DE10234145A1 - Method for arbitrating access to a data bus - Google Patents

Abstract

The invention relates to a method for arbitrating access to a data bus between subscribers (Tn1, Tn2 ...), the subscribers being coupled by at least one arbitration ring (12; 38, 40, 42, 44, 46, 48) with the following Steps: DOLLAR A a) request for access by a first of the participants, DOLLAR A b) check whether a first signal to indicate that the arbitration ring is available is present at an input (16) of the first participant, DOLLAR A c) output ( 18) a second signal by the first participant when the first signal is present, DOLLAR A d) checking whether the first signal is still present at the input of the first participant at the end of a predetermined time interval, DOLLAR A e) access by the first participant if the first signal was still present at the end of the specified time interval.

Description

The invention relates to a method for arbitration Access to a data bus, the participants through at least one arbitration ring are coupled, and one corresponding participants and a communication system.

Under a synchronous, clocked communication system with A system understands equidistance properties at least two participants who are on a data network for the purpose of mutual exchange of data or the mutual Transmission of data are interconnected. there The data exchange takes place cyclically in equidistant Communication cycles by the used by the system Communication clock can be specified. Participants are, for example central automation devices, programming, Configuration or operating devices, peripheral devices such as B. Input / output modules, drives, actuators, sensors, programmable logic controllers (PLC) or other control units, Computers, or machines that share electronic data with others Exchange machines, especially data from others Process machines. Participants also become network nodes or Called knot. Below are control units Regulator or control units of any kind understood but also, for example, switches and / or switch controllers. As data networks, for example, bus systems such. B. Fieldbus, Profibus, Ethernet, Industrial Ethernet, FireWire or also PC internal bus systems (PCI), etc., in particular but isochronous realtime ethernet is also used.

Data networks enable communication between several Participants through networking, i.e. connecting the individual participants among themselves. Communication means that Transfer of data between participants. The too transmitted data are sent as data telegrams, d. H. the data is packed into several packages and in this form via the data network to the corresponding Recipient sent. One therefore speaks of data packets. The term transmission of data is used in this Document completely synonymous with the transfer of Data telegrams or data packets used.

In distributed automation systems, for example in Drive technology area, certain data must be certain Times arrive at the designated participants and processed by the recipients. One speaks of real-time critical data or data traffic, as a not timely arrival of the data at the destination leads to undesirable results for the participant, in contrast to not real-time critical, for example inter- or intranet-based data communication. According to IEC 61491, EN61491 SERCOS interface - Brief technical description (http: / / www.sercos.de/deutsch/index_deutsch.htm) can successful real-time critical data traffic of the type mentioned can be guaranteed in distributed automation systems.

Automation components (e.g. controls, drives,...) generally have an interface to today a cyclically clocked communication system. A Execution level of the automation component (fast cycle) (e.g. Position control in a controller, torque control of a drive) is synchronized to the communication cycle. This will the communication clock is fixed. Other, low-performing Algorithms (slow cycle) (e.g. temperature controls) of the Automation components can also only use this Communication clock with other components (e.g. Binary switch for fans, pumps,. , .) communicate, although a slower cycle would be sufficient. By using only one Communication clock for the transmission of all information the system places high demands on the bandwidth of the Transmission link.

Various are centralized from the prior art and decentralized arbitration procedures for access to known a data bus. With the centralized A central arbiter decides which arbitration procedure Bus subscriber who has made an access request, access gets on the bus. An example of a centralized Arbitration is the round robin algorithm.

In the case of decentralized arbitration procedures, the Bus arbitration decentralized in every bus participant. An example for one such method is the daisy chain algorithm.

The invention has for its object an improved To create arbitration procedures as well as an improved one Participants and a communication system.

The objects underlying the invention are with the Features of the corresponding independent claims solved in each case. Preferred embodiments of the invention are specified in the dependent claims.

The invention enables the creation of a Communication system in which the number of arbitration rings is independent on the number of bus participants. The corresponding Arbitration procedure works independently of that Number of participants and is therefore in principle arbitrary scalable. A maximum delay time for the Access to a bus, the so-called latency time, be guaranteed.

According to a preferred embodiment of the invention Access requests of different priorities supported by one for each of the possible priorities separate arbitration ring is provided.

• - ist jedem Busteilnehmer eine Arbitrierungseinheit zugeordnet,
• - kann jede Arbitrierungseinheit eines Busteilnehmers z. B. zwei Prioritäten LP und HP unterstützen, wobei LP die niedrige Priorität und HP die hohe Priorität kennzeichnet.

According to a further preferred embodiment of the invention

• an arbitration unit is assigned to each bus subscriber,
• - Each arbitration unit of a bus participant z. B. support two priorities LP and HP, with LP identifying the low priority and HP identifying the high priority.

According to a further preferred embodiment of the invention are the arbitration units of the bus participants for two supported priorities to a lower priority ring and interconnected in a high priority ring. It is advantageous when the arbitration unit of a bus participant lower priority ring can interrupt so none combinatorial feedback occurs. This bus participant is the low priority ringmaster.

• - ist der niederpriore Ringmaster immer der aktuelle Busmaster, der Schreib- und Lesezugriffe über den Bus ausführen kann,
• - kann jeder Busteilnehmer der niederpriore Ringmaster und damit Busmaster werden,
• - wird ein Busteilnehmer der neue niederpriore Ringmaster,
• - wenn bei diesem Busteilnehmer der niederpriore Bus- Request aktiviert ist und
• - der bisherige Busmaster bereit ist, sein Buszugriffsrecht abzugeben und
• - kein weiterer niederpriorer Busrequest eines Busteilnehmers zwischen dem alten und dem neuen niederprioren Ringmaster anliegt,
• - muss immer die Arbitrierungseinheit eines Busteilnehmers den hochprioren Ring unterbrechen, damit keine kombinatorische Rückkopplung auