, the subscriber station is designed so that standard CAN participants from the described subscriber station performed LV differential voltage changes are tolerant and send no error messages. As a result, several LV-CAN subscriber stations can communicate undisturbed. However, the subscriber station described above is designed so that it can switch to the standard protocol if necessary and then also can exchange information with standard CAN subscriber stations.

The executed by the subscriber station described method is therefore fully compatible with previous CAN bus systems. Standard CAN or standard CAN FD subscriber stations can therefore be gradually replaced in the bus by LV-CAN users.

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

According to one embodiment, the transceiver has a port and is configured to lower the difference voltage and the decision threshold or to increase the difference voltage and the decision threshold depending on a signal at the port. Additionally or alternatively, the transceiver can be configured to evaluate a content of the message and, depending on the content of the message, to lower the differential voltage and the decision threshold or to increase the differential voltage and the decision threshold.

According to one embodiment, the transceiver has a first terminal and is configured to generate a second terminal for receiving the bits with the decision threshold depending on a signal at the first terminal to generate the differential voltage with a first predetermined voltage value for data transmission having the first predetermined threshold and a third terminal and configured to generate the differential voltage having a second predetermined voltage value for data transmission in response to a signal at the third terminal and a fourth terminal for receiving the decision threshold bits which has the second predetermined threshold.

According to an embodiment, the subscriber station further has a communication control device configured to send the messages in the second time period with stuff bits at the locations where the stuff bits are expected in a synchronization of the subscriber stations of the bus system, and / or the communication control device or the transceiver is configured to generate the stuff bit with the differential voltage level and the data transmission rate, as in the first time period. Additionally or alternatively, the communication control device or the transceiver may be configured to create a recessive stuff bit directly in sequence in addition to a dominant stuff bit.

The first time period is preferably a time period in which it is determined which subscriber station at least temporarily receives exclusive, collision-free access to the bus or a common channel of the bus. The second period of time is preferably a period of time in which the subscriber station has exclusive, collision-free access to the bus or a common channel of the bus.

It is conceivable that the levels of the differential voltage have on average values that lie in a range of -1 V and 3 V. Additionally or alternatively, the differential voltage may have a value that is in a range of 0.2V ≦ U _D ≦ 1V.

According to one embodiment, the transceiver can be configured to modulate an LV transmission in parallel to a transmission with the first predetermined current value. Additionally or alternatively, the subscriber station may include an error counter configured to count how many times a transmission attempt is aborted, and wherein the transceiver is configured to switch to a transmission mode in which the differential voltage is switched to the first predetermined voltage mode, to send the messages only at the original level and original data rate when a count of the error counter exceeds a predetermined value.

Possibly the bus system is a CAN bus system or a CAN FD bus system. Additionally or alternatively, it is possible that at least one reflection reduction unit is arranged at the transmitting / receiving device, which is connected between two bus wires of the bus in order to reduce reflections in the bus system.

The subscriber station described above may be part of a bus system, which also includes a bus, via which at least two subscriber stations are connected to each other so 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 equal parts.

The aforementioned object is also achieved by a method for data transmission according to claim 10 in a previously described bus system. In the method, a transmission / reception device for transmitting a message to and / or receiving a message from a further subscriber station of the bus system via a bus is used in the bus system, wherein the transmission / reception device uses a differential voltage from a first predetermined Voltage value for a data transmission in a first time period to a second predetermined voltage value for a data transmission in a second time period decreases or increases again from the second predetermined voltage value to the first predetermined voltage value and the decision threshold for the receipt of bits of the message in the second time period of a first predetermined threshold for a data transmission in the first time period to a second predetermined threshold for a data transmission in the second time period decreases or again from the second predetermined threshold to the first predetermined Schw and the subscriber station is configured to transmit the messages in the second time period at a higher data transmission rate than in the first time period.

The method offers the same advantages as previously mentioned with respect to the subscriber station.

