Transceiver for a can bus system and method for detecting a short circuit using a can transceiver

A transceiver for a CAN bus system and a method for detecting a short circuit using a CAN transceiver. The transceiver includes a transmitter for transmitting a transmission signal to a first bus wire of a bus of the bus system, exclusive, collision-free access to the bus of the bus system of a user station being at least temporarily ensured in the bus system, and for transmitting the transmission signal to a second bus wire of the bus, a receiver for receiving the bus signal transmitted on the bus wires, and a diagnostic unit for detecting a short circuit in the bus system, the diagnostic unit being designed to carry out a diagnosis only in a predetermined communication phase of the bus signal.

FIELD

The present invention relates to a transceiver for a Controller Area Network (CAN) bus system and a method for detecting a short circuit using a CAN transceiver. The transceiver is usable in particular in a CAN FD bus system for detecting short circuits of individual bus lines or bus wires of a bus of the bus system.

BACKGROUND INFORMATION

The CAN bus system is used for message or data transmission in some technical applications. Examples include communication between sensors and control units in a vehicle, or a technical production facility, etc. In such a bus system, messages are transmitted via the CAN protocol and/or CAN FD protocol, as described in the ISO-11898-1:2015 standard as a CAN protocol specification with CAN FD. In a CAN FD bus system, a data transmission rate of greater than 1 Mbit per second (1 Mbps) is possible, for example 2 Mbit/s, 5 Mbit/s, or some other data transmission rate greater than 1 Mbit/s, etc. In addition, a CAN high-speed (HS) bus system is known for which a data transmission rate of up to 500 Kilobit per second (500 kbit/s) is possible.

The CAN bus system is a communication system in which a bus state is actively driven. In the process, a signal for a bus signal CAN_H and a signal for a bus signal CAN_L are separately driven. Transceivers, also referred to as CAN transceivers, CAN FD transceivers, etc., are generally used for transmitting and receiving in a CAN bus system for the individual communication users.

The transceiver is supplied with voltage via a voltage VCC of 5 V that is applied against ground GND. In a vehicle, for example, voltage VCC is delivered by a battery with a voltage Ubat having a value in particular of 12 V or 14 V.

In a CAN bus system, a transceiver for gateway control units requires a so-called diagnostic capability. Accordingly, the transceiver must detect the following errors for CAN as well as for CAN FD:short circuit of the bus wire for CAN_H to Ubatshort circuit of the bus wire for CAN_H to VCCSVshort circuit of the bus wire for CAN_H to GNDshort circuit of the bus wire for CAN_L to Ubatshort circuit of the bus wire for CAN_L to VCCSVshort circuit of the bus wire for CAN_L to GND.

SUMMARY

An object of the present invention is to provide an example transceiver for a CAN bus system and an example method for detecting a short circuit using a CAN transceiver which address the problems mentioned above.

The object may be achieved by providing an example transceiver for a bus system in accordance with the present invention. The example transceiver includes a transmitter for transmitting a transmission signal to a first bus wire of a bus of the bus system, exclusive, collision-free access to the bus of the bus system by a user station being at least temporarily ensured in the bus system, and for transmitting the transmission signal to a second bus wire of the bus, a receiver for receiving the bus signal transmitted on the bus wires, and a diagnostic unit for detecting a short circuit in the bus system, the diagnostic unit being designed to carry out a diagnosis only in a predetermined communication phase of the bus signal.

The described transceiver may be used to achieve the desired diagnostic capability with regard to short circuits. Accordingly, in particular a short circuit of the bus wires may be reliably detected, for example of CAN_H to Ubat and/or of CAN_H to VCC5V and/or of CAN_H to GND and/or of CAN_L to Ubat and/or of CAN_L to VCC5V and/or of CAN_L to GND.

Another advantage of the transceiver is that a possible short circuit may be detected during operation of the transceiver. The operation of the transceiver is not disturbed by the diagnosis that is carried out.

Further advantageous embodiments of the transceiver are described herein.

The diagnostic unit may possibly be designed to carry out a diagnosis in a communication phase of the bus signal in which the transmission rate of the bus signal is equal to or less than 500 Kilobit per second (kbit/s) when a common mode choke having an inductance of 100 micro-Henries (μH) is connected upstream from the transceiver, and/or in which the transmission rate of the bus signal is lower than in another communication phase of the bus signal.

According to one exemplary embodiment, the diagnostic unit is designed to carry out a diagnosis in an arbitration phase in which a determination is made as to which of the user stations is the next to temporarily obtain the exclusive, collision-free access to the bus of the bus system.

According to another variant, the diagnostic unit may be designed to carry out a diagnosis with regard to a predetermined bit sequence. The predetermined bit sequence determines, for example, the end of a message that is to be transmitted via the bus. In addition, the diagnostic unit may be designed to carry out a diagnosis only with regard to a portion of the predetermined bit sequence. It is also possible to transmit the predetermined bit sequence in a communication phase in which multiple user stations transmit at the same time.

