COMMUNICATION DEVICE AND METHOD FOR DATA TRANSMISSION
[0001] 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.
[0002] 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.
[0003] 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.

[0004] 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.
[0005] 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:
d) 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 Cl) - 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.
[0006] In an advantageous manner, the data transmission thus takes place over
the common bus or the common bus link 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.
[0007] 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.
[0008] 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.
[0009] 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 claim 1 in 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.

[0010] 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.
[0011] 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.
[0012] It 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.

[0017] An illustrative embodiment of the invention is explained in more detail in the
following, with reference to the drawing, wherein:
[0018] Fig. 1 shows a schematic illustration of a communication device having a
plurality of transmitters and one receiver, which are connected with each other via a
data bus,
[0019] Fig. 2 shows a block diagram of a first transmitter acting as a master
transmitter,
[0020] Fig. 3 shows a block diagram of a second transmitter configured as a slave
transmitter,
[0021] Fig. 4 shows a block diagram of the receiver, and
[0022] Fig. 5 shows a schematic illustration of signals transmitted over the bus.
[0023] A communication device designated in its entirety by-1 in Fig. 1 has a bus 2
to which a plurality of transmitters 3a, 3b and a receiver 4 are connected. For
communication over the bus 2 the transmitters 3a, 3b in each case have a first bus
interface and the receiver 4 has a second bus interface. It can be discerned in Figs. 2
and 3 that the first bus interfaces in each case comprise a transmitter mechanism 5a,
5b and a first receiver mechanism 6a, 6b. The receiver 4 has a second receiver
mechanism 7. The transmitter mechanisms 5a, 5b, the first receiver mechanisms 6a,
6b, and the second receiver mechanism 7 are in each case connected to the bus 2.
[0024] Each transmitter 3a, 3b always has a data source 8a, 8b, which has a
sensor, which is not shown in any greater detail in the drawing, for detecting a digital
measurement signal. The data source 8a, 8b is always connected via a first control
mechanism 9a, 9b to the transmitter mechanisms 5a, 5b of the respective transmitter
3a, 3b. Furthermore, each transmitter 3a, 3b has a timer 10a, 10b, which is
connected to the first control mechanism 9a, 9b. Furthermore, the first control
mechanism 9a, 9b of each transmitter 3a, 3b is always connected to the first receiver
mechanism 6a, 6b of the respective transmitter 3a, 3b.
[0025] It can be discerned in Fig. 4 that the receiver 4 has a data sink 11. The
latter may comprise, for example, a data storage unit in which digital measurement
signals or measurement values from the individual data sources 8a, 8b transmitted
over the bus 2 can be stored. The data sink 11 is connected to the second receiver
mechanism 7 via a second control mechanism 12. Furthermore, the second control
mechanism 12 is connected to a timer 10c allocated to the receiver 4.
[0026] The transmitter 3a acts 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 timer 10a. The master timer signal can be transmitted on the bus in the form of a
synchronization signal 14 by means of the transmitter mechanism 5a of the

