METHOD, SYSTEM AND GATEWAY FOR NETWORKING TIME-SENSITIVE FIELDBUSES

Description

Field of the invention

[0001] The invention relates to time-sensitive fieldbus systems, in particular to industrial fieldbus systems for controlling industrial systems. In particular, the invention relates to a method, a system, and a gateway for networking at least two time-sensitive fieldbuses. Background of the invention

[0002] Fieldbuses are used to connect various participant devices (e.g., field devices such as sensors, actuators, measuring probes, final control elements, etc., as well as controllers such as control or automation devices, programmable logic controllers, PLCs, etc.) in a system (e.g., an industrial production plant, vehicle, building, etc.) for the purpose of communication. Communication takes place particularly, but not exclusively, between various field devices and a fieldbus controller, which controls and monitors the processes taking place in the system. A participant device can be a field device or a controller and, in particular, has an interface with the fieldbus.

[0003] The messages to be transmitted over a fieldbus (e.g., data blocks, data streams) are at least partially time-sensitive, meaning they have real-time requirements regarding transmission latency. For example, such time-sensitive data requires that a message sent by a subscriber device be reliably received by the fieldbus controller or another field device connected to the fieldbus within a predictable time period.

[0004] The data to be transmitted between fieldbus nodes includes not only value communication, such as measured values, control values, or instructions, but also event communication for the temporal coordination of machines and system components. For example, the coordination and synchronization of machine component movements is increasingly no longer carried out via mechanical devices (e.g., metal presses with rigidly coupled insertion and removal devices in the machine cycle, camshafts, gears, etc.), but via digital messages transmitted via fieldbuses with real-time requirements.

[0005] A fieldbus is assigned to a time domain in which all participant devices each have a timer (e.g. a clock). The timers of the participant devices are synchronized with each other within the time domain and thus have a common understanding of time. This means that all participant devices of a fieldbus can follow a defined fieldbus communication cycle and are coordinated with each other to carry out the appropriate actions at the right time. A participant device of the fieldbus acts as the master for the time domain, with the master's timer providing the time reference for the other participant devices in the time domain. The latter participant devices, which derive their time from the master within the time domain, are also referred to as slaves. The role of the time master in the fieldbus can be assumed by a fieldbus controller or by another participant device connected to the fieldbus.The fieldbus time master can synchronize its time base with another time base, for example, with the time master of another fieldbus or with a hierarchically superior time base. By synchronizing the masters of multiple fieldbuses with each other, a time domain can also encompass multiple fieldbuses. While synchronizing the time base aligns the "clocks," this does not necessarily mean that two fieldbuses within a time domain have the same communication cycles.

[0006] The first generation of fieldbuses was developed to replace the previously common parallel wiring of machine components using cable harnesses with digital transmission technology. Several, partly proprietary, fieldbus protocols were developed for this purpose. Later generations of fieldbuses are primarily based on the IEEE 802.3 Ethernet standard, with the Ethernet protocols being modified or extended to implement time-sensitive networks (TSNs).

[0007] Standards for real-time Ethernet protocols are being developed, for example, by the IEEE 802.1Q Task Group for TSN networks. A real-time scheduler (time-aware scheduler) is defined, for example, by the IEEE 802.1QBv standard. The scheduler enables communication within a network to be divided into fixed, periodically repeating communication cycles and, within these cycles, to define, reserve, or negotiate fixed time slots for the transmission of time-critical data. This enables clocked end-to-end transmission between two subscriber devices.

[0008] Outside of the time slots designated for real-time transmission, non-time-sensitive data (best-effort data) can be transmitted using the well-known protocols for packet-switched transmission (e.g., Ethernet protocol). The real-time-supporting scheduler can establish guard bands to prevent the transmission of non-time-sensitive data packets from overlapping with the time slots reserved for real-time transmission.

[0009] Document US 2016 / 080533 A1 discloses a gateway that can transmit data between two networks of a vehicle. The first network is a time-sensitive FlexRay network and the second network is a vehicle Ethernet network.

[0010] Furthermore, TSN networks allow the transmission of non-time-sensitive data packets to be interrupted during real-time intervals and then resumed. This enables the coexistence of time-sensitive and non-time-sensitive communication in a TSN-capable network.

[0011] With the increasing digitalization and networking of systems (e.g., an entire production site), there is a need to enable communication between fieldbuses as well as communication between a fieldbus and devices at a higher-level control level, process control level, operational control level, and / or corporate level. Networking affects both non-time-sensitive data and time-sensitive data.

[0012] Although most real-time protocols for fieldbuses in use today are based on Ethernet, despite this commonality, technical differences exist that make different fieldbus types incompatible or not fully compatible with each other. It may also happen that different generations of fieldbuses are used, for example, when parts of a plant are added, replaced, or modernized; however, fieldbuses of different generations are not necessarily fully compatible. Efforts are currently underway to specify universally applicable real-time protocols that will replace the many proprietary and mutually incompatible protocols for time-sensitive fieldbuses. However, their use will require the replacement or upgrade of existing fieldbus systems, which is often not economically viable.

[0013] Existing solutions for time-sensitive communication between two or more fieldbuses assume that all connected fieldbuses have a uniform understanding of time, while also synchronizing all time offsets, durations, and / or start times of the fieldbus communication cycles. However, fieldbuses are often extensively configured at the beginning of a production process so that the machines and / or system components controlled by the fieldbus are optimally coordinated. However, adapting the cycle times of an existing fieldbus to newly added system components with additional fieldbuses would require reconfiguration of the existing processes controlled by the fieldbus.

[0014] There is therefore a need to network time-sensitive fieldbuses that are not fully compatible with each other. Summary of the invention

[0015] The object is achieved in particular by a method for networking a first time-sensitive fieldbus with a second time-sensitive fieldbus according to claim 1, by a system for networking at least two time-sensitive fieldbuses according to claim 17 and by a gateway for networking at least two time-sensitive fieldbuses according to claim 11.

[0016] To solve this problem, a gateway is used that mediates communication between time-sensitive fieldbuses. Since the gateway supports the respective time domains of all connected fieldbuses, the fieldbuses can communicate with each other largely without aligning the time domains and, in particular, the communication cycle times defined within the fieldbuses. This applies to both time-sensitive and non-time-sensitive data.