In one particular embodiment, the receiver may include a reception comparator for receiving the bus signals, a communication phase detection block being connected in parallel to the inputs of the reception comparator, and the communication phase detection block being designed for detecting the present communication phase of the bus signal, and the diagnostic unit being designed to activate or deactivate its diagnosis based on the detection result of the communication phase detection block.

The above-described transceiver may be part of a bus system that includes a bus, and at least two user stations that are connected to one another via the bus in such a way that they are able to communicate with one another. At least one of the at least two user stations includes an above-described transceiver.

Moreover, the above-mentioned object may be achieved by an example method for detecting a short circuit using a CAN transceiver in accordance with the present invention. The example method is carried out with a transceiver for a bus system in which exclusive, collision-free access to a bus of the bus system by a user station is at least temporarily ensured. The transceiver includes a transmitter, a receiver, and a diagnostic unit, the method including the steps: transmitting, via the transmitter, a transmission signal to a first bus wire of the bus, transmitting the transmission signal to a second bus wire of the bus, receiving, via the receiver, the bus signal that is transmitted on the bus wires, and carrying out a diagnosis, using the diagnostic unit, only in a predetermined communication phase of the bus signal in order to detect a short circuit in the bus system.

The method provides the same advantages as mentioned above with regard to the transceiver.

Further possible implementations of the present invention also include combinations, not explicitly mentioned, of features or specific embodiments described above or below with regard to the exemplary embodiments. Those skilled in the art will also add individual aspects as enhancements or additions to the particular basic form of the present invention.

Unless stated otherwise, similar or functionally equivalent elements are provided with the same reference numerals in the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG.1shows a bus system1which at least in part may be, for example, a CAN bus system, a CAN FD bus system, etc. Bus system1may be used in a vehicle, in particular a motor vehicle, an aircraft, etc., or in a hospital, etc.

InFIG.1, bus system1includes a plurality of user stations10,20,30, each connected to a bus40including a first bus wire41and a second bus wire42. Bus wires41,42may also be referred to as CAN_H and CAN_L, and are used for coupling the dominant levels in the transmission state. Messages45,46,47in the form of signals may be transmitted between individual user stations10,20,30via bus40. User stations10,20,30may be, for example, control units or display devices of a motor vehicle.

As shown inFIG.1, user stations10,30each include a communication control device11and a transceiver12. Transceivers12each include a diagnostic unit15. In contrast, user station20includes a communication control device11and a transceiver13. Transceiver13includes a diagnostic unit16. Transceivers12of user stations10,30and transceiver13of user station20are each directly connected to bus40, even though this is not illustrated inFIG.1.

Communication control device11is used for controlling a communication of the particular user station10,20,30via bus40with another user station of user stations10,20,30connected to bus40. Transceiver12is used for transmitting and receiving messages45,47in the form of signals, and uses diagnostic unit15, as described below in greater detail. Communication control device11may in particular be designed as a conventional CAN FD controller and/or a CAN controller. Transceiver12may, in particular, be a conventional CAN transceiver and/or CAN FD transceiver. Transceiver13is used for transmitting and receiving messages46in the form of signals, and uses diagnostic unit16, as described below in greater detail. Otherwise, transceiver13may be designed as a conventional CAN transceiver.

FIG.2shows the basic design of transceiver12together with diagnostic unit15and a memory unit18. Transceiver12is connected at terminals126,127to bus40, more precisely, first bus wire41of the bus for CAN_H and second bus wire42of the bus for CAN_L, via a common mode choke50. Common mode choke50has an inductance of 100 pH, for example. At transceiver12, the voltage supply, in particular the CAN supply, for first and second bus wires41,42is provided via a terminal128. The connection of transceiver12to ground, i.e., CAN_GND, is established via a terminal129. In the example shown, a terminating resistor49is provided for terminating first and second bus wires41,42.

In transceiver12, first and second bus wires41,42are connected to a transmitter121and to a receiver122. A connector unit125for driving signals via terminals111,112to communication control device11is connected to transmitter121and to receiver122.

For driving the signals of terminals111,112, connector unit125includes a transmission signal driver1251for a transmission signal TxD, also referred to as a TxD signal, that is received at terminal111by communication control device11. In addition, connector unit125includes a reception signal driver1252for a reception signal RxD, also referred to as an RxD signal. Reception signal RxD has been received by bus wires41,42with the aid of receiver122, and is relayed to communication control device11via terminal112. Drivers1251,1252are connected to transmitter121and receiver122via a digital part1253. Digital part1253may carry out monitoring of signals TxD, RxD.