transmitter 3a. During the transmission of the synchronization signal 14, 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.
[0027] The sensors 3b are configured as slaves and in each case have a timer
synchronization mechanism 13a, which is connected to the timer 10b and the
receiver mechanism 6b of the respective sensor 3b. By means of the timer
synchronization mechanism 13a, when the synchronization signal 14 occurs, a timer
signal generated in the respective sensor 3b by frequency division from an output
signal of the timer 10b is synchronized in terms of frequency and phasing.
[0028] In like manner the receiver 4 is configured with a timer synchronization
mechanism 13b, which is connected to the timer 10c and the second receiving
mechanism 7. By means of the timer synchronization mechanism 13b, when the
synchronization signal 14 occurs, a timer signal generated in the receiver 4 by
frequency division from an output signal of the timer 10c is synchronized to the
master timer signal of the sensor 3a in terms of frequency and phasing.
[0029] So that the individual transmitters 3a, 3b can jointly use the bus to transmit
data from the data sources 8a, 8b to the data sink 11 without a collision occurring
during the data transmission, the transmitters 3b configured as slaves always have at
least a measurement mechanism 15 with a data volume counter for measuring the
volume of the data transmitted over the bus.
[0030] The measurement mechanism 15 is always connected via a comparator 17
to the control mechanism 9b of the transmitter 3b for comparison of the counter
reading of the data volume counter with a predefined data volume value 16 allocated
to the respective transmitter 3b.
[0031] As can be discerned with the aid of the timing diagram in Fig. 5, at the
beginning of a data transmission cycle, the transmitter 3a configured as a master first
transmits the synchronization signal 14 on the bus 2. The synchronization signal 14
is received by the transmitters 3b configured as slaves and the receiver 4,
whereupon the latter in each case synchronize their timer signals generated from the
output signal of the timer 10b or 10c with the master signal of the transmitter 3a.
Upon receipt of the synchronization signal 14, the transmitters 3b always set the
counter reading of their respective data volume counters to a predefined initial value,
the value of which can be, for example, zero.
[0032] Following the synchronization signal 14, the transmitter 3a, henceforth also
designated as the first transmitter 3a, transmits the data furnished by its data source
8a on the bus 2. The corresponding data signal is designated by 18 in Fig. 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.
[0033] 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.
[0034] After each transmission of a data element, the first transmitter 3a always
measures the data volume that it transmitted on the bus and compares it with the
predefined data volume allocated to the first transmitter 3a. If the measured data
volume is smaller than the predefined data volume, the aforementioned steps are
repeated, i.e., the first transmitter 3a transmits another data element on the bus 2, 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.
[0035] While the first transmitter 3a is transmitting data elements on the bus 2, the
remaining transmitters 3b and the receiver 4 import 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 transmitter 3b or the receiver 4. After each importation
of a data element, at least those transmitters 3b which still have not transmitted any
data elements on the bus 2 adjust 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 sensors 3b.
[0036] 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 bus 2, 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 transmitter 3b has reached the predefined data
volume value, said transmitter begins to transmit its allocated, predefined data
volume on the bus 2.
[0037] The data volume value of a second transmitter 3b corresponds to the data
volume transmitted by the first transmitter 3a, so that the second transmitter 3b
begins transmitting data on the bus 2 as soon as the first transmitter 3a has
transmitted its allocated data volume on the bus 2. The data signal of the second
transmitter 3b is designated by 19 in Fig. 5.
[0038] In like manner the data volume value of a third transmitter 3b corresponds
to the sum of the data volumes transmitted by the first transmitter 3a and the second

transmitter 3b, so that the third transmitter 3b begins to transmit data on the bus 2 as
soon as the second transmitter 3b has transmitted its allocated data volume on the
bus 2. The data signal of the third transmitter 3b is designated by 20 in Fig. 5.
[0039] Should the need arise, in like manner other transmitters 3b connected to
the bus can transmit data over the bus 2. The individual transmitters 3a, 3b thus
transmit their data over the bus 2 to the receiver 4 after one another, in a set
sequence.
[0040] The transmitter 3a acting as a master and at least another transmitter 3b
receive, when they themselves are not in the process of transmitting, the data
elements transmitted over the bus 2 and check them for plausibility. Depending on
the result of this check, after the end of each data transmission cycle the respective
transmitters 3a, 3b transmit, always in sequence, status information in the form of, for
example, a diagnosis bit, on the bus 2. The corresponding status signal is designated
by 21 in Fig. 5. In the plausibility check, the data elements can be compared, for
example, to a predefined, admissible data array.
[0041] In the method for transmitting data between at least two transmitters 3a, 3b
and a receiver 4, wherein the transmitters 3a, 3b and the receiver 4 are connected to
a bus 2, a synchronization signal is therefore applied to the bus 2 and a number of
data volume counters, which corresponds to the number of transmitters 3a, 3b
reduced by one, is set to a predefined initial value. A first transmitter 3a transmits a
predefined data volume allocated to the transmitter in the form of data elements to
the receiver 4 over the bus. For each additional transmitter 3b, 3a the following steps
are carried out:
1) Reception of a data element from the bus 2,
2) Adjusting the counter reading of a data volume counter allocated to the
respective transmitter 3b, 3a according to the received data volume,
3) Comparison of the counter reading with a predefined data volume value allocated
to the respective transmitter 3b. 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 transmitter 3b, 3a over the bus to the receiver 4.
The data volume value of the other transmitter 3b, 3a is selected or the data volume
values of the other transmitters 3b, 3a are selected in such a way that at any given
time only one transmitter 3a, 3b simultaneously transmits on the bus 2.