Further possible implementations of the invention also include not explicitly mentioned combinations of features or embodiments described above or below with regard to the exemplary embodiments. The skilled person will also add individual aspects as improvements or additions to the respective basic form of the invention.

list of figures

• 1 ein vereinfachtes Blockschaltbild eines Bussystems gemäß einem ersten Ausführungsbeispiel;
• 2 ein Schaubild zur Veranschaulichung eines Aufbaus einer Nachricht, die von einer Teilnehmerstation des Bussystems gemäß dem ersten Ausführungsbeispiel gesendet wird;
• 3 einen vereinfachten Aufbau einer Sende-/Empfangseinrichtung einer ersten und dritten Teilnehmerstation gemäß dem ersten Ausführungsbeispiel;
• 4 einen schematischen Verlauf einer Differenzspannung von CAN_H - CAN_L über der Zeit während einer Nutzdatenübertragung bei einer zweiten Teilnehmerstation gemäß dem ersten Ausführungsbeispiel;
• 5 einen schematischen Verlauf einer Differenzspannung von CAN_H - CAN_L über der Zeit während einer Nutzdatenübertragung bei der ersten oder dritten Teilnehmerstation gemäß dem ersten Ausführungsbeispiel;
• 6 einen schematischen Verlauf einer Differenzspannung von CAN_H - CAN_L über der Zeit während einer Nutzdatenübertragung bei der ersten oder dritten Teilnehmerstation gemäß einem zweiten Ausführungsbeispiel;
• 7 einen schematischen Verlauf einer Differenzspannung von CAN_H - CAN_L über der Zeit während einer Nutzdatenübertragung bei der ersten oder dritten Teilnehmerstation gemäß einem dritten Ausführungsbeispiel;
• 8 einen schematischen Verlauf einer Differenzspannung von CAN_H - CAN_L über der Zeit während einer Nutzdatenübertragung bei der ersten und dritten Teilnehmerstation gemäß einem vierten Ausführungsbeispiel;
• 9 einen vereinfachten Aufbau einer Sende-/Empfangseinrichtung einer ersten und dritten Teilnehmerstation gemäß einem fünften Ausführungsbeispiel; und
• 10 ein vereinfachtes Blockschaltbild eines Bussystems gemäß einem sechsten Ausführungsbeispiel.

The invention is described in more detail below with reference to the accompanying drawings and to exemplary embodiments. Show it:

• 1 a simplified block diagram of a bus system according to a first embodiment;
• 2 a diagram for illustrating a structure of a message that is sent from a subscriber station of the bus system according to the first embodiment;
• 3 a simplified structure of a transmitting / receiving device of a first and third subscriber station according to the first embodiment;
• 4 a schematic course of a differential voltage of CAN_H - CAN_L over time during a user data transmission at a second subscriber station according to the first embodiment;
• 5 a schematic course of a differential voltage of CAN_H - CAN_L over time during a user data transmission at the first or third subscriber station according to the first embodiment;
• 6 a schematic course of a differential voltage of CAN_H - CAN_L over time during a user data transmission at the first or third subscriber station according to a second embodiment;
• 7 a schematic course of a differential voltage of CAN_H - CAN_L over time during a user data transmission at the first or third subscriber station according to a third embodiment;
• 8th a schematic course of a differential voltage of CAN_H - CAN_L over time during a user data transmission in the first and third subscriber station according to a fourth embodiment;
• 9 a simplified construction of a transmitting / receiving device of a first and third subscriber station according to a fifth embodiment; and
• 10 a simplified block diagram of a bus system according to a sixth embodiment.

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

Description of the embodiments

1 shows a bus system 1 , which may be, for example, a CAN bus system, a CAN FD bus system, etc. The bus system 1 can be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in the hospital, etc. The bus system 1 however, is not limited to a CAN bus system.