According toFIG.2, transmitter121includes a conventional driver1211for signal CAN_H for first bus wire41, and a conventional driver1212for the signal for CAN_L for second bus wire42.

Receiver122includes a reception comparator1221whose inputs are connected in a resistive, in particular symmetrical, voltage divider1222, more precisely, the center tap thereof, a bus bias voltage unit1223, and a communication phase detection block1225. Bus bias voltage unit1223feeds resistive voltage divider1222at its one end with a predetermined bus bias voltage or a predetermined bus bias voltage potential. At its other end, resistive voltage divider1222is connected to first and second bus wires41,42. The inputs of reception comparator1221are connected in parallel to the inputs of communication phase detection block1225. As shown in the example inFIG.2, communication phase detection block1225may include a differential amplifier whose inputs are connected in parallel to the inputs of reception comparator1221.

Communication phase detection block153may detect and recognize or differentiate the different phases of a communication on bus40, explained below with reference toFIG.3.

Diagnostic unit15diagnoses or checks, based on the detection result of communication phase detection block1225, whether or not a short circuit is present on bus wires41,42. Diagnostic unit15carries out its diagnosis only when a predetermined phase of the communication is present. In other words, diagnostic unit15is designed to activate or deactivate its diagnosis based on the detection result of communication phase detection block1225.

The result of the detection via diagnostic unit15is written into memory unit18in registers181,182. Registers181,182may be read out as needed, so that, for example, a warning message may be output when a short circuit is detected.

According toFIG.3, the information and data to be transmitted in a message45, as well as messages46,47, are stored in bytes or bits, which may assume two different bit states or voltage states. The different bit states of a transmission signal T×D thus have different bus states401,402during transmission of message45,46,47via bus40. In the example shown, first bus state401corresponds to a dominant bus state. Second bus state402corresponds to a recessive bus state.

The upper part ofFIG.3shows, with reference to message45, a CAN frame that is transmitted by transceiver12or transceiver13. The lower part ofFIG.3shows a CAN FD frame, which may alternatively be transmitted by transceiver12.

For the CAN communication on bus40, the CAN frame and the CAN FD frame are basically divided into two different communication phases, namely, arbitration phases451,453, and a data area452, which for the CAN HS is also referred to as a data field, and which for the CAN FD is also referred to as a data phase. Data area452on its end is terminated with at least one end bit454, also referred to as end-of-frame (EOF) or end-of-message. For CAN or CAN FD, the EOF is a bit sequence made up of 11 recessive bits, i.e., bits having second bus state402. The at least one end bit454is preceded by an acknowledgement phase455.

For CAN FD, in comparison to the conventional CAN, the bit rate for the subsequent data phase increases to 2, 4, 8 Mbps, for example, at the end of arbitration phase451. As a result, for CAN FD the bit rate in arbitration phases451,453is lower than the bit rate in data area452. For CAN FD, data area452is greatly shortened compared to data area452of the CAN frame.

In a CAN frame and a CAN FD frame, arbitration phases451,453are used to decide which node or which user station10,20,30of bus system1is carrying most important message45,46,47. User station10,20,30with most important message45,46,47wins the arbitration and therefore is permitted to transmit the message after conclusion of the arbitration phase. All other user stations are then “listeners” during transmission of this most important message. Transceivers12,13drive bus40with low impedance to establish a dominant bus state402or bit state as one of the two different bus states401,402or bit states. In contrast, in the recessive state, as the other of the two different bus states401,402, transceivers12,13have relatively high impedance.

Communication phase detection block1225inFIG.2may in particular recognize arbitration phases451,453, data area452, and the end of data area453, i.e., the least one end bit (EOF)454.

Thus, the functionality of diagnostic unit15may be utilized, as desired, only for communication phases in which the data transmission rate in a CAN frame or CAN FD frame is lower than in other communication phases. As a result, the diagnosis by diagnostic unit15is carried out in the slower phases of the communication in bus system1. For a common mode choke50having an inductance of 100 pH, such communication phases having a lower transmission rate are less than or equal to in particular 500 kbit/s. At 500 kbit/s, a bit lasts 2 μs. In particular, such a communication phase in a CAN frame or CAN FD frame is arbitration phase451,453.

If common mode choke50has an inductance of less than 100 pH, it would be possible to carry out the diagnosis by diagnostic unit15at a transmission rate of greater than or equal to 500 kbit/s. Conversely, for inductance values of common mode choke50greater than 100 pH, the diagnosis by diagnostic unit15is to be carried out at a transmission rate lower than 500 kbit/s.

In the present exemplary embodiment, diagnostic unit15carries out a diagnosis only in arbitration phases451,453.

