WO2003005659A2 - Line code for data transmission in a motor vehicle - Google Patents

Abstract

According to the invention, the channel coding for a transmission channel is carried out in such a way that a character repertoire for the signal to be emitted contains at least n+1 characters, if the character repertoire for an input signal to be transmitted has n characters. In addition, a signal unit of the input signal that is occupied by a character has the same duration as a signal unit in the signal to be emitted. The coding rule also stipulates that two consecutive signal units in the signal to be emitted contain different characters.

Description

description

Output unit, receiving unit, arrangement for data transmission in a motor vehicle and method therefor

The invention relates to a unit for outputting a signal on a transmission channel in a motor vehicle, a unit for receiving a signal from a transmission channel in a motor vehicle, an arrangement for data transmission in a motor vehicle via a transmission channel and a method for data transmission in a motor vehicle.

Motor vehicles often have distributed control or computing units. Such distributed control or computing units are usually understood to mean units which are arranged at different points in the motor vehicle. Because of their need to exchange data, these control and computing units are connected to one another via a transmission channel — contactless or wired. In this case, for example, sensors arranged in the engine compartment, in the doors or in the tires transmit data to central processing units which use the received data algorithmically and actuate corresponding actuators. The data transmission between the above-mentioned units is usually carried out asynchronously. To correctly reconstruct the data in the receiver, the receiver must therefore know the clock information of the sending unit. Because of this, this clock information must be transmitted over the transmission path from the transmitter to the receiver. If clock information is transmitted in addition to the other information, the transmission bandwidth increases. The data transmission has an overhead.

The data generated in a unit - for example a sensor - are encoded for the purpose of data transmission to a remote location in this unit. The experts here also speak of channel coding, which generates the brings data into a form suitable for transmission. This takes place on the basis of a coding rule which transcodes the input signal into the signal to be transmitted. In the following, the term input signal is always used for the signal present in the transmitter, the information of which is to be transmitted to the receiver.

In automotive engineering, such input signals are usually encoded according to the NRZ code or the Manchester code and then transmitted. In this context, FIG. 2 shows these known coding methods for data transmission in a motor vehicle.

FIG. 2a shows an input signal DATA over time t, the information of which is to be transmitted to a receiver via a transmission channel. The input signal DATA is binary coded, that is, it has a character set of two characters, namely a 0 and a 1. Individual signal units of the input signal DATA have a duration T. Several such signal units lined up and each occupied with one character from the character set result in a data word that is physically present as a signal, characterized by its voltage or current states. FIG. 2b shows a work cycle TAKT of the sending output unit

FIGS. 2c and 2d show signals CHAN that are associated with the input signal DATA and are channel-coded according to certain coding regulations, FIG. 2c shows a signal CHAN to be transmitted that was obtained from the input signal DATA after the NRZ coding. This coding is initially a 1: 1 mapping of the input signal. With the UART (Universal Asynchronous Receive Transmit) standard, the receiver is only synchronized by a start signal. The free-running oscillator provided in the receiver for clock generation may have a predetermined tolerance range until further synchronization with the transmitter by another Do not leave the start signal. This either requires a high-precision oscillator in the receiving unit, or else high-frequency synchronization, which is at the expense of the transmission bandwidth.

FIG. 2d shows a channel-coded signal CHAN to be transmitted, which was obtained from the input signal DATA by Manchester coding. Manchester coding is characterized by the fact that, like NRZ coding, it uses a binary character set. Within a signal unit T of the input signal, however, two characters / signal states are provided in the manchester-coded signal. The change from one character of the input signal to its complementary character in the subsequent signal state is implemented by the Manchester code by a phase change. The Manchester Code thus offers the possibility of clock recovery in the receiver within a theoretical tolerance range of 50%. However, this option of clock recovery is purchased by doubling the bandwidth, since one signal unit (bit) of the input signal is represented by two signal states during the same time period T in the signal to be transmitted.

A channel coding based on current modulation is known from WO 98/52 792-A. The channel coding has a character set of three characters, HIGH, LOW and zero. The input signal provides a binary code. According to the coding regulation, ones of the input signal are alternately coded in HIGH and LOW pulses in the signal to be transmitted. Zeros of the input signal remain zero levels in the signal to be transmitted.

In this known data transmission method, the time average of the signals to be transmitted is kept constant. However, no work cycle can be derived from the signal to be transmitted. A data transmission method is known from EP 0 384 258 A2, in which a binary input signal is channel-coded by means of an AMI (Alternate Mark Inversion) code in connection with a pulse width modulation. The input signal is first pulse-width modulated before the pulse-width-coded signal thus formed is subjected to an alternate mark inversion.