In 1 has the bus system 1 a variety of subscriber stations 10 . 20 . 30 , each to a bus 40 with a first busload 41 and a second bus wire 42 are connected. The bus routes 41 . 42 can also be called CAN_H and CAN_L and are used to couple the dominant levels in the send state. About the bus 40 can news 45 . 46 . 47 in the form of signals between the individual subscriber stations 10 . 20 . 30 be transmitted.

In addition, at least two of the subscriber stations 10 . 20 . 30 , in this embodiment, the subscriber stations 10 . 30 , for transmitting or receiving data in the form of messages or signals at a level lower than 5V or 3.3V, which is the usual voltage level in digital systems. Messages or lower level signals than 5V or 3.3V are also referred to below as LV messages whose bits are also referred to as LV bits. At the subscriber stations 10 . 30 the voltage of the signal to ground has a value of about 1.2 V or the differential voltage has a value which is in a range of 0.2 V ≤ U _D ≤ 1 V. The differential voltage signal level usually has a value which is in a range of 0.2V ≦ U _D ≦ 1V.

The subscriber stations 10 . 20 . 30 may be, for example, control devices or display devices or sensors of a motor vehicle.

As in 1 shown have the subscriber stations 10 . 30 each a communication control device 11 a transmitting / receiving device 12 , an error counter 15 and a reflection reduction unit 16 , The error counter 15 may be at least one of the subscriber stations 10 . 30 also part of the communication control device 11 be. The operation of the error counter 15 is with respect to 5 described in more detail. The subscriber station 20 has against it 1 a communication control device 11 and a transceiver 13 , The transmitting / receiving devices 12 the subscriber stations 10 . 30 and the transceiver 13 the subscriber station 20 are each directly to the bus 40 connected, even if this is in 1 not shown.

The communication control device 11 serves to control a communication of the respective subscriber station 10 . 20 . 30 over the bus 40 with another subscriber station to the bus 40 connected subscriber stations 10 . 20 . 30 , The communication control device 11 can be implemented like a conventional CAN controller or CAN FD controller. The transmitting / receiving device 12 used to send the messages 45 . 47 and is described in more detail below. The transmitting / receiving device 13 can be implemented like a conventional CAN transceiver or CAN FD transceiver.

With the reflection reduction unit 16 Reflections can be suppressed by open bus wire ends, connectors or branches in the bus 40 arise. The reflection reduction unit 16 is preferably between the two bus wires 41 . 42 of the bus 40 connected. The reflection reduction unit 16 For example, it can be designed as a Zener diode, which at as many points as possible the differential voltage U _D on the bus 40 to at least 0 V and a maximum of 2V limit. In order to be able to suppress reflections likewise for LV bits, the voltage is limited to a maximum of 0.5 V or even 0.2 V during the transmission of LV bits, if appropriate in addition. In time for the transmission of bits at the original level, the 0.5 V limit is canceled so that the limitation acts on 2 V. However, a hard limit of 0.5 or 0.2 V would mean that no standard 2 V bit can be transmitted. Therefore, the procedure is that only if one can expect a LV transmission, then as many of the subscriber stations 10 . 20 . 30 but the voltage to a maximum of 0.5 or 0.2 V limit only as long as the short-circuit current, which is caused by the limitation, namely the current through the Zener diode, does not exceed a certain value. For example, if the short-circuit current is greater than 0.3mA, the limit is switched from 0.5 or 0.2V to 2V, allowing a standard 2V bit to be sent.

As in 2 based on the message 46 for a CAN frame top in 2 and a CAN FD frame below in 2 each shown as voltage U over time t, CAN communication on the bus 40 are basically divided into two different time periods, namely the Arbitrierungsphasen shown only schematically 451 . 453 and a data area 452 , which is also called data phase in CAN-FD. In CAN-FD, the bit rate for the following data phase is reduced to z. B. 2, 4, 8Mbps increased. Thus, with CAN-FD, the bit rate in the arbitration phases 451 . 453 less than the bit rate in the data area 452 is. For CAN-FD, the data area is 452 opposite the data area 452 significantly shortened the CAN frame.