[0017] One aspect of the present invention relates to a method for networking a first time-sensitive fieldbus with a second time-sensitive fieldbus. The first time-sensitive fieldbus comprises a first subscriber device and has its own first time domain. The second time-sensitive fieldbus comprises a second subscriber device and has its own second time domain. The first time domain and the second time domain are frequency-synchronized. The first and the second fieldbus are connected to one another by means of a gateway for data transmission. The method comprises the gateway determining a first cycle time duration of the first time domain and a second cycle time duration of the second time domain at a reference time, and the gateway determining a time offset between the first time domain and the second time domain at the reference time.

[0018] Frequency synchronization can be achieved by synchronizing the clock frequencies in the time domains of the first and second fieldbus. With this type of frequency synchronization, the first and second fieldbus or the first and second time domains can have differently defined times, but the time offset is time-invariant, i.e. constant over time. By synchronizing only the frequencies in the first and second time domains, the time regimes in the fieldbuses can remain largely untouched. In particular, a hard time jump, which could otherwise occur when the first and second fieldbus times are aligned, is avoided in one or both fieldbuses. The alignment of the frequencies can take place over a period of time that does not impair the operation of the processes running in the fieldbuses.

[0019] By determining the first cycle time of the first time domain and the second cycle time of the second time domain at a reference time, as well as by determining a time offset between the first time domain and the second time domain at the reference time, the gateway can act as an intermediary or "interpreter" between the time regimes of the fieldbuses. This function can optionally be implemented as a proxy functionality, in which the gateway provides a virtual image of a subscriber device of the first fieldbus and / or a virtual image of a subscriber device of the second fieldbus. The virtual images of the subscriber devices are configured to act as schedulers ("scheduler proxies") to negotiate or otherwise determine time slots for time-critical communication with subscriber devices of the other fieldbus. The negotiation or determination can be carried out, for example, in accordance with the standards defined by IEEE802.This can be done using the procedures defined in the 1QBv standard. Such a scheduler proxy can act as an interface for the protocols for setting up time slots for time-sensitive communication and can be addressed by the participant devices of a fieldbus in the same way as other participant devices of the same fieldbus. For example, a scheduler proxy can receive requests for time slots or issue corresponding confirmations according to a specified protocol. Since the gateway knows the first cycle time, the second cycle time, and the time offset from a reference time, the gateway can perform conversions of the time regimes. The gateway can output or receive converted times and / or time intervals in the respectively valid time regime via the scheduler proxy. This eliminates, for example, the need for conversion between the time regimes in the fieldbuses (e.g.at the application level), which simplifies the setup of time-sensitive communication.

[0020] In one embodiment, the method further comprises the step of communicating the first cycle time of the first time domain to the second fieldbus, and communicating the second cycle time of the second time domain to the first fieldbus via the gateway. Since the cycle time of the other fieldbus is known to the subscriber devices, this information can be used to plan communication. Optionally, the step also comprises communicating the time offset with respect to the reference time and the reference time itself to both fieldbuses via the gateway. This allows, if necessary, a conversion of the time regime to the other fieldbus.

[0021] In one embodiment, the method further comprises receiving, by the gateway, a request from the second subscriber device of the second fieldbus for a time slot for transmitting time-sensitive data from the first fieldbus to the second fieldbus, forwarding the request to the first subscriber device in the first fieldbus, receiving, by the gateway, a confirmation message from the first subscriber device of the first fieldbus, and forwarding the confirmation message from the gateway to the second subscriber device of the second fieldbus. For example, the first subscriber device in the first fieldbus is configured as a scheduler to receive such requests, reserve time slots accordingly, and generate and transmit confirmation messages. This can be achieved by the first subscriber device of the first fieldbus being able to execute the methods and protocols defined in the IEEE802.1QBv standard.In this way, a transfer of time-sensitive data between the fieldbuses can be set up.

[0022] In one embodiment, the method may further comprise the step of converting, by the gateway (30), times or intervals that relate to the time domain of one fieldbus into times or intervals that relate to the time domain of the respective other fieldbus. This allows the gateway to act as an "interpreter" between the time regimes of the first and second fieldbus. This can optionally even be configured such that the exchange of times and / or intervals takes place via proxy instances configured in the gateway, which represent a termination point of the corresponding communication protocols for each fieldbus. For example, a scheduler proxy for the first fieldbus can receive requests from the second fieldbus using the corresponding communication protocols of the second fieldbus.These requests can contain information about times and intervals according to the second time domain, with the gateway converting them to the time regime (time domain) of the first fieldbus and forwarding them to the first fieldbus. If an acknowledgment message or other response from the first fieldbus contains information about times or time intervals, these can be converted by the gateway into times and / or time intervals of the second fieldbus and output by the scheduler proxy to the corresponding participant device in the second fieldbus. In this way, participant devices can communicate with the other fieldbus without having to convert the exchanged times or intervals into the other time regime. This significantly simplifies the connection of fieldbuses with different time domains.

[0023] In an exemplary embodiment, the method further comprises the request by the second subscriber device of the second fieldbus for a time slot for transmitting time-sensitive data comprising an indication of one or more points in time and / or one or more time intervals related to the time domain of the second fieldbus. The gateway determines the one or more points in time or the one or more time intervals from the request related to the time domain of the first fieldbus, taking into account the time offset with respect to the reference point in time. The request forwarded to the first subscriber device in the first fieldbus then contains the indication of the one or more points in time or the one or more time intervals related to the time domain of the first fieldbus.The confirmation message from the first subscriber device of the first fieldbus may include an indication of one or more points in time and / or one or more time intervals that relate to the time domain of the second fieldbus. From this, the gateway determines the one or more points in time or the one or more time intervals from the confirmation message related to the time domain of the second fieldbus, taking into account the time offset with respect to the reference point in time, so that the confirmation message forwarded to the second subscriber device of the second fieldbus includes the indication of the one or more points in time or the one or more time intervals related to the time domain of the first fieldbus. Thus, there is no need to convert the time regimes in either the first fieldbus or the second fieldbus. Rather, the first orThe second fieldbus receives the time information from the other fieldbus relative to its own time regime. In an optional embodiment, the gateway can provide a scheduler proxy that acts as a protocol termination point for the second fieldbus and thus behaves like a participant device of the second fieldbus.