A disadvantage of this data transmission method is the increased bandwidth in the signal to be transmitted compared to the input signal. In addition, the narrow pulses generated by pulse width modulation pose EMC problems.

It is therefore the object of the invention to provide an arrangement for transmitting data in a motor vehicle, an associated output unit and an associated receiving unit and a data transmission method in which the transmission bandwidth is kept small and nevertheless sufficient information about the work cycle is transmitted to the receiving unit.

The part of the task relating to the output unit is solved by the features of patent claim 1.

The part of the task relating to the receiving unit is solved by the features of patent claim 6.

The part of the task relating to the arrangement is solved by the features of patent claim 11.

The part of the object of the invention relating to the method is solved by the features of patent claim 12.

In the invention, the channel coding is carried out in such a way that the code for the signal to be transmitted via the channel contains at least one more character in its character set than the character set from which the input signal is formed whose information is ultimately to be transmitted. So z. B. be provided for the input signal, a binary code, then the signal to be transmitted is formed at least from a ternary code, ie there are three different characters, which are represented for example by three different signal states on the line, available to form a signal. Generally, n characters are available for the input signal, with n as an integer, and at least n + 1 characters for the signal to be transmitted.

It should also be noted that in the channel coding according to the invention a signal unit of the input signal is mapped one to one onto a signal unit of the signal to be transmitted. The signal units of the input signal and the signal to be transmitted thus have the same duration. In addition, the invention provides that in the signal to be transmitted, two successive signal units always have different characters from the assigned character set. The implementation of this feature is achieved in that the character set of the channel code comprises one character more than the character set assigned to the input signal. Thus, a change of character and thus a change of state can always take place in the signal to be transmitted, even if the input signal has the same character and thus the same state across several signal units.

The continuous change of state in the signal to be transmitted in turn now contributes to the fact that the working cycle of the remotely located output unit can be easily recovered in the receiving unit. Since the time units of the signal units of the input signal in the output unit and of the signal received by the receiving unit correspond and a change of state occurs after each signal unit, the receiving unit only needs to detect the change of state in the received signal in order to derive the operating cycle of the output unit can. At the same time, however, the bandwidth is not increased, e.g. B. in the Manchester coding introduced at the outset, since the time units for the individual bits (signal units) are always of the same duration.

The advantage of the invention is that no or only imprecise oscillators have to be used in the receiver. This allows a more economical overall arrangement. The inaccurate oscillators can be integrated on a chip. Standard bus drivers can also be used.

The invention can always be used in a motor vehicle as soon as data are to be transmitted between two computing or control units. The invention is used in particular where sensor data from sensors distributed over the vehicle are connected to control units arranged in the vehicle center and feed these control units with sensor data. In particular, the invention is used in occupant protection technology for the transmission of sensor data from impact sensors arranged on the vehicle front or on the vehicle sides to an evaluation unit arranged in the vehicle center. The impact sensors can be acceleration sensors with downstream signal processing and a corresponding interface, or they can also be pressure sensors.

Advantageous developments of the invention are characterized by the subclaims.

Embodiments of the invention and its developments are explained in more detail below with reference to the drawings.

Show it:

FIG. 1 signal curves for the coding method according to the invention, FIG. 2 signal curves belonging to known coding methods reindeer,

FIG. 3 shows a block diagram of an arrangement according to the invention,

FIG. 4 shows a CAN driver arrangement of an output unit according to the invention,

FIG. 5 shows a receiving unit according to the invention,

FIG. 6 shows a table for driver activation of an output unit according to the invention and a reception unit according to the invention,

FIG. 7 shows a signal curve with respect to a two-wire transmission medium in accordance with ISO 11898,

FIG. 8 components of an output unit according to the invention,

FIG. 9 shows a status table associated with the output unit according to FIG. 8,

FIG. 10 shows another exemplary embodiment of a receiving unit according to the invention,

FIG. 11 shows a status table belonging to the receiving unit according to FIG. 10.

The same elements or signals are given the same reference symbols across the entire frame.

Figure la shows an exemplary binary input signal DATA over time t with exemplary four signal units (bits), each of a time duration T. The binary character set is exhausted in a HIGH and a LOW character. The HIGH symbol is identified in the output unit by a 5 volt voltage state, the LOW symbol by a 0 volt voltage state. The exemplary input signal DATA contains the following characters sequentially: HIGH, LOW, LOW, HIGH.

This input signal DATA is to be transmitted via a transmission channel in the motor vehicle. It is in the output unit. The output unit contains a coding unit with a coding rule for transcoding the input signal DATA into a signal CHAN to be transmitted via the transmission channel, which is then output to the transmission signal.