In the arbitration phase 451 . 453 it is determined which of the currently transmitting subscriber station (s) 10 . 20 . 30 of the bus system 1 at least temporarily exclusive, collision-free access to the bus 40 of the bus system 1 gets. In the data area 452 If there is a transmission of the user data of the message 46 by the subscriber station, which has won the arbitration.

3 shows the connections of a transceiver 12 and the error counter 15 with a value of 7 for the meter reading 151 more accurate. Thus, the transmitting / receiving device has 12 In addition to a first connection for the transmission signal Tx and a second connection for the reception signal Rx, connections for the bus signals CAN_H and CAN_L have a connection LV, which is in particular an input connection. In addition, the transmitting / receiving device has 12 a power source 121 on.

Depending on a signal at the terminal LV, the transmitting / receiving device switches 12 to LV operation. In LV mode, the transceiver lowers 12 the power source 121 from the usual 33 mA to 8.3 mA starting to get an LV message 45 . 47 with LV bits to send. In addition, in particular at the same time, the transmitting / receiving device lowers 12 the decision threshold for the reception of LV bits of 1 V to the half of the voltage limit, for example, 0.25 V or 0.1 V from. Likewise, in particular at the same time, the transmitting / receiving device lowers 12 the voltage limit of 2 V to preferably 0.5 V or 0.2 from. The processes for this are in 4 to 6 illustrated.

4 shows the signal level for a differential voltage U _D during the user data transmission of a standard CAN message 46 , Here is at the transceiver 12 a decision threshold 125 set to 1V for receiving bits. Thus, bits are detected when the signal level for a differential voltage U _D during the Nutzdatenübertragung a standard CAN message 46 rises above 1V.

In 4 is a phase of payload transfer of a standard CAN message 46 between two stuff bits 60 shown with a bit duration T1. The stuff bits 60 are from the communication control device 11 after predetermined time intervals in the standard CAN message 46 inserted to synchronize the subscriber stations 10 . 20 . 30 of the bus system 1 to enable.

With the standard CAN or standard CAN FD, the decision threshold remains 125 constantly at 1 V.

In difference shows 5 the signal level for a differential voltage U _D during the user data transmission of an LV-CAN message 45 . 47 , Here, in order to achieve the best possible compatibility with existing standards described above, even with the LV news 45 . 47 first transmit the bits with normal level, as with a standard CAN message or standard CAN FD message 46 , Only after successful arbitration are the levels reduced and thus LV bits 65 transmitted with a bit duration T3. In 5 the bit duration T3 is only half as long as the bit duration T1 of a stuff bit 60 , In particular, an LV bit may take 1/8 or 1/32 of the time required for a standard arbitration bit to transmit. 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. A subdominant LV bit 0 can always by a dominant standard bit 0 be overdriven. An LV message 45 . 47 The content of the standard CAN or CN FD message may be the same, with LV messages longer than 64 bytes allowed, the LV bit times in the data part shorter than the arbitration bit times in the header, and the sending of LV bits can be announced by one or more standard bits in the header.

Thus already in the market subscriber stations, such as the subscriber station 20 , no errors can detect stuff bits 60 in the usual expected intervals of standard level and standard length in the news 45 . 47 be inserted.

Optionally, the communication control device 11 or the transceiver 12 be designed to create a recessive stuff bit in sequence, in addition to a dominant stuff bit.