Claims
1. Method for transmission of data between at least two transmitters (3a, 3b) and at
least one receiver (4), wherein the transmitters (3a, 3b) and the at least one receiver
(4) are connected to a bus (2), comprising at least the following steps:
a) Application of a synchronization signal (14) to the bus (2) and setting at least a
number of data volume counters corresponding to the number of transmitters (3a,
3b) reduced by one to a predefined initial value,
b) For a first transmitter (3a, 3b), carrying out the following steps:
b1) Transmission of a data element from the transmitter (3a, 3b) to at least the
one receiver (4) over the bus (2),
b2) Determination of the transmitted data volume,
b3) Comparison of the transmitted data volume with a predefined data volume
allocated to the transmitter (3a, 3b),
b4) If the measured data volume is less than the predefined data volume:
repetition of steps b1) - b4),
c) For each additional transmitter (3b, 3a), carrying out the following steps:
d) Reception of a data element from the bus (2),
c2) Adjusting the counter reading of a data volume counter allocated to the
respective transmitter (3a, 3b) according to the received data volume,
c3) Comparison of the counter reading with a predefined data volume value
allocated to the respective transmitter (3b, 3a),
c4) In the event the counter reading has not yet reached the predefined data
volume value: repetition of steps d) - c4),
c5) Carrying out the steps b1) - b4) for the respective transmitter (3b, 3a),
wherein the data volume value of the other transmitter (3b, 3a) is selected or the data
volume values of the other transmitters (3b, 3a) are selected so that at any given
time only one transmitter (3a, 3b) simultaneously transmits on the bus (2).
2. Method as in claim 1, characterized in that, with at least two data elements, the
time interval for the transmission from the transmitter (3a, 3b) over the bus (2) to at
least the one receiver (4) is different.
3. Method as in claim 1 or 2, characterized in that at least one transmitter (3a, 3b)
checks the plausibility of the data elements transmitted over the bus, and a status
signal (21) based on the result of this check is emitted on the bus.

4. Method as in any one of claims 1 through 3, characterized in that for at least one
transmitter (3a, 3b), the length of time during which the respective transmitter (3a, 3b)
is in line for transmission of its data elements on the bus (2) is specified, that the
measured length of time is compared with a threshold value, and that in the event
that the measured length of time corresponds to and/or is greater than the threshold
value, another transmitter (3b) carries out the steps b1) - b4) mentioned in claim 1.
5. Communication device (1) with at least two transmitters (3a, 3b) connected to a
bus (2) and at least one receiver (4) connected to the bus (2), wherein the
transmitters (3a, 3b) always have at least one data source (8a, 8b) and a first bus
interface connected thereto, wherein the at least one receiver (4) has a data sink (11)
and a second bus interface connected thereto, wherein a mechanism for
transmission of a synchronization signal on the bus (2) is provided, wherein the first
bus interfaces always have a transmitter mechanism (5a, 5b) connected to the bus
(2), a receiver mechanism (6a, 6b) connected to the bus (2) and to a control
mechanism (9a, 9b), a measurement device (15) connected to said receiver
mechanism and having a data volume counter for measuring the volume of the data
transmitted over the bus (2), and a comparator (17) connected to the measurement
device (15) and to the control mechanism (9a, 9b) for comparing the counter reading
of the data volume counter with at least one predefined data volume value (16),
wherein the control mechanism (9a, 9b) of a first transmitter (3a) is control-connected
with the receiver mechanism (6a) and the transmitter mechanism (5a) of said
transmitter so that, after receiving the synchronization signal (14), data of a
predefined first data volume are transmitted on the bus (2) by means of the
transmitter mechanism (5a) from the data source (8a) of the first transmitter (3a),
wherein the control mechanism (9b) of at least a second transmitter (3b) is control-
connected with the transmitter mechanism (5b) of said transmitter so that, after
receipt of a predefined second data volume allocated to the respective second
sensor (3b), data of a predefined third data volume are transmitted on the bus (2) by
means of its transmitter mechanism (5b) from the data source (8b) of the respective
second transmitter (3b), 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 (3a, 3b) simultaneously transmits on the bus (2).
6. Communication device (1) as in claim 5, characterized in that it has a mechanism
for sending a cycle length signal on the bus (2), that the transmitters (3a, 3b) always
have a timer (10a, 10b) connected to the transmitter mechanism (5a, 5b) for