The signal CHAN to be transmitted associated with the input signal DATA according to FIG. 1a can be seen according to FIG. 1b. Basically, a character set with three characters - HIGH, LOW, NULL - is provided for the signal CHAN to be transmitted. Each signal unit of the input signal DATA corresponds to a signal unit of the signal CHAN to be transmitted. The bit times are therefore the same in both signals so that there is no increase or decrease in bandwidth. The HIGH sign corresponds to a plus 5 volt voltage pulse, the LOW sign corresponds to a minus 5 volt voltage pulse, the NULL sign corresponds to a zero volt voltage state.

The coding rule for the channel coding according to the invention provides the following rules:

A HIGH sign in the DATA input signal is always encoded in a HIGH sign in the CHAN signal to be transmitted. A LOW character in the DATA input signal is always coded into a LOW character in the CHAN signal to be transmitted. However, if a LOW character in the DATA input signal is followed by another LOW character, this additional LOW character in the CHAN output signal is not encoded in another LOW character, but in a NULL character. The same applies to two consecutive HIGH characters in the DATA input signal. Here too, a HIGH sign immediately following a HIGH sign is coded by a NULL sign in the signal CHAN to be transmitted.

However, if the preceding character in the CHAN signal to be transmitted is a ZERO character, coding is carried out according to the basic coding presented above, so that a further LOW character in the DATA input signal is coded with a LOW character in the CHAN signal to be transmitted, or a following HIGH character in the DATA input signal is coded to a HIGH character in the CHAN signal to be transmitted.

Protection naturally also encompasses other coding variants. B. in principle, a LOW character in the input signal can be converted into a HIGH character in the signal to be transmitted.

With this type of coding, a change of state can always be generated on the transmission medium between two signal units. In any case, there is an edge between two bits. With any encoding covered by the protection, it must be ensured that a change of state takes place after each signal unit.

With this type of channel coding, the working cycle can be obtained in the receiving unit due to the regular changes in state in the signal to be transmitted without the aid of an additional oscillator. In contrast to Manchester coding, no time condition has to be observed.

The signal-to-noise ratio is not reduced by using this coding when using the ISO 11898 layer. At most there are steeper edges when changing from a HIGH sign to a LOW sign.

In summary, according to FIG. 1, a binary signal is encoded into a ternary signal while maintaining the bit times, taking into account the changes in state in the signal to be transmitted. The channel coding accordingly uses three characters / states on a transmission bus to represent two data characters / states. An overhead of log ₂ 3 = 1.58 = 36% is thus achieved in the value range. With a Manchester code, four states (2 bits) are required for the representation of two data states. Therefore, an overhead of log ₂ 4 = 2 = 50% is achieved in the time domain. FIG. 1b shows the signal CHAN belonging to the input signal DATA, to be transmitted, coded according to the above coding regulation.

FIG. 3 shows an arrangement according to the invention with two combined output and reception units 4, which are connected via a transmission medium 3, which in turn has two bus lines 31 and 32. The first output and reception unit 4 contains a microcontroller 13 with an interface 131, an encoder 11, a decoder 21 and two drivers 22. The drivers 22 are CAN drivers in the form of standard components that use cables and connectors standardized according to DIN ISO 11898 can. The drivers are connected antiparallel to one another and to the transmission medium 3. The CAN HIGH output of driver 12 (component A) and the CAN LOW output of further driver 12 (component B) are connected to first bus line 31. Likewise, the CAN-LOW output of the first driver 12 (component A) is connected to the CAN-LOW output of the second driver 12 (component B) with the second bus line 32. As a result of this interconnection of the drivers, the bus states HIGH, LOW and NULL can be generated between the bus lines.

FIG. 4 shows the two drivers 12 and their anti-parallel connection with one another. In this case, the input TXA is assigned to the first driver 12, the input TXB to the second driver 12. FIG. 6 shows a table from which, among other things, it can be seen how the inputs TXA and TXB of the driver 12 are to be assigned to the bus states LOW, ZERO and Get HIGH. For example, for a LOW bus state, TXA should be controlled with 1 and TXB with ZERO at the same time. Such an interconnection of the drivers is only permitted if it is excluded that the two drivers are not actively driving different potentials. According to table Figure 6, a state must be prevented in which both driver inputs TXA and TXB are not occupied. In the present example, PCA82C250 blocks from Philips are used as CAN drivers. there TX = 5 volts is the recessive state and TX = 0 volts is the dominant state.