According to 5 is at the transceiver 12 after arbitration in the payload first a stuff bit 60 expected or sent, whose duration or bit duration is T1, which is equal to the standard length of stuff bit 60. Thereafter, after lapse of a predetermined time T2 which is equal to half the time T1, a decision threshold 121 set to 0.25V for receiving bits. Thus, signal levels are detected as bits when the signal level for the differential voltage U _D during the payload transmission of a standard CAN message or standard CAN FD message 46 above 0.25V increases. After receiving the dominant stuff bit 60 with the duration T1 and the receipt of a recessive stuff bit 60A with the further time period T1 payload bits follow 65 with a bit duration T3. Will be a stuff bit again 60 receive, lifts the transceiver 12 the decision threshold 121 for the reception of bits again from 0.25 V to 1 V, as in 5 shown. Switching the decision threshold 121 to the decision threshold 125 occurs after the expiration of the period T2 after the beginning of a detection of the second dominant stuff bit 60 in 5 ,

The user data transmission of an LV message 45 . 47 can be fully compatible with a transmission according to the CAN protocol or the CAN FD protocol.

For fully compatible LV-CAN according to 5 send the subscriber stations 10 , 30 additional stuff bits 60 with standard level during the user data transmission to that of the standard CAN subscriber station 20 expected places. The subscriber stations 10 . 30 as an LV receiver, the decision threshold varies between 0.25 V and 1 V depending on whether a bit with an original level or an LV bit 65 is expected.

For communication in the bus system 1 The two levels of CAN-H and CAN-L move around 2.5 V, as long as no standard CAN (FD) messages are sent. The differential voltage is therefore 0 V. Ordinary CAN stations, such as the subscriber station 20 , recognize the start of a data transfer only when the difference voltage between CAN-H and CAN-L exceeds a certain threshold of eg 1V.

For communication in the bus system 1 For example, the LVCAN subscriber station tries 10 first her (LV message) 45 with LV level to send. Is not possible because of another LV message 47 , electromagnetic radiation or a standard message 46 destroyed / dominated, tried the subscriber station 10 the message 45 to ship according to the standard protocol. The transmission attempt of the LV message 45 starts at the same time as a standard message 46 that is, after the end of the three inter-frame-space bits. If an LV message 45 at the same time as a standard message 46 is to be sent, then recognizes the LV transmitter, in this example, the subscriber station 10 , at the latest after the transmission attempt of the first recessive stuff bit 60 that is, 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 LV transmitter recognizes that the subscriber station 20 a standard message 46 would like to send. As the subscriber station 20 as the (standard) transmitter after 6 LV-bits is still busy sending the first (Start Of Frame) standard bit, the subscriber station can 10 as the LV transmitter without delay try their LV message 45 as a standard message 46 or as message with standard header but with LV content to send.

Under special conditions, such as extreme temperatures, extreme humidity, short circuits with a spark, etc., the LV data transmission may be temporarily disturbed, so that the transmission is interrupted by an error frame. Every time an LV transmission is aborted by an error frame, the transmission is repeated again at the original level and original data rate according to the CAN protocol or the CAN FD protocol.

Therefore, the transmitting / receiving device has 12 an error counter 15 on, as before regarding 3 described. The error counter 15 counts the number of error frames. If so many messages are transmitted incorrectly in a row, that the meter reading 151 of the error counter 15 exceeds a threshold, then the messages are sent only at the original level and original data rate instead of LV level and LV data rate. A certain number of messages sent / received without errors reduces the count 151 of the error counter 15 , When the meter reading 151 of the error counter 15 far enough away, the transmission of LV messages is resumed. Due to the intermediate transmission with standard levels, the bus load can increase so much that low-priority messages can no longer be sent. However, as a result of the fact that the high-priority messages can still be sent, safe emergency operation of the vehicle is possible.

As soon as all normal CAN stations have been replaced by LV stations, the arbitration data can also be sent with LV levels. If you do not need to toggle between levels, the transceivers can 12 be built cheaper because the LV connection can be omitted. However, then a safe emergency operation is only possible by reducing the data rate without level increase.

6 shows the signal level for a differential voltage U _D during the user data transmission of an LV-CAN message 45 . 47 in a second embodiment. Here is the transceiver 12 constructed in the same way as in the previous embodiment. However, in the present embodiment, there is no synchronization of the subscriber stations 10 . 20 . 30 of the bus system 1 required. Therefore, no stuff bits 60 transmitted at original level. As a result, the transmitting / receiving device 12 during the user data transmission of an LV-CAN message 45 . 47 throughout the decision threshold 121 turn on as in 6 shown. The signal level of 6 corresponds to a pure LV-CAN, in which to send the stuff bits 60 is dispensed with the original level and the decision threshold remains permanently at 0.25V.

Thus, in the case of CAN subscriber stations which need no synchronization over the duration of the user data transmission or can detect LV levels, the stuff bits 60 be dispensed with original level within the payload in favor of a higher data transfer rate.

7 shows the signal level for a differential voltage U _D during the user data transmission of an LV-CAN message 45 . 47 in a third embodiment. Here is a similar data transmission as in relation to 5 described. However, in the present embodiment, an LV level difference of + -0.5V instead of +0.5V is used, as in FIG 7 illustrated. This results in a larger voltage swing than in the case of 5 , namely 1 V instead of 0.5 V, as in the example of 5 ,

Compared to level differences of +0.5 V, the influence of interference radiation is reduced by the larger voltage swing of 1 V instead of 0.5 V. However, at the same time, the data transmission rate should be reduced to 1.6 or 2.4 times.

In a modification, it is also conceivable to work with an LV level difference of +1 V. However, this change is then no longer fully compatible with the previous CAN protocol or CAN FD protocol.

8th shows the signal level for a differential voltage U _D during the user data transmission of an LV-CAN message 45 . 47 in a fourth embodiment. Here is a similar data transmission as in relation to 6 described. However, in the present embodiment, an LV level difference of + -0.5V instead of +0.5V is used, as previously discussed with respect to FIG 7 described. This results in a larger voltage swing of 1 V instead of 0.5 V, as in the example of 6 ,

Again, it is also conceivable in a modification to work with an LV level difference of +1 V, if the resulting lack of compatibility with the CAN protocol or CAN FD protocol in the bus system 1 is not a problem.

9 shows a transmitting / receiving device 120 for a bus system 1 according to a fifth embodiment. In contrast to the preceding embodiments, the transceiver has 120 instead of one connection LV two connections, namely an input LVR and an output LVT. The LVT output indicates when, instead of an expected LV bit, a standard bit on the bus 40 was detected. Only when the LV operation is activated by the LVR input, the limitation of the differential voltage is switched to a maximum of 0.5 V or 0.2 V active. Otherwise, the transmitting / receiving device 120 constructed in the same way as the transceiver 12 according to the preceding embodiments.

In yet another embodiment, the transmitting / receiving device 120 a LVRx terminal for the LV receive signal and a LVTx terminal for the LV transmit signal, also as the third and fourth terminals of the transceiver 120 can be designated. In this way, the LV transmission signal or LV reception signal also already from the communication control device 11 be created or passed on to them.

With the additional RX input for sending LV bits, the LVTx connection for the LV transmit signal and the additional RX input for received LV bits, the LV receive signal LVRx for the LV receive signal can not only be used later in development steps the transmission pauses but possibly also during a standard CAN transmission an LV transmission are modulated in parallel. The modulation may be similar to modulating data onto a power line.

This would be a transmission of LV messages 45 . 47 parallel to standard CAN or CAN FD messages possible.

10 shows a bus system 2 according to a fifth embodiment. The bus system 2 is performed in much the same way as in the bus system 1 described according to the first embodiment. In contrast to the bus system 1 According to the first embodiment, the bus system 2 but additionally a CAN switch 50 , The CAN switch 50 is preferably in the middle of the bus 40 built in, creating two separate buses 40 be generated.

The CAN switch 50 has the advantage that only the news 45 . 46 , 47 are forwarded to the other part of the bus system 2 are of interest. As a result, the bus load decreases in addition, which, because of fewer interrupted data transmission attempts, the speed of data transmission in the bus system 2 opposite the bus system 1 of the first embodiment further increased.