generating a timer signal, that at least one timer (10a, 10b) has a setting mechanism
for setting the cycle length of its timer signal, and that the setting mechanism is
control-connected to the receiver mechanism (6a, 6b) of the respective transmitter
(3a, 3b) so that the cycle length of the timer signal is settable as a function of the
duration of the cycle length signal.
7. Communication device (1) as in claim 5 or 6, characterized in that the data
source (8a, 8b) has at least one sensor for detecting a measurement signal.
8. Communication device (1) as in any one of claims 5 through 7, characterized in
that the transmitter mechanism (5a, 5b) has a pulse width modulator, by means of
which a data signal having at least one first data signal section having a first signal
level and a second data signal section having a second signal level can be generated,
and that the length of at least one of said data signal sections is a function of
information stored in the data signal.
9. Communication device (1) as in any one of claims 5 through 8, characterized in
that at least one transmitter (3a, 3b) has a mechanism for checking the plausibility of
the data received by the bus and that preference is given to the mechanism for
checking the plausibility being control-connected to the transmitter mechanism (5a,
5b) of the transmitter (3a, 3b) in such a way that a status signal (21) based on the
result of the plausibility check is emittable on the bus (2).
10. Communication device (1) as in any one of claims 5 through 9, characterized in
that at least one transmitter (3b) has a measurement device for determining the
length of time during which another transmitter (3a, 3b) is in line for transmission of
data on the bus, that the measurement device is connected to a comparator for
comparing the length of time with a threshold value, and that the comparator is
control-connected to the transmitter mechanism (5b) of the first-mentioned
transmitter (3b) 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 (3b) are transmitted from the data source
(8b) of said transmitter (3b) on the bus (2) by means of the transmitter mechanism
(5b).

In a method for transmitting data between at least two transmitters (3a, 3b) and a
receiver (4), wherein the transmitters (3a, 3b) and the receiver (4) are connected to a
bus (2), a synchronization signal is applied to the bus (2) and a number of data
volume counters corresponding to the number of transmitters (3a, 3b) reduced by
one is set to a predefined initial value. A first transmitter (3a) transmits in the form of
data elements a predefined data volume allocated to the transmitter over the bus to
the receiver (4). For each additional transmitter (3b, 3a), the following steps are
carried out:
1) Receipt of a data element from the bus (2),
2) Adjusting the counter reading of a data volume counter allocated to the respective
transmitter (3b, 3a) according to the received data volume,
3) Comparison of the counter reading with a predefined data volume value allocated
to the respective transmitter (3b, 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 transmitter (3b, 3a) over the bus to the receiver (4).
The data volume value of the other transmitter (3b, 3a) is selected or the data volume
values of the other transmitters (3b, 3a) are selected so that only one transmitter (3a,
3b) at any given time simultaneously transmits on the bus (2).