[0024] In one embodiment, the method can further comprise setting a first time slot for communicating time-sensitive data in the first fieldbus by the first subscriber device of the first fieldbus. The setting can be carried out in such a way that the first time slot of the first fieldbus and the second time slot of the second fieldbus overlap in time. In this case, the overlap area represents a temporal intersection, whereby time-sensitive data can be exchanged between the fieldbuses with no delay or only with small, manageable delays that satisfy a real-time requirement. This ensures that the instance (e.g., real-time supporting scheduler) that is set up locally for the first fieldbus is responsible for cross-fieldbus communication of time-sensitive real-time data.For example, a participant device with real-time scheduling function that already exists before the connection can be used for this purpose, so that only minimal changes to an existing fieldbus configuration are necessary.

[0025] In one embodiment, the method may further comprise the step of forwarding time-sensitive data from the second fieldbus to the first fieldbus or vice versa through the gateway during the overlap of the first time slot and the second time slot. This enables clocked end-to-end transmission between two subscriber devices across fieldbus boundaries. The forwarding can take place exclusively on the physical layer, for example, through an analog signal path through the gateway between connections for the first and second fieldbus. This allows delays in signal propagation times to be minimized. Acceptable forwarding of the time-sensitive data can also be achieved by the gateway providing a termination point for the physical layer on the second fieldbus side. The gateway can then receive the signals, demodulate them, and, if necessary, decode them (e.g.regarding channel coding), so that the time-sensitive data is available as data bits at the upper edge of the physical layer. These can then be passed on in the gateway to a physical interface on the first fieldbus, where coding (e.g. channel coding) and modulation for transmission to the first fieldbus may take place. For example, the data can be passed on in the so-called Medium Access (MAC) protocol layer via a so-called MAC bridge (e.g. according to the IEEE 802.1D standard). This allows, for example, the MAC protocol header to be read out and, if necessary, modified for forwarding to the other fieldbus. The data can also be passed on at a higher protocol layer than the MAC layer, with the gateway providing the corresponding protocol stack. Processing in the gateway can result in delays. Since the first orHowever, by reserving the second time slot for the transmission of time-sensitive data, intermediate storage in queues can be largely avoided. The resulting delays can thus be kept predictable and manageable, ensuring that real-time transmission requirements are met.

[0026] In one embodiment, the method can further comprise the transmission of non-time-sensitive data by the gateway, at times outside the first time slot of the first fieldbus and outside the second time slot of the second fieldbus, between the first fieldbus and the second fieldbus. This allows, for example, so-called best-effort data for configuring individual subscriber devices, or non-time-critical measurement data or command data to be exchanged between the fieldbuses, with the first and second time slots remaining reserved for the exchange of time-sensitive data between the fieldbuses. The gateway can temporarily store the data for best-effort data. An exchange of best-effort data is also possible if no common time slot is set up for the exchange of time-sensitive data between the fieldbuses.For example, the first and second fieldbuses can independently agree on time slots for transmitting time-sensitive data within the fieldbuses. The gateway can transmit the best-effort data at times outside of the time slots for transmitting time-sensitive data, possibly with intermediate storage. For example, the described requests and confirmation messages for agreeing on overlapping time slots for transmitting time-sensitive data can be transmitted between the fieldbuses in this way.

[0027] In practice, it is possible that, in addition to the time offset between the first and second time domains, further temporal differences exist, e.g., with regard to different durations of the first and second time slots and the temporal position of the first and second time slots for the transmission of time-sensitive data. In an area where the first and second time slots overlap, time-sensitive data can be passed between the fieldbuses through the gateway. Outside the overlap area, time slots can still be reserved in the first or second fieldbus for the transmission of time-sensitive data. These time periods can be used independently of one another, for example, for the transmission of time-sensitive data within the fieldbuses.

[0028] To implement the aforementioned frequency synchronization of the first and second time domains, the gateway can have a first timer and a second timer. To frequency synchronize the two fieldbuses, for example, the first timer can be synchronized as a slave with the first time domain of the first fieldbus. Furthermore, the second timer can be synchronized as a slave with the second time domain of the second fieldbus. Then, initially, only the frequency of the first timer can be synchronized as a slave with the frequency of the second time domain of the second timer, and then the first timer can be set as the master for the first fieldbus in order to set the frequency (of the first fieldbus) to the frequency of the first timer.

[0029] Since the gateway has its own timers that are synchronized (e.g., exclusively) in frequency, the gateway knows the time defined in the first and second time domains and can, for example, coordinate the transmission of non-time-sensitive data in such a way that the time slots for transmitting time-sensitive data are not affected. Furthermore, after frequency synchronization, it is guaranteed that the time differences between the fieldbuses, while still present, are time-invariant and thus do not "run away." In the described scenario, the first fieldbus derives its time base from the second fieldbus, whereby setting the first timer as the master for the first fieldbus represents only a minor intervention in the time regime of the first fieldbus. For example, setting the frequency of the first timer can be done over a period of time that avoids a hard time jump.The first fieldbus can thus be synchronized during operation "under load".

[0030] A further aspect of the invention relates to a system for networking at least two time-sensitive fieldbuses, comprising a first time-sensitive fieldbus, comprising a first subscriber device and a separate first time domain, wherein the first time domain contains first time slots for transmitting time-sensitive data. The system further comprises a second time-sensitive fieldbus, comprising a second subscriber device and a separate second time domain, wherein the second time domain contains second time slots for transmitting time-sensitive data. Furthermore, the system comprises at least one gateway that connects the first and second fieldbuses to one another for data transmission, wherein the gateway has means for determining a first cycle time of the first time domain and a second cycle time of the second time domain at a reference time.The gateway further comprises means for determining a time offset between the first time domain and the second time domain at the reference time. The system is configured, for example, to perform the steps (e.g., all steps) of the method described above.

[0031] A further aspect of the invention relates to a gateway for networking at least two time-sensitive fieldbuses with different time domains. The gateway has means for determining a first cycle time of a first time domain and a second cycle time of a second time domain at a reference time. Furthermore, the gateway has means for determining a time offset between the first time domain and the second time domain at the reference time. Embodiments of the gateway further comprise means for executing the (or any) method steps in the method described above, which are executed by the gateway mentioned therein.

[0032] Further embodiments of the invention emerge from the subclaims. Short description of the drawings

[0033] In the following detailed description, aspects of the invention are described with reference to the drawings, wherein Fig. 1 shows a block diagram of a system with a first time-sensitive fieldbus and with a second time-sensitive fieldbus; Fig. 2 schematically shows a timing diagram of a first and second fieldbus and the transmission of non-time-sensitive data through the gateway; Fig. 3 schematically shows a detailed timing diagram of the cycle times defined for a first and second fieldbus; and Fig. 4 schematically shows a timing diagram of a first and second fieldbus and the transmission of time-sensitive data through the gateway. Detailed description

[0034] The following detailed description explains exemplary embodiments of the invention with reference to the above-mentioned figures. In this case, identical reference symbols in different figures describe the same device, the same method step, the same time unit, etc.