On the other hand, the CAN switch 50 the advantage that it can be taken into account that the LV signals are very weak and thus prone to electromagnetic radiation. Therefore, LV messages are in bus systems 2 with distant subscriber stations 10 . 20 . 30 In unfavorable environment or operating conditions often destroyed. To limit the irradiation, the bus length can be reduced by using the CAN switch 50 be reduced.

The bus systems 1 . 2 The embodiments described above can make a contribution in terms of ever-higher data rates are needed, which is driven by flashing ever-increasing program levels in the shortest possible time. Flashing can take 2.5 hours and more with standard CAN eg for cameras. Ideally, many electrical consumers are switched off during flashing and thus turned off electromagnetic Einstrahlquellen. In part, the control units or subscriber stations of the bus system 1 . 2 also flashed outside the vehicle at special stations. Shorter and shielded cables can be used here, which reduces the radiation to a minimum.

All previously described embodiments of the bus systems 1 . 2 the subscriber stations 10 . 20 . 30 and the method can be used individually or in all possible combinations. In particular, all the features of the previously described embodiments and / or their modifications can be arbitrarily combined or omitted. In addition, the following modifications are conceivable, in particular.

The bus system described above 1 . 2 according to the embodiments is described with reference to a based on the CAN protocol or CAN FD protocol bus system. The bus system 1 . 2 however, according to the various embodiments may also be another type of communication network. It is advantageous, but not necessarily a requirement, that in the bus system 1 . 2 at least for certain periods of time an exclusive, collision-free access of a subscriber station 10 . 20 30 on the bus 40 or a common channel of the bus 40 is guaranteed.

As an alternative to the previous embodiments, the LV transmitter can detect overshoot of the subdominant LV bit by a dominant standard bit by exceeding a differential voltage threshold between 0.1V or 0.25V and 1V earlier.

As an alternative to the preceding embodiments, arbitration can also be carried out in such a way that it is only switched to large differential voltages if the arbitration according to the new method was unsuccessful and was reset to standard arbitration.

As an alternative to the preceding embodiments, the limitation may be increased from 0.2 V or 0.5 V to 2 V if the previous collisions / errors can be expected to send a standard level message.

The bus system 1 . 2 According to the embodiments, in particular, a CAN network or a CAN FD network or a FlexRay network or an SPI network.

However, it is also conceivable that one of the two bus routes 41 . 42 connected to ground and thus is a Masseader and the other of the two bus wires 41, 42 is a signal wire on which the bus signal for the messages 45 . 46 , 47 is transmitted.

The number and arrangement of subscriber stations 10 . 20 . 30 in the bus system 1 . 2 according to the embodiments is arbitrary. In particular, only subscriber stations can 10 or subscriber stations 30 in the bus systems 1 . 2 the embodiments may be present.

The functionality of the embodiments described above can be not only in a transmitting / receiving device 12 implement. Additionally or alternatively, the functionality can be integrated into existing products. In particular, it is possible that the functionality under consideration either in a transmitting / receiving device 12 is realized as a separate electronic component (chip) or embedded in an integrated overall solution in which only one electronic component (chip) is present.

Claims (10)