FIG. 7 shows a signal transmitted on a bus, recorded after the course of the signal potentials on the individual bus lines 31 and 32. The differential voltage between these two bus lines supplies the signal level of the signal to be transmitted.

The driver modules 12 are controlled via the signals TXA and TXB by the coding unit 11, which implements the coding rule according to the invention. The data information to be transmitted is supplied as an input signal DATA by the microcontroller 13 to the coding unit 11 via its interface 131 (SPI = Serial Peripheral Interface). This SPI interface 131 makes it possible to read and output data synchronously via a data and clock line.

At the same time, the drivers 12 of a combined output and reception unit 4 function to receive signals transmitted on the transmission medium 3. These drivers 12 convert the received bus signals into signals RXA and RXB. The basis of this transformation process is again the state table according to FIG. 6 with regard to the outputs RXA and RXB of the drivers 12. The drivers 12 thus serve as CAN bus transceivers.

The signals RXA and RXB are fed to the coding unit 21. The received signals are decoded in the decoding unit 21 and fed to the microcontroller for further processing as the working signal DATA via the interface 131. Furthermore, a work cycle STROBE is derived from the received signals, which in turn is fed back to the coding unit 11.

The further combined output and reception unit 4 is constructed symmetrically and in turn contains micro- Controller 23 with interface 231, a coding unit 11, a decoding unit 21 and two drivers 22, all of whose functions have already been dealt with.

For example, the data transmission follows the following sequence: The microcontroller 13 sends an NRZ data sequence via the SPI interface 131. The coding unit 11 converts this into a so-called tri-state signal (TXA, TXB). The CAN bus transceivers / drivers 12 then use these to generate the corresponding bus states. The bus transceiver 12 of the further combined output and reception unit 4 receives the signal and converts it accordingly into the signals RXA and RXB. A decoding unit 21 of the receiver uses this to generate the working signal DATA, which should otherwise be the same as the input signal DATA, and the working clock strobe, which are fed to the microcontroller 23 via the SPI interface 231.

The decoding unit 21 is clocked by the controller 23. The clock must be more than twice the data rate. The clock rate has no upper limit.

Coding and decoding units 11 and 21 can be implemented as hardware or as software in a microcontroller.

The sequence described above can also be implemented by a state machine which follows the state table according to FIG. 9. Here, TX is the input signal of the coding unit 11 and thus corresponds to the input signal DATA. The signals TXA and TXB correspond to the sizes Q2 and Q1 in the table.

The following output equations can be obtained from this state table according to FIG. 9.

TxA = (NOT) Tx + Ql * (NOT) Q2; TxB = Tx + (N0T) Q1 * Q2; A conversion of these equations into a logic circuit is shown in FIG. 8.

Depending on the number of bits to be transmitted in succession and the date, it may happen that the coding unit 11 does not end with a ZERO character, but with a LOW character or a HIGH character. In the case of multiple access to the bus medium, the end bus state must be the idle state zero. There are several ways to ensure this: On the one hand, this end bus state can be achieved by a logical condition: If the number of bits of the same name last counted is odd, a pseudo bit of the same name is appended, through which the coding unit returns to the zero state. This function can be carried out either in the microcontroller or in the coding unit.

Alternatively, a time condition can be introduced: The coding unit sets the ZERO state if no state change has occurred after a certain time.

The decoding in the decoding unit can be done by software at slow transmission speeds in the range up to 10 kilobits per second. For higher transmission rates, the decoding unit must be implemented in hardware.

A state table of the decoding unit is shown in Figure 11.

The following output equation results from the status table:

D = (NOT) Q2 * (NOT) RxA * RxB + (NOT) RxA * RxB + (NOT) Ql * Q2 * RxA * RxB + D * Ql * Q2 * RxA * RxB;

The associated circuit is shown in Figure 10.