[0035] Fig. 1shows a block diagram of an exemplary system 1 with a first time-sensitive fieldbus 10 and a second time-sensitive fieldbus 20. The first fieldbus 10 and the second fieldbus 20 comprise, by way of example, the participant devices 12, 14a-c, and 22, 24a-c, respectively, wherein the participant devices 12, 22 are each controllers of the fieldbus, for example an automation device, a programmable logic controller, PLC, a node or another industrial controller, and the participant devices 14a-c, and 24a-c are field devices, for example I / O modules for sensors and / or actuators, which can measure or influence variables of a process automated by the fieldbus. The subscriber devices 12, 14a-c, or 22, 24a-c are communicatively connected to each other in the respective fieldbus 10, 20 via an interface, whereby the definition of the interface includes an interface protocol.

[0036] The subscriber devices 12, 14a-c of the first fieldbus 10 belong to a first time domain 16, whereby all subscriber devices 12, 14a-c have the same understanding of absolute time. For this purpose, each subscriber device 12, 14a-c has a timer which is Fig. 1 schematically symbolized by the face of a clock. Correspondingly, the subscriber devices 22, 24a-c of the second fieldbus 20 belong to a second time domain 26. In the fieldbuses 10 and 20, the fieldbus lines are connected to the field devices in a star configuration, starting from the controller 12, 22. Generally, fieldbuses can also be formed by other topologies, e.g., tree topology, bus topology, or ring topology. It is also possible for the subscriber devices 12, 24a-c, or 22, 24a-c of a fieldbus 10, 20 to be at least partially interconnected by a wireless network.

[0037] Each participant device 12, 24a-c, or 22, 24a-c, sets the time for the respective fieldbus 10 or 20 and is therefore referred to as the master. For the first fieldbus 10, for example, the controller 12 is the master, which in Fig. 1 is shown as a clock face with solid lines. In the second fieldbus 20, for example, the subscriber device 24a is the fieldbus master. The clock of a master 12 or 24a specifies the time in the fieldbus, with the other subscriber devices of a fieldbus, i.e. subscriber devices 14a-c in the first fieldbus or subscriber devices 22, 24b-c, each deriving their time from the master. This occurs, for example, when the subscribers within a fieldbus exchange messages at regular or irregular intervals according to the Precision Time Protocol in accordance with the IEEE 1588 standard, and in this way establish and maintain a common understanding of time.

[0038] Within the first fieldbus 10 and the second fieldbus 20, both non-time-sensitive and time-sensitive data can be transmitted, as will be described in more detail below. For example, data transmission in both fieldbuses can be divided into transmission cycles according to the IEEE 802.1Q standards, with first time slots defined in the first fieldbus 10 and second time slots defined in the second fieldbus 20, in which real-time data can be transmitted between two subscriber devices of the same fieldbus. The transmission of real-time data can be a clocked end-to-end transmission between two subscriber devices, or a transmission with low delays that are known, deterministic, or causally controllable to the extent that they meet real-time requirements.

[0039] To define the transmission cycles and time slots for the transmission of time-sensitive data, one or more participant devices of the respective fieldbus can each have a scheduler function. The scheduler is responsible for defining the cycle times in the first or second fieldbus and communicating these to the other participant devices of the respective fieldbus. Furthermore, a scheduler can be configured to receive requests for the transmission of time-sensitive data in the first or second fieldbus, manage assigned time slots, communicate with a requesting participant device to negotiate time slots for time-sensitive transmission, and confirm or reject the requests accordingly. The scheduler can also be configured to communicate assigned time slots for the transmission of time-sensitive data to the other participant devices.In the following, it is assumed that in the first fieldbus 10, at least one of the subscriber devices 12, 24a-c can function as a scheduler and implements the corresponding protocols (e.g., according to the IEEE 802.1Q standard). Likewise, it is assumed that in the second fieldbus 20, at least one of the subscriber devices 22, 24a-c performs a scheduler function.

[0040] System 1 further comprises a gateway 30, via which both fieldbuses 10, 20 are communicatively connected to each other. Fig. 1that the fieldbuses 10, 20 are connected to each other via their controllers 12 and 22. However, this is not mandatory. Rather, the gateway 30 has an interface to each of the fieldbuses 10 and 20, so that it represents a subscriber device with respect to the respective fieldbus 10, 20. The gateway 30 supports at least two time domains 32 and 34. Additional time domains can be supported depending on the number of fieldbuses to be connected. In particular, the gateway includes timers 36 and 38, which can be configured for the first 16 and the second 26 time domains, respectively.

[0041] The gateway 30 further contains time conversion units 33 and 37. The time conversion units can be configured to act as "interpreters" between different time domains. For example, the time conversion unit 33 can be configured to receive time information (i.e., information regarding times and / or time intervals) that relate to the time domain 34 supported by the gateway 30 and to convert it into corresponding time information from the time domain 32. Conversely, the time conversion unit 33 can be configured to convert and output time information from the time domain 32 into that of the time domain 34. For the conversion, the time conversion unit 33 can, for example, determine a time offset between the timer 38 and 36 at a reference time and take it into account accordingly during the conversion.In a corresponding manner, the time conversion unit 37 can be configured to receive time information relating to the time domain 32 supported by the gateway and to convert it into corresponding time information of the time domain 34 or, in the opposite direction, to convert and output time information of the time domain 34 as time domain 32.

[0042] The gateway 30 can connect the first fieldbus 10 and the second fieldbus 20 for data transmission. For this purpose, the gateway 30 maintains a memory 35 for buffering or temporarily storing data. For example, non-time-sensitive data can be stored in the memory 35. However, the gateway 30 can also transmit time-sensitive data between the first and second fieldbuses 10, 20 during defined time slots. The time conversion units 33 and 37, respectively, can be used to define or negotiate such time slots. For example, the time conversion unit 33 can be configured to convert time information with respect to the first time domain 16 by communicating with subscriber devices of the second fieldbus 20, and in doing so, receive or output time information corresponding to the second time domain.In a corresponding manner, the time conversion unit 37 can communicate with subscriber devices of the first fieldbus 10 in order to receive or output time information relating to the first time domain 16 and to convert it relating to the second time domain 26.