This ensures that transceiver12is able to reliably detect short circuits. This also applies when, after a transition from recessive to dominant, i.e., from second bus state402to first bus state401, transceiver12, decoupled by choke50, is to create a dominant state for a time of approximately 1 μs. In the stated case, a short circuit on the bus side cannot be detected during such a time window. Diagnostic unit15is therefore designed in such a way that a time period much greater than 1 μs is awaited after a transition from recessive to dominant, before bus voltages CAN_H, CAN_L and/or their differential voltage VDIFF are/is detected for a diagnosis. The stated time period ensures that waiting is carried out for a waiting period until the oscillations, which arise after a transition from recessive to dominant, i.e., from second bus state402to first bus state401, in bus voltages CAN_H, CAN_L die down. The oscillations result from common mode choke50and parasitic capacitances. The stated waiting period results in a time window for the diagnosis by diagnostic unit15which is independent of the bit rate in the CAN frame or the CAN FD frame. However, the time window is determined by the transmission levels of transceiver12and the time constant of common mode choke50.

In one modification of transceiver12, the assessment of whether or not a short circuit is present is carried out is based only on dominant states, i.e., first bus states401. The dominant states may be detected in arbitration phases451,453in comparison to short circuits.

According toFIG.4, transceiver13has essentially the same design as transceiver12. However, transceiver13includes diagnostic unit16instead of diagnostic unit15.

Diagnostic unit16is designed, for example, to carry out the diagnosis with regard to a possibly present short circuit based only on recessive states of a CAN frame or a message46, or based on bits having second bus state402. Diagnostic unit16may in particular test the at least one end bit (EOF)454to decide whether or not a short circuit is present.

For the at least one end bit (EOF)454, in particular in diagnostic unit16, a filter element161may be provided that recognizes6to11successive recessive bits, i.e., bits having second bus state402. In this regard, the at least one end bit (EOF)454provides a comparatively long time window to carry out the diagnosis in the recessive state. Diagnostic unit16is thus designed to carry out a diagnosis only with regard to a portion of the predetermined bit sequence of the at least one end bit (EOF)454.

Diagnostic unit16also provides reliable detection of short circuits of bus wires41,42.

In one modification of transceiver12or transceiver13, the assessment of whether or not a short circuit is present is carried out based on dominant and recessive states. The dominant states are assessed in particular in arbitration phase451,453.

According to another modification, transceiver12may also include a filter element161for carrying out a diagnosis only with regard to a portion of a predetermined bit sequence.

Thus, diagnostic units15,16are used in each case to carry out a method for detecting a short circuit using the particular transceiver12,13.

According to a second exemplary embodiment, transceiver13, more precisely its diagnostic unit16, is used to carry out the assessment of whether or not a short circuit is present, based on the at least one end bit (EOF)454and based on acknowledgement phase455of the CAN frame according toFIG.3, i.e., a message46. In acknowledgement phase455, which in the CAN frame includes the two bits prior to the at least one end bit (EOF)454, multiple transceivers12,13transmit at the same time. In the case of low-impedance short circuits, the diagnostic results based on acknowledgement phase455would be the same as the diagnostic result during a dominant bit without acknowledgement. Otherwise, in principle other voltage levels or bus states must occur here.

Diagnostic unit16according to the second exemplary embodiment achieves the same advantages as those mentioned with regard to diagnostic units15,16according to the first exemplary embodiment.

All the above-described embodiments of diagnostic units15,16, of transceivers12,13, of user stations10,20,30, of bus system1, and of the method according to the first and second exemplary embodiments carried out therein and modifications thereof may be used individually or in any possible combination. In addition, the following modifications in particular are possible.

Above-described bus system1according to the first and second exemplary embodiments is described with reference to a bus system based on the CAN protocol. However, bus system1according to the first and/or second exemplary embodiment may also be some other type of communications network. It is advantageous, but not necessarily a requirement, that for bus system1, exclusive, collision-free access to bus line40or a shared channel of bus line40by a user station10,20,30is ensured, at least for certain time periods.

Bus system1according to the first and/or second exemplary embodiment and its modifications is in particular a CAN network or a CAN HS network or a CAN FD network or a FlexRay network. However, bus system1may also be some other serial communications network.

The number and configuration of user stations10,20,30in bus system1according to the first and second exemplary embodiments and their modifications is arbitrary. In particular, it is possible for only user stations10or user stations20or user stations30to be present in bus systems1in the first or second exemplary embodiment. Notwithstanding, it is also possible for only diagnostic units15or only diagnostic units16according to the various embodiment variants described above to be present.

The functionality of the exemplary embodiments described above may be implemented in a transceiver12,13or a CAN transceiver, a transceiver chipset, a CAN transceiver chipset, etc. Additionally or alternatively, they may be integrated into existing products. In particular, it is possible to implement the functionality in question either in the transceiver as a separate electronic module (chip), or embedded in an integrated overall approach in which only one electronic module (chip) is present.