Claims

claims 1. unit for outputting a signal on a transmission channel in a motor vehicle, with a coding unit (11) for converting an input signal (DATA) into the signal to be output (CHAN) using a coding rule, in which the coding specification for the signal to be output provides for a character set of at least n + 1 characters if the character set for the input signal has n characters, - in which the coding specification for a signal unit of the input signal (DATA) occupied by a character provides a signal unit of the same duration (T) in the signal to be output (CHAN), and - In which the coding regulation for two successive signal units in the signal to be output (CHAN) provides different characters. 2. The unit of claim 1, wherein each character is represented by a discrete electrical signal state. 3. Unit according to claim 1 or claim 2, wherein the character set for the input signal (DATA) has two different characters and the character set for the signal to be output (CHAN) three characters. 4. Unit according to claim 3, in which the coding rule is designed such - that a low sign in the input signal (DATA) is always coded into a low sign or a high sign in the output signal (CHAN), that a high character in the input signal (DATA) is encoded in principle in a high character or a low character in the output signal (CHAN), - That a low character following a low character in the input signal (DATA) into a zero character in the output signal (CHAN) is coded, unless the previous character in the output signal (CHAN) was already a zero character, - That a high character following a high character in the input signal (DATA) is encoded into a zero character in the output signal (CHAN), unless the previous character in the output signal (CHAN) was already a zero character, and - That is encoded according to the basic coding, if the previous character in the output signal (CHAN) was a zero character. 5. Unit according to one of the preceding claims, with two of the coding unit (11) downstream driver modules (12) for connecting the unit (1) to the transmission channel (3), which are interconnected in anti-parallel. 6. unit for receiving a signal from a transmission channel in a motor vehicle, with a decoding unit (21) for converting the received signal (CHAN) into a working signal (DATA) using a decoding rule, in which the decoding rule for the working signal (DATA) provides for a character set of n characters if the character set for the received signal (CHAN) has more than n characters, - in which the decoding regulation for a signal unit occupied by a character of the received signal provides a signal unit with the same duration (T) in the working signal (DATA), and - With a unit for deriving a clock signal (STROBE) from the received signal (CHAN). 7. The unit of claim 6, wherein each character is represented by a discrete electrical signal state. 8. Unit according to claim 6 or claim 7, where the character set for the working signal (DATA) has two different characters and the character set for the received signal (CHAN) has three characters. 9. Unit according to claim 8, in which the decoding rule is designed in such a way - that e low character in the received signal (CHAN) is basically decoded in em low character or a high character in the working signal (DATA), that a high character in the received signal (CHAN) is basically decoded in a high character or a low character in the working signal (DATA), - That the character in the working signal, which is derived from a zero character in the received signal (CHAN), is the same as the previous character of the working signal (DATA). 10. Unit according to one of claims 6 to 9, with two driver modules (22) connected upstream of the decoding unit (21) for connecting the unit (2) to the transmission channel (3), which are connected in anti-parallel with one another. 11. Arrangement for data transmission in a motor vehicle via a transmission channel, - With a unit (1) for outputting a signal on the transmission channel (3), with a coding unit (11) for converting an input signal (DATA) into the signal to be output (CHAN) using a coding rule, in which the coding specification for the signal to be output (CHAN) provides for a character set of at least n + 1 characters if the character set for the input signal (DATA) contains n characters, - in which the coding rule for a signal unit of the input signal (DATA) with a character provides for a signal unit with the same duration (T) in the signal to be output (CHAN), in which the coding regulation provides for different characters for two successive signal units in the signal to be output (CHAN), with a unit (2) for receiving a signal (CHAN) transmitted via the channel (3), - With a decoding unit (21) for converting the received signal (CHAN) into a working signal (DATA) based on a decoding rule, and - With a unit for deriving a clock signal (STROBE) from the received signal (CHAN). 12. Method for data transmission in a motor vehicle, - With the em input signal (DATA), the signal to be transmitted (CHAN) is coded according to the following provisions: - A signal unit of the input signal (DATA) assigned a character corresponds to a signal unit with the same duration (T) in the signal to be transmitted (CHAN); - Characters of the input signal (DATA) from a character set of n characters are transcoded into characters of the signal to be transmitted (CHAN) from a character set of at least n + 1 characters; - Two successive signal units in the signal to be transmitted (CHAN) always have different characters; - In the em signal thus formed (CHAN) is transmitted to a receiving unit (2). 13. The method according to claim 12, in which in the receiving unit (2) an clock signal is derived from the transmitted signal (CHAN). 14. The method of claim 12 or claim 13, wherein each character is represented by a discrete electrical signal state. 15. The method according to any one of claims 12 to 14, wherein the character set for the input signal (DATA) comprises two different characters, and the character set for the signal to be transmitted (CHAN) three characters. 16. The method according to claim 15, - where a low character in the input signal (DATA) is always encoded in a low character or a high character in the output signal (CHAN), - in which an em high character in the input signal (DATA) is generally coded in an em high character or em low character in the output signal (CHAN), - where the low character following the low character in the input signal (DATA) is coded a zero character in the output signal (CHAN), unless the previous character in the output signal (CHAN) was already a zero character, - in which a high sign following the high sign in the input signal (DATA) in em zero sign in the output signal (CHAN) is encoded unless the previous character in the output signal (CHAN) was already a zero character, and - Which is coded in accordance with the basic coding if the previous character in the output signal (CHAN) was a zero character.