[0043] Fig. 2 shows an exemplary time diagram of the first fieldbus 10 and the second fieldbus 20. Here, the first fieldbus 10 has communication or transmission cycles with periodically recurring cycle intervals TC1, which are determined in terms of position and duration according to the Fig. 2 The second fieldbus has 20 communication cycles with periodically recurring cycle intervals TC2, which are defined in terms of position and duration according to the Fig. 2 are defined in the lower timeline. In Fig. 2The inverse of the clock frequencies 1 / f1 and 1 / f2, namely the clock cycle duration, is represented by a black bar. Even if both clock frequencies f1 and f2 nominally (i.e., according to a specification) have the same frequencies, it is possible that the clocks of time domains 16 and 26 of the two fieldbuses run at different speeds if the actual values ​​of the clock frequencies f1 and f2 differ slightly.

[0044] In the fieldbuses 10, 20, first time slots 50 and second time slots 52 for transmitting time-sensitive data within the respective fieldbus 10, 20 can be defined, negotiated, or determined. For this purpose, for example, one of the subscriber devices 12, 14a-c in the first fieldbus 10 and one of the subscriber devices 22, 24a-c in the second fieldbus 20 can be configured as a real-time scheduler (time-aware scheduler) in accordance with the IEEE 802.1QBv standard. For example, the first time slots 50 and the second time slots 52 coincide with the beginning of the corresponding communication cycles. In general, the time slots 50, 52 for time-sensitive transmission can be located at any position within a transmission cycle. It is also possible to define several separate time slots 50, 52 for time-sensitive communication per transmission cycle.

[0045] Fig. 2Furthermore, time periods 54 and 56 are shown, which belong to the respective transmission cycles that lie outside the time slots 50 and 52 reserved for the transmission of time-sensitive data. In these intervals 54 and 56, non-time-sensitive data can be transmitted within the fieldbuses 10 and 20, for example, according to the Ethernet protocol, for which the CSMA / CD (Carrier Sense Multiple Access with Collision Detection) access method applies.

[0046] To connect the gateway 30, in one embodiment, the timers 36 and 38 of the gateway 30 are first synchronized as a slave with respect to the time domains 16, 26 of the fieldbuses 10 and 20. This provides the gateway with a synchronized interface as a subscriber device to both the first fieldbus 10 and the second fieldbus 20. Thus, the gateway 30 also knows the corresponding cycle times TC1 and TC2, the timing of the communication cycles, and the time slots 50 and 52 in which time-sensitive communication is processed in the respective fieldbuses 10, 20.

[0047] This makes it possible to initially exchange non-time-sensitive data between the fieldbuses. Such a transfer can be achieved, for example, by transmitting non-time-sensitive data 60 from the first fieldbus 10 to the gateway 30 during a first non-time-sensitive interval 54, as shown in Fig. 2symbolized by arrow 60. This data 60 can be buffered in the buffer memory 35 of the gateway 30, as symbolized by step 62. Finally, the buffered data can be transmitted from the gateway 30 to the second fieldbus 20 during intervals 56 outside the second time slots 52, as symbolized by arrow 64. For example, to transmit the data 64 to the second fieldbus using the CSMA / CD method or another contention method, the gateway 30 must ensure that the second fieldbus 20 is free for transmission during the time slots 56.

[0048] An exchange of non-time-sensitive data 60, 64 between the fieldbuses can be used to support frequency synchronization of the first time domain (16) and the second time domain (26). Through such synchronization of the timer clock frequencies, the time offset between the times of both time domains 16, 26 remains stable, thereby simplifying the determination of times in the gateway 30 or in the subscriber devices 12, 14a-c or 22, 24a-c of the first and second fieldbus with respect to the respective other time domain 16, 26. For this purpose, the following method for synchronizing the clock frequencies f1 and f2 of the timers 36 and 38 will be described as an example. In one embodiment, the clocks 36, 38 of the gateway 30 are initially synchronized as slaves of the first 16 or second 26 time domains and have the same nominal frequency.Frequency synchronization can now be achieved by designating the first timer 36 of the gateway 30 as the master for the first fieldbus 10, so that the gateway 30 can determine the timing in the first fieldbus. Furthermore, the frequency f1 of the first timer 36 of the gateway 30 can be synchronized to the frequency f2 of the second time domain 26. Synchronizing only the frequencies f1 and f2 in the time domains 16, 26 can prevent time jumps in the subscriber devices in the first fieldbus 10. The frequencies can be synchronized during ongoing operation of the first fieldbus 10 using an adjustment period that is selected long enough to allow the processes of the first fieldbus 10 to run smoothly.

[0049] Fig. 3schematically shows a detailed timing diagram of the cycle times defined for the first and second fieldbuses 10, 20 according to some aspects of the invention. In one example, the clock generators in the subscriber devices of the fieldbuses 10 and 20 may have the same clock frequencies f1 = f2, for example, according to the method described above. Fig. 3 is the inverse of the clock frequencies 1 / f1 or 1 / f2, namely the clock cycle duration, each illustrated by a black bar.

[0050] In the present example, only the clock frequencies between the first and second fieldbuses 10, 20 are synchronized. Therefore, a time offset 58 can occur between the start times of the communication cycles. Such a time offset 58 results, on the one hand, from the different definitions of time in the two fieldbuses 10, 20, and, on the other hand, from the difference between the start times of the communication cycles of the first fieldbus 10 and the second fieldbus 20, even if both fieldbuses had the same understanding of time. Furthermore, the communication cycles can have different durations TC1 and TC2. Therefore, the time offset 58 can generally only be defined with reference to an (absolute) reference time TRef. The absolute reference time TRef can be expressed accordingly both in the time of the first fieldbus 10 and in the time of the second fieldbus 20.If the time periods TC1 and TC2 are in a rational relationship to one another, a certain time offset 58 returns after a predictable number of cycles of the first or second fieldbus. For example, if the cycle time TC1 in the first fieldbus is 50 ms and the cycle time TC2 in the second fieldbus is 25 ms, the time offset 58 can be zero after a first cycle in the second fieldbus, 25 ms after a second cycle in the second fieldbus compared to the first fieldbus, and then zero again, and so on. However, if the time offset 58 is known at a time TRef, it is possible to determine the time offset 58 in advance for all communication cycles of the first and second fieldbus, even if the cycle time periods TC1 and TC2 are not in a rational relationship to one another.

