Communication device and method for improved synchronous data transmission

Disclosed is a method and device for transmitting data between at least two transmitters and a receiver which are connected to a bus. A synchronization signal is applied to the bus and a number of data volume counters corresponding to the number of transmitters reduced by one is set to a predefined initial value. A first transmitter transmits in the form of data elements a predefined data volume allocated to the transmitter over the bus to the receiver. The data volume values of the other transmitters are selected so that only one transmitter at any given time simultaneously transmits on the bus.

The invention relates to a method for transmitting data between at least two transmitters and at least one receiver, wherein the transmitters and the at least one receiver are connected to a bus. The invention further relates to a communication device with at least two transmitters connected to a bus and at least one receiver connected to a bus, wherein the transmitters always have at least one data source and a first bus interface connected thereto, and wherein at least the one receiver has a data sink and a second bus interface connected thereto.

Such a method and such a communication device are known in practice. The communication device is installed in a motor vehicle and has several transmitters, each of which has, as a data source, a sensor for detecting a physical quantity for measurement. By means of the sensors, measurements are read and stored in a data storage unit integrated in the transmitters. The measurements can be imported from the data storage unit and transmitted over a bus to a receiver configured as a control mechanism. For transmission of the measurements, the control mechanism first transmits a corresponding request to one of the sensors over the bus, whereupon the respective sensor transmits the data on the bus. The data are then imported from the bus to the control mechanism. The transmitters can also transmit on the bus without a previous request by the control mechanism. To this end, the communication device has an arbitration logic, which controls the data transmission over the bus. The purpose of the arbitration logic is to prevent several bus participants from transmitting on the bus at the same time and in turn prevent transmission errors. A disadvantage, however, resides in the communication device in that the arbitration logic in particular is quite expensive. A further disadvantage resides therein in that the individual bus participants (transmitters, receivers) require oscillators with long-term stability as timers. The latter, however, are relatively expensive.

Another communication device is also known in practice, which device has several transmitters, each of which is connected to a central control mechanism via its own data link. The individual transmitters continuously transmit data to the control mechanism via their individually allocated data links. The cost of the cabling, however, increases rather steeply as the number of sensors is increased. Furthermore, the control mechanism must have a correspondingly large number of input and/or output ports.

The object is therefore to develop a method and a communication device of the aforementioned type which enable, in a simple manner, data transmission between the transmitters and the at least one receiver.

This object is achieved for the method by the following procedural steps:a) Application of a synchronization signal to the bus and setting to a predefined initial value at least a number of data volume counters corresponding to the number of transmitters reduced by one,b) Carrying out the following steps for a first transmitter:b1) Transmission of a data element from the transmitter over the bus to at least the one receiver,b2) Determination of the transmitted data volume,b3) Comparison of the transmitted data volume with a predefined data volume allocated to the transmitter,b4) If the measured data volume is smaller than the predefined data volume: repetition of steps b1)-b4),c) Carrying out the following steps for each additional transmitter:c1) Reception of a data element from the bus,c2) Adjusting the counter reading of a data volume counter allocated to the respective transmitter according to the received data volume,c3) Comparison of the counter reading with a predefined data volume value allocated to the respective transmitter,c4) If the counter reading has not yet reached the predefined data volume value: repetition of steps c1)-c4),c5) Carrying out of steps b1)-b4),
wherein the data volume value of the other transmitter is chosen or the data volume values of the other transmitters are chosen so that at any given time only one transmitter is simultaneously transmitting on the bus.

In an advantageous manner, the data transmission thus takes place over the common bus or the common bus Sink in a sequence specified by the configuration of the transmitters. One after another, the individual transmitters thus keep transmitting data elements over the bus until a data volume specified for the respective transmitter is transmitted from the data source of the transmitter to the bus. Initially a first transmitter transmits its data on the bus. The transmitter that is next in line for data transmission only starts transmitting data if the transmitter in the process of transmitting on the bus has completed the transmission process. The time at which the individual transmitters start transmitting data is determined by the transmitters that transmit their data on the bus after the first transmitter, in each case by monitoring the bus and, on the basis of a synchronization signal, measuring the data volume transmitted over the bus and comparing it with a predefined data volume value allocated to the respective transmitter. As soon as said data volume value is reached, the respective transmitter starts transmitting data. A collision due to several transmitters simultaneously transmitting on the bus is thus avoided at the outset. Preference is given to cyclical data transmission over the bus, wherein additional data transmission cycles are carried out in like manner after the ending of a first data transmission cycle. The data transmission method of the invention is advantageously suited for application in a redundant system, for example, a position sensor for an adjustment element having a plurality of sensor elements. Such an adjustment element can in particular be a throttle valve or a gas pedal of a motor vehicle.

In a preferred embodiment of the invention, for at least two data elements the time interval for the transmission from the transmitter to the at least one receiver over the bus is different. In particular, this is achievable through representation of a data element with an information content of several bits by a bus signal having at least a first signal level and at least a second signal level, wherein the duration of at least one of said signal levels is a function of the information stored in the data element.

In an advantageous embodiment of the invention, at least one transmitter checks the plausibility of the data elements transmitted over the bus and emits a status signal, which is based on the result of this check, on the bus. The status signal can then be imported by the other bus participants (transmitters, receivers), in order to discard, should the need arise, the data imported into the receiver from the bus in the event of an error and to retransmit the data in which the transmission error occurred from the transmitters over the bus to the receiver. Preference is given to transmission of the status signal on the bus after the end of a data transmission cycle. A data transmission cycle is to be understood as the time interval between the application of the synchronization signal to the bus and the point in time when all of the transmitters connected to the bus have transmitted their allocated data volumes on the bus.

Preference is given to determining, for at least one transmitter, the length of time during which the respective transmitter is in line for transmission of its data elements on the bus, wherein the measured length of time is compared with a threshold value, and wherein another transmitter carries out the steps b1)-b4) mentioned in claim1in the event that the measured length of time corresponds to and/or is greater than the threshold value. Data transmission over the bus is thus still possible should a transmitter fail and/or malfunction.

The aforesaid object is achieved for the communication device of the aforementioned type wherein a provision is made for a mechanism for transmitting a synchronization signal on the bus, wherein the first bus interfaces always have a transmitter mechanism connected to the bus, a receiver mechanism connected to the bus and to a control mechanism, a measuring device connected to said receiver mechanism and comprising a data volume counter for measuring the volume of data transmitted over the bus, and a comparator connected to said measuring device and to said control mechanism for comparing the counter reading of the data volume counter with at least one predefined data volume value, wherein the control mechanism of a first transmitter is control-connected to the receiver mechanism and to the transmitter mechanism of said first transmitter so that, after receiving the synchronization signal, data of a predefined first data volume are transmitted on the bus from the data source of the first transmitter by means of the transmitter mechanism, wherein the control mechanism of at least a second transmitter is control-connected to the transmitter mechanism of said second transmitter so that, after receiving a predefined second data volume allocated to the respective second transmitter, data of a predefined third data volume are transmitted on the bus from the data source of the respective second transmitter by means of its transmitter mechanism, and wherein the first data volume, at least a second data volume, and at least a third data volume are selected so that at any given time only one transmitter simultaneously transmits on the bus.

The access to the common bus takes place cyclically, according to a sequence defined by the configuration of the transmitters, wherein the individual senders sequentially transmit data over the bus to at least the one receiver. In a simple manner, the communication device avoids a collision on the bus. The receiver apparently receives the data from just one element. The underlying bus structure is not visible to the receiver. For the receiver, this leads to considerable simplification of the data analysis.

ft is advantageous if the communication device has a mechanism for transmitting a cycle length signal on the bus, if the transmitters always have a timer for generating a timer signal connected to the transmitter mechanism, if at least one timer has an adjustment mechanism for setting the cycle length of its timer signal, and if the adjustment mechanism is control-connected to the receiver mechanism of the respective transmitter so that the cycle length of the timer signal is adjustable as a function of the length of the cycle length signal. The timers of the individual transmitters can then easily adjust their cycle lengths according to the cycle length signal so that the timers of all transmitters connected to the bus then work in synchronization with each other. Because the cycle length signal is cyclically transmissible on the bus, the timers do not require long-term stability. It is thus possible to manufacture the timers easily and economically. Preference is given to integration of the mechanism for transmitting the cycle length signal in one of the transmitters. This transmitter can serve as the master transmitter and, should the need arise, also transmit the synchronization signal on the bus.

In a preferred embodiment of the invention, the data source has at least one sensor for detecting a measurement signal. Such a sensor can be a magnetic field sensor, particularly a Hall effect sensor.

The transmitter mechanism advantageously comprises a pulse width modulator with which a data signal having at least one first data signal section having a first signal level and one second data signal section having a second signal level can be generated, and wherein the length of at least one of said data signal sections is a function of information stored in the data signal. Independently of the information stored therein, the data signals generated as a function of the data elements to be transmitted over the bus can then have at any given time only two signal levels or one slope, thereby resulting in a corresponding reduction of the incidence of EMV interferences in the data transmission.

It is advantageous if at least one transmitter has a mechanism for checking the plausibility of the data received from the bus and if preference is given to said mechanism for checking the plausibility being control-connected to the transmitter mechanism so that a status signal based on the result of the plausibility check is emittable on the bus. Should an error in the data transmission be ascertained, the corresponding data can be discarded, should the need arise. Furthermore, there is the possibility of retransmitting the data in which the transmission error was ascertained over the bus.

In a preferred embodiment of the invention, at least one transmitter has a measuring device for determining the length of the time during which another transmitter is in line for transmission of data on the bus, wherein said measuring device is connected to a comparator for comparing the length of time with a threshold value, and wherein said comparator is control-connected to the transmitter mechanism of said first-mentioned transmitter so that in the event the measured length of time corresponds to and/or is greater than the threshold value, data of the predefined data volume allocated to the first-mentioned transmitter are transmitted from the data source of said transmitter on the bus by means of the transmitter mechanism. Particularly stable data transmission over the bus to the receiver is enabled by this measure.

A communication device designated in its entirety by 1 inFIG. 1has a bus2to which a plurality of transmitters3a,3band a receiver4are connected. For communication over the bus2the transmitters3a,3bin each case have a first bus interface and the receiver4has a second bus interface. It can be discerned inFIGS. 2 and 3that the first bus interfaces in each case comprise a transmitter mechanism5a,5band a first receiver mechanism6a,6b. The receiver4has a second receiver mechanism7. The transmitter mechanisms5a,5b, the first receiver mechanisms6a,6b, and the second receiver mechanism7are in each case connected to the bus2.

Each transmitter3a,3balways has a data source8a,8b, which has a sensor, which is not shown in any greater detail in the drawing, for detecting a digital measurement signal. The data source8a,8bis always connected via a first control mechanism9a,9bto the transmitter mechanisms5a,5bof the respective transmitter3a,3b. Furthermore, each transmitter3a,3bhas a timer10a,10b, which is connected to the first control mechanism9a,9b. Furthermore, the first control mechanism9a,9bof each transmitter3a,3bis always connected to the first receiver mechanism6a,6bof the respective transmitter3a,3b.

It can be discerned inFIG. 4that the receiver4has a data sink11. The latter may comprise, for example, a data storage unit in which digital measurement signals or measurement values from the individual data sources8a,8btransmitted over the bus2can be stored. The data sink11is connected to the second receiver mechanism7via a second control mechanism12. Furthermore, the second control mechanism12is connected to a timer10callocated to the receiver4.

The transmitter3aacts as a master and has a mechanism for generating a master timer signal, which is formed by frequency division from an output signal of the timer10a. The master timer signal can be transmitted on the bus in the form of a synchronization signal14by means of the transmitter mechanism5aof the transmitter3a. During the transmission of the synchronization signal14, the bus is set to a predefined signal level for a time interval lasting for a predefined number of timer cycles of the master timer signal.

The sensors3bare configured as slaves and in each case have a timer synchronization mechanism13a, which is connected to the timer10band the receiver mechanism6bof the respective sensor3b. By means of the timer synchronization mechanism13a, when the synchronization signal14occurs, a timer signal generated in the respective sensor3bby frequency division from an output signal of the timer10bis synchronized in terms of frequency and phasing.

In like manner the receiver4is configured with a timer synchronization mechanism13b, which is connected to the timer10cand the second receiving mechanism7. By means of the timer synchronization mechanism13b, when the synchronization signal14occurs, a timer signal generated in the receiver4by frequency division from an output signal of the timer10cis synchronized to the master timer signal of the sensor3ain terms of frequency and phasing.

So that the individual transmitters3a,3bcan jointly use the bus to transmit data from the data sources8a,8bto the data sink11without a collision occurring during the data transmission, the transmitters3bconfigured as slaves always have at least a measurement mechanism15with a data volume counter for measuring the volume of the data transmitted over the bus.

The measurement mechanism15is always connected via a comparator17to the control mechanism9bof the transmitter3bfor comparison of the counter reading of the data volume counter with a predefined data volume value16allocated to the respective transmitter3b.

As can be discerned with the aid of the timing diagram inFIG. 5, at the beginning of a data transmission cycle, the transmitter3aconfigured as a master first transmits the synchronization signal14on the bus2. The synchronization signal14is received by the transmitters3bconfigured as slaves and the receiver4, whereupon the latter in each case synchronize their timer signals generated from the output signal of the timer10bor10cwith the master signal of the transmitter3a. Upon receipt of the synchronization signal14, the transmitters3balways set the counter reading of their respective data volume counters to a predefined initial value, the value of which can be, for example, zero.