Subscriber station (10) for a bus system (1; 2), with a transmitting / receiving device (12; 120) for transmitting a message (45; 46; 47) to and / or receiving a message (45; 46; 47) from a further subscriber station (20; 30) of the bus system (1; 2) via a bus (40), wherein the transceiver device (12; 120) is configured to lower a differential voltage from a first predetermined voltage value for a data transmission in a first time period to a second predetermined voltage value for a data transmission in a second time period or again from the second predetermined voltage value to the second and a decision threshold (125, 126) for receiving bits of the message (45; 46; 47) in the second time period from a first predetermined threshold for data transmission in the first time period to a second predetermined threshold for data transmission in the second period or to raise again from the second predetermined threshold to the first predetermined threshold, and wherein the subscriber station (10) is configured to transmit or receive the messages (45; 47) in the second time period at a higher data transmission rate than in the first time period. Subscriber station (10) to Claim 1 wherein the transceiver (12; 120) has a port (LV), and wherein the transceiver (12; 120) is configured to lower the differential voltage and the decision threshold, depending on a signal at the port (LV) increase the difference voltage and the decision threshold, and / or wherein the transceiver (12; 120) is configured to evaluate a content of the message (45) and, depending on the content of the message (45), to decrease the difference voltage and the decision threshold or Difference voltage and the decision threshold (125, 126) increase. Subscriber station (10) to Claim 1 or 2 wherein the transceiver means (12; 120) has a first terminal (Tx) and is configured to generate the differential voltage at a first predetermined voltage value for data transmission depending on a signal at the first terminal (Tx); second terminal (Rx) for receiving the decision threshold bits (125, 126) having the first predetermined threshold, and - having a third terminal (LVTx) and being configured, depending on a signal at the third terminal, the differential voltage having a second predetermined voltage value for data transmission, and having a fourth terminal (LVRx) for receiving the decision threshold bits (125, 126) having the second predetermined threshold. Subscriber station (10) according to one of the preceding claims, further comprising communication control means (11) arranged to send the messages (45; 47) in the second time period with stuff bits (60) at the locations where the stuff bits (60) synchronize the subscriber stations (10, 20, 30) of the bus system (1, 2) are expected, and / or wherein the communication control means (11) is arranged to generate the stuff bits (60) at the differential voltage level and the data transfer rate as in the first time period, and / or wherein the communication control means (11) or the transceiver means (12; 120) is arranged to create a recessive stuff bit in direct succession in addition to a dominant stuff bit. Subscriber station (10) according to one of the preceding claims, wherein the first time period is a time period in which it is determined which subscriber station (10, 20, 30) at least temporarily receives exclusive, collision-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 subscriber station (10) has exclusive, collision-free access to the bus (40) or a common channel of the bus (40). Subscriber station (10) according to one of the preceding claims, wherein levels of the differential voltage have on average values which lie in a range of 1 V and 3 V, and / or wherein the differential voltage has a value which is in a range of 0.2 V ≤ U _D ≤ 1V. Subscriber station (10) according to one of the preceding claims, wherein the transceiver (12; 120) is configured to parallel modulate an LV transmission upon transmission with the first predetermined current value, and / or wherein the subscriber station (10) has an error counter (15) configured to count how many times a transmission attempt is aborted, and wherein the transceiver (12; 120) is configured to switch to a transmission mode in which the differential voltage is switched to the first predetermined voltage value to send the messages (46) only at the original level and original data rate when a count (151) of the error counter (15) exceeds a predetermined value. Subscriber station (10) for a bus system (1), wherein the bus system (1) is a CAN bus system or a CAN FD bus system, and / or wherein at the transmitting / receiving means (12; 120) at least one reflection reduction unit (16) is arranged, which is connected between two bus wires (41, 42) of the bus (40) to reduce reflections in the bus system (1). Bus system (1), with a bus (40), and at least two subscriber 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. Method for data transmission in a bus system (1) in which a transmitting / receiving device (12; 120) for transmitting a message (45; 46; 47) to and / or receiving a message (45; 46; 47) from a r another subscriber station (20; 30) of the bus system (1; 2) is used via a bus (40), wherein the transceiver means (12; 120) applies a differential voltage from a first predetermined voltage value for a data transmission in a first time period to a second predetermined voltage value for a data transmission in a second time period or to raise again from the second predetermined voltage value to the first predetermined voltage value and a decision threshold (125, 126) for receiving bits of the message (45; 46; 47) in the second time period from a first predetermined threshold for data transmission in the first time period to a second predetermined threshold for data transmission in decreases from the second period or again from the second predetermined threshold to the first predetermined threshold and wherein the subscriber station (10) is arranged to transmit or receive the messages (45; 47) in the second time period at a higher data transmission rate than in the first time period.

Images