[0051] Furthermore, different durations TS1 and TS2 of the first and second time slots 50 and 52 for time-sensitive communication can occur on fieldbuses 10 and 20, respectively, since these can be agreed upon independently for both fieldbuses 10 and 20. Furthermore, the first and second time slots 50 and 52 can exhibit temporal differences TD in their start times. These can generally only be predictably determined with reference to an absolute reference time TRef, since the start times of time slots 50 and 52 for time-sensitive communication can vary with the cycle times in the individual fieldbuses.

[0052] After frequency synchronization has been achieved, the gateway 30 can determine the cycle time durations TC1 and TC2 in the first and second fieldbuses 10, 20 at a reference time TRef. Furthermore, the gateway 30 can determine the time offset 58 between the first and second time domains 16, 26 at the reference time TRef. The gateway 30 can further communicate the cycle time duration TC1 of the first time domain 16 to the second fieldbus 20 and the cycle time duration TC2 of the second time domain 26 to the first fieldbus 10. This can be done with reference to the reference time TRef. In this way, specific subscriber devices of the first or second fieldbus 10, 20 can predictably determine the communication cycles of the other fieldbus 20, 10.

[0053] However, to establish overlapping first and second time slots in the first and second fieldbuses, respectively, for the communication of time-sensitive data, the gateway 30 can convert time information (i.e., times and / or intervals) such that no separate conversions need to be performed in the first fieldbus 10 and the second fieldbus 20. For this purpose, the gateway 30 is configured, as described above, by means of the time conversion units 33 and 37 to convert time information related to the first time domain 16 of the first fieldbus 10 into time information related to the second time domain 26 of the second fieldbus 20, taking into account the time offset 58 from the reference time TRef and vice versa.

[0054] In one embodiment, the time conversion unit 33 can optionally be further configured to function as a scheduler proxy for the second fieldbus 20, which can negotiate or determine time slots for time-critical communication with the first fieldbus. In this function, the time conversion unit 33 has an interface for establishing time slots in the first fieldbus for time-sensitive communication, for example, according to the methods defined by the IEEE802.1QBv standard. In this case, the subscriber devices 22, 24a-c of the second fieldbus 20 can address the time conversion unit 33 like a scheduler in their own fieldbus, i.e.send corresponding protocol messages for setting up time slots for the time-sensitive communication to the time conversion unit 33 and receive them from it, although a subscriber device configured as a scheduler (for example the controller 12) in the first fieldbus 10 is responsible for setting up time slots in the first fieldbus 10.

[0055] In one example, time-critical data is to be transmitted from the subscriber device 14c in the first fieldbus 10 to the subscriber device 24b in the second fieldbus 20. For this purpose, the subscriber device 24b knows the time conversion unit 33 configured as a scheduler proxy, to which it sends a request according to a negotiation protocol (e.g., as a scheduler according to IEEE802.1Q or another standard) containing time information (i.e., times and / or intervals) regarding possible time slots 52 with respect to the time domain 26 of the second fieldbus 20.

[0056] Upon receipt of the request, the time conversion unit 33 of the gateway 30 determines the corresponding time information for the time slots 52 with respect to the time domain 16 of the first fieldbus 10. This determination is made taking into account the time offset 58 with respect to the reference time TRef. The time conversion unit 33 forwards the request to the controller 12, which, for example, acts as a scheduler in the fieldbus 10. The forwarded request contains the time information related to the time domain 16 of the first fieldbus 10.

[0057] The controller 12 compares the proposed time information with the time slots it manages, for example, taking into account the cycle time TC1 applicable in the fieldbus 10, determines one or more time slots 52 for transmitting time-sensitive data, and sets them up through appropriate communication with the subscriber device 14c within the fieldbus 10. Furthermore, the controller 12 sends a confirmation message to the time conversion unit 33 of the gateway 30, which contains the time information for the time slot(s) 52. The latter time information applies with reference to the time domain 16 of the first fieldbus.

[0058] The time conversion unit 33 converts the time information into the time regime of the second fieldbus 20 and outputs it to the subscriber device 24b in the second fieldbus 20. The latter subscriber device can set the time slot(s) 52 with reference to its own time domain 26.

[0059] Thanks to the function of the time conversion unit 33, the subscriber devices in both time domains can determine their time information with reference to their own assigned time domain and do not require any internal conversion, e.g., at the application program level. The request protocol described is intended merely as an example. Other variants of a protocol for establishing time slots for time-sensitive communication are possible, whereby the communication of time information with the time conversion unit 33 can always be communicated with reference to the time domain of the respective fieldbus. Similarly, the time conversion unit 37 is available for requests or requests for time slots for transmitting time-sensitive data from the first fieldbus 10 to the second fieldbus 20.

[0060] Since the gateway 30 functions as a subscriber device with respect to the first fieldbus 10 and the second fieldbus 20, in some embodiments, the scheduler functionality for one or both fieldbuses 10 and 20 can also be assumed by the gateway 30. For example, the time conversion unit 33 can also assume a scheduler functionality for the first fieldbus 10 (instead of the controller 12). The gateway 30 can itself negotiate and configure time slots for the transmission of time-sensitive data in the first fieldbus 10, whereby the communication of time information in the first fieldbus 10 can take place with respect to the first time domain, and the communication of time information in the second fieldbus 20 can take place with respect to the second time domain.

[0061] Fig. 4shows a schematic timing diagram of a first fieldbus 10 and a second fieldbus 20 during a transmission of time-sensitive data. In the present case, for example, according to the protocol described above or a comparable protocol, time slots 50 were agreed in the first fieldbus 10 and time slots 52 were agreed in the second fieldbus 20 for the transmission of time-sensitive data from the subscriber device 14c to the subscriber device 24b, which at least partially overlap. In particular, corresponding subscriber devices of the first and second fieldbus have agreed on common overlap areas OL1 and OL2 in time slots 50 and 52, respectively, and have exchanged this information via the gateway 30 (for example, via the time conversion unit 33), so that this information is also known to the gateway 30.

[0062] In one embodiment, it is not necessary to create an overlap area OL1, OL2 for time-sensitive communication in each cycle TC1 or TC2 of the first or second fieldbus 10, 20. For example, it may be sufficient to define an overlap area during every second, third, etc. cycle of the first or second fieldbus 10, 20.