Following the synchronization signal14, the transmitter3a, henceforth also designated as the first transmitter3a, transmits the data furnished by its data source8aon the bus2. The corresponding data signal is designated by18inFIG. 5. The data have a predefined first data quantity or a predefined first data volume. The data are transmitted on the bus as data elements, which can contain, for example, 4 bits of information in each case.

A first section of each data element has a first signal level and a second section a second signal level, respectively. The first section has a fixed time interval and the second section has a time interval that varies as a function of the information allocated to the data element and to be transmitted over the bus, with said time interval corresponding to the first time interval or a multiple thereof, depending on the information.

After each transmission of a data element, the first transmitter3aalways measures the data volume that it transmitted on the bus and compares it with the predefined data volume allocated to the first transmitter3a, If the measured data volume is smaller than the predefined data volume, the aforementioned steps are repeated, i.e., the first transmitter3atransmits another data element on the bus2, in order to check again if the predefined date volume was transmitted. This process is repeated until the predefined data volume has been transmitted on the bus.

While the first transmitter3ais transmitting data elements on the bus2, the remaining transmitters3band the receiver4import the data elements from the bus. In doing so, the importation of the data elements is synchronized by means of the timer signal of the respective transmitter3bor the receiver4. After each importation of a data element, at least those transmitters3bwhich still have not transmitted any data elements on the bus2adjust the counter readings of their data volume counters according to the received data volume and compare them to a predefined data volume value allocated to one of the respective sensors3b.

If the comparison indicates that the counter reading has not yet reached the predefined data volume value, the process is always repeated, i.e., another data element is imported from the bus2, the data volume counter is adjusted accordingly, and the counter reading is compared again with the predefined data volume value. Once the counter reading of a transmitter3bhas reached the predefined data volume value, said transmitter begins to transmit its allocated, predefined data volume on the bus2.

The data volume value of a second transmitter3bcorresponds to the data volume transmitted by the first transmitter3a, so that the second transmitter3bbegins transmitting data on the bus2as soon as the first transmitter3ahas transmitted its allocated data volume on the bus2. The data signal of the second transmitter3bis designated by19inFIG. 5.

In like manner the data volume value of a third transmitter3bcorresponds to the sum of the data volumes transmitted by the first transmitter3aand the second transmitter3b, so that the third transmitter3bbegins to transmit data on the bus2as soon as the second transmitter3bhas transmitted its allocated data volume on the bus2. The data signal of the third transmitter3bis designated by20inFIG. 5.

Should the need arise, in like manner other transmitters3bconnected to the bus can transmit data over the bus2. The individual transmitters3a,3bthus transmit their data over the bus2to the receiver4after one another, in a set sequence.

The transmitter3aacting as a master and at least another transmitter3breceive, when they themselves are not in the process of transmitting, the data elements transmitted over the bus2and check them for plausibility. Depending on the result of this check, after the end of each data transmission cycle the respective transmitters3a,3btransmit, always in sequence, status information in the form of, for example, a diagnosis bit, on the bus2. The corresponding status signal is designated by21inFIG. 5. In the plausibility check, the data elements can be compared, for example, to a predefined, admissible data array.

In the method for transmitting data between at least two transmitters3a,3band a receiver4, wherein the transmitters3a,3band the receiver4are connected to a bus2, a synchronization signal is therefore applied to the bus2and a number of data volume counters, which corresponds to the number of transmitters3a,3breduced by one, is set to a predefined initial value. A first transmitter3atransmits a predefined data volume allocated to the transmitter in the form of data elements to the receiver4over the bus. For each additional transmitter3b,3athe following steps are carried out:

1) Reception of a data element from the bus2,

2) Adjusting the counter reading of a data volume counter allocated to the respective transmitter3b,3aaccording to the received data volume,

3) Comparison of the counter reading with a predefined data volume value allocated to the respective transmitter3b,3a,

4) In the event the counter reading has not yet reached the predefined data volume value: repetition of steps 1)-4),

5) Transmission of data elements of a predefined data volume allocated to the respective transmitter3b,3aover the bus to the receiver4.

The data volume value of the other transmitter3b,3ais selected or the data volume values of the other transmitters3b,3aare selected in such a way that at any given time only one transmitter3a,3bsimultaneously transmits on the bus2.