[0063] If the first and second time slots 50 and 52, respectively, reserved for time-sensitive communication within the fieldbuses are known during the communication cycles of the first and second fieldbuses 10, 20, the overlap areas OL1 and OL2 for time-sensitive communication between the fieldbuses can be determined or calculated based on rules. It is then sufficient to determine a single pair of overlapping time slots 50 and 52 at a reference time TRef. The reservation of the time slots 50 and 52 can be performed by subscriber devices acting as schedulers in the first and second fieldbuses, respectively. In one embodiment, the time conversion units 33 and 37 of the gateway 30 can provide the time information for the first and second time slots 50 and 52, respectively, with respect to the fieldbus's own time domain. The determination of the overlap areas OL1 and OL2 can thus also be carried out with respect to the fieldbus' own time domain.

[0064] If the cycle times TC1 and TC2 are in a rational relationship to each other, regularly recurring overlap areas OL1 and OL2 result. In this case, the negotiation and / or determination of time slots 50 and 52 is simplified, so that in these cases an overlap area OL1, OL2 recurs regularly and therefore does not need to be negotiated or determined individually.

[0065] In one embodiment, the gateway 30 is further configured to transmit time-critical data 70, 72 during the temporally overlapping time slots, e.g., OL1 and OL2, respectively. In one embodiment, this is achieved by the gateway 30 determining the time slots for time-sensitive transmission 50 and 52 determined between the first and second fieldbuses 10, 20, and in particular the respective overlap intervals OL1, OL2, and passing the signals between the first and second fieldbuses during these intervals.

[0066] Using the described method, System 1, and Gateway 30, it is possible to network time-sensitive fieldbuses 10, 20 without having to align the fieldbus times and communication cycles of the fieldbuses. This allows existing and sometimes incompatible fieldbuses to be configured for the exchange of both non-time-sensitive and time-sensitive data.

Claims

1. Method for interconnecting a first time-sensitive field bus (10) with a second time-sensitive field bus (20), wherein the first time-sensitive field bus (10) comprises a first subscriber device (12, 14) and has its own first time domain (16), and wherein the second time-sensitive field bus (20) comprises a second subscriber device (22, 24) and has its own second time domain (26), wherein the first time domain (16) and the second time domain (26) being frequency-synchronized, wherein the first and second field buses (10, 20) being interconnected to each other by means of a gateway (30) for data transmission, the method comprising the following steps: - determining a first cycle time duration (TC1) of the first time domain (16) and a second cycle time duration (TC2) of the second time domain (26) by the gateway (30) at a reference time point (TRef); and - determining a time offset (58) between the first time domain (16) and the second time domain (26) by the gateway (30) at the reference time point (TRef).

2. Method according to claim 1, further comprising the step of communicating the first cycle time duration (TC1) of the first time domain (16) to the second field bus (20) and communicating the second cycle time duration (TC2) of the second time domain (26) to the first field bus (10) by the gateway (30).

3. Method according to claim 1 or 2, wherein the method further comprises the steps of: - receiving by the gateway (30) a request from the second subscriber device (22, 24) of the second field bus (20) of a time slot (50) for transmitting time-sensitive data from the first field bus (10) to the second field bus (20); - forwarding by the gateway (30) of the request to the first subscriber device (12, 14) in the first field bus (10); - receiving by the gateway (30) a confirmation message from the first subscriber device (12, 14) of the first field bus (10); and - forwarding the confirmation message from the gateway (30) to the second subscriber device (22, 24) of the second field bus (20).

4. Method according to one of claims 1 to 3, wherein the method further comprises the step of converting, by the gateway (30), time points or intervals relating to the time domain of one fieldbus into time points or intervals relating to the time domain of the respective other fieldbus.

5. Method according to one of claims 3 or 4, wherein: - the request of the second subscriber device (22, 24) of the second field bus (20) of a time slot (50) for transmitting time-sensitive data comprises an indication of one or more time points and / or one or more time intervals relating to the time domain (26) of the second field bus (20); - the method further comprises determining, by the gateway (30), the one or more points in time and / or the one or more time intervals from the request related to the time domain (16) of the first field bus (10), taking into account the time offset (58) with respect to the reference time point (TRef); - wherein the forwarded request to the first subscriber device (12, 14) in the first field bus (10) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10); - wherein the confirmation message from the first subscriber device (12, 14) of the first field bus (10) comprises an indication of one or more points in time and / or one or more time intervals related to the time domain (16) of the second field bus (10); - the method further comprising determining, by the gateway (30), the one or more time points and / or the one or more time intervals from the confirmation message with respect to the time domain (26) of the second field bus (20), taking into account the time offset (58) with respect to the reference time point (TRef); and - wherein the forwarded confirmation message to the second subscriber device (22, 24) of the second field bus (20) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10).

6. Method according to any one of claims 1 to 5, wherein the method further comprises the steps of: - setting a first time slot (50) for communicating time-sensitive data in the first field bus (10) by the first subscriber device (12, 14) of the first field bus (10); and - setting a second time slot (52) for the communication of time-sensitive data in the second field bus (20) by the second subscriber device (22, 24) of the second field bus; - wherein the setting being carried out in each case in such a way that the first time slot (50) of the first field bus (10) and the second time slot (52) of the second field bus (20) overlap in time (OL1, OL2).

7. Method according to claim 6, wherein the method further comprises the following step: passing time-sensitive data from the second field bus (20) to the first field bus (10) or vice versa by the gateway (30) during the overlap (OL1, OL2) of the first time slot (50) and the second time slot (52).

8. Method according to claim 6, wherein the method further comprises the steps of: transmitting non-time sensitive data, by the gateway (30), in times outside the first time slot (50) of the first field bus (10) and outside the second time slot (52) of the second field bus (20) between the first field bus (10) and the second field bus (20).

9. Method according to any one of claims 1 to 6, wherein between the first time domain (16) and the second time domain (26) is given: - different durations (TS1, TS2) of the first and second time slots (50, 52); and / or - temporal differences (TD) between first and second time slots (50, 52).

10. Method according to any one of claims 1 to 9, wherein the gateway (30) comprises a first timer (36) and a second timer (38), and the method for frequency synchronization of the two field buses (10, 20) further comprises the following steps: - synchronizing the first timer (36) as a slave with the first time domain (16) of the first field bus (10); - synchronizing the second timer (38) as a slave with the second time domain (26) of the second field bus (20); - initially synchronizing only the frequency of the first timer (36) as a slave with the frequency (f2) of the second time domain (26) of the second timer (38); and then - setting the first timer (36) as master for the first field bus (10) in order to set the frequency (f1) of the first field bus (10) to the frequency of the first timer (38).

11. Gateway (30) for interconnecting at least two time-sensitive field buses (10, 20) with different time domains (16, 26), wherein the different time domains are frequency-synchronized, comprising: - means for determining a first cycle time duration (TC1) of the first time domain (10) and a second cycle time duration (TC2) of the second time domain (20) at a reference time point (TRef); and - means for determining a time offset (58) between the first time domain (16) and the second time domain (26) at the reference time point (TRef).

12. Gateway according to claim 11, further comprising: - Means for communicating the first cycle time duration (TC1) of the first time domain (16) to the second field bus (20) and for communicating the second cycle time duration (TC2) of the second time domain (26) to the first field bus (10).

13. Gateway according to one of claims 11 or 12, further comprising - means for receiving a request from the second subscriber device (22, 24) of the field bus (20) of a time slot (50), for transmitting time-sensitive data from the first field bus (10) to the second field bus (20); - means for forwarding the request to a first subscriber device (12, 14) in the first field bus (10); - means for receiving an acknowledgement message from the first subscriber device (12, 14) of the first field bus (10); and - means for forwarding the confirmation message from the gateway (30) to the second subscriber device (22, 24) of the second field bus (20).

14. Gateway (30) according to one of claims 11 to 13, wherein the gateway (30) is further arranged for converting time points or intervals relating to the time domain of one fieldbus into time points or intervals relating to the time domain of the respective other fieldbus.

15. Gateway according to one of claims 13 or 14, wherein: - the request of the second field bus (20) for a time slot (50) for transmitting time-sensitive data comprises an indication of one or more time points and / or one or more time intervals, which are related to the time domain (26) of the second field bus (20); - the gateway (30) further comprises means for determining the one or more points in time and / or the one or more time intervals from the request related to the time domain (16) of the first field bus (10), taking into account the time offset (58) with respect to the reference time point (TRef); - wherein the forwarded request to the first subscriber device (12, 14) in the first field bus (10) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10); - wherein the confirmation message from the first subscriber device (12, 14) of the first field bus (10) comprises an indication of one or more time points and / or one or more time intervals related to the time domain (16) of the second field bus (10); - the gateway (30) further comprises means for determining the one or more points in time and / or the one or more time intervals from the confirmation message with respect to the time domain (26) of the second field bus (20), taking into account the time offset (58) with respect to the reference time point (TRef); and - wherein the forwarded confirmation message to the second field bus (20) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10).

16. Gateway according to one of claims 13 to 15, wherein the gateway (30) comprises means for passing time-sensitive data from the second fieldbus (20) to the first fieldbus (10) or vice versa during an overlap (OL1, OL2) of a first time slot (50) of the first fieldbus (10) and a second time slot (52) of the second fieldbus (20).

17. System (1) for interconnecting at least two time-sensitive field buses (10, 20), comprising: - a first time-sensitive field bus (10), comprising a first subscriber device (12, 14) and a separate first time domain (16), wherein the first time domain (16) comprising first time slots (50) for transmitting time-sensitive data; - a second time-sensitive field bus (20), comprising a second subscriber device (22, 24) and a separate second time domain (26), wherein the second time domain (26) comprising second time slots (52) for transmitting time-sensitive data; and - at least one gateway (30), according to one of claims 11 to 16, which interconnects the first and second field buses (10, 20) for data transmission.

18. System according to claim 17, - wherein the gateway (30) comprises means for communicating the first cycle time duration (TC1) of the first time domain (16) to the second field bus (20) and communicating the second cycle time duration (TC2) of the second time domain (26) to the first field bus (10).

19. System according to one of claims 17 or 18, wherein - the gateway (30) comprises means for receiving a request from a second subscriber device (22, 24) of the second field bus (20) of a time slot for transmitting time-sensitive data from the first field bus (10) to the second field bus (20); - the gateway (30) comprises means for forwarding the request to the first subscriber device (12, 14) in the first field bus (10); - the gateway (30) comprises means for receiving an acknowledgement message from the first subscriber device (13, 14) of the first field bus (10); and - the gateway (30) comprises means for forwarding the confirmation message from the gateway (30) to the second subscriber device (22, 24) of the second field bus (20).

20. System according to one of claims 17 to 19, wherein the gateway (30) is further arranged for converting time points or intervals relating to the time domain of one fieldbus into time points or intervals relating to the time domain of the respective other fieldbus.

21. System according to one of claims 19 or 20, wherein: - the request from the second subscriber device (22, 24) of the second field bus (20) for a time slot (50) for transmitting time-sensitive data comprises an indication of one or more time points and / or one or more time intervals related to the time domain (26) of the second field bus (20); - the gateway (30) further comprises means for determining the one or more points in time and / or the one or more time intervals from the request related to the time domain (16) of the first field bus (10), taking into account the time offset (58) with respect to the reference time point (TRef); - wherein the forwarded request to the first subscriber device (12, 14) in the first field bus (10) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10); - wherein the confirmation message from the first subscriber device (12, 14) of the first field bus (10) comprises an indication of one or more time points and / or one or more time intervals related to the time domain (16) of the second field bus (10); - the gateway (30) further comprises means for determining the one or more points in time and / or the one or more time intervals from the confirmation message with respect to the time domain (26) of the second field bus (20), taking into account the time offset (58) with respect to the reference time point (TRef); and - wherein the forwarded confirmation message to the second field bus (20) comprises the indication of the one or more time points or the one or more time intervals with respect to the time domain (16) of the first field bus (10) .

22. System according to one of claims 17 to 21, wherein - the first subscriber device (12, 14) of the first field bus (10) is set up to set a first time slot (50) in the first field bus (10), for communicating time-sensitive data; - the second subscriber device (22, 24) of the second field bus (20) is set up for setting a second time slot (52) in the second field bus (20), for communicating time-sensitive data; and - the setting is carried out in each case in such a way that the first time slot (50) of the first field bus (10) and the second time slot (52) of the second field bus (20) overlap in time (OL1, OL2).

23. System according to claim 22, wherein the gateway (30) comprises means for passing time-sensitive data, during the overlapping (OL1, OL2) of the first time slot (50) and the second time slot (52), from the second field bus (20) to the first field bus (10) or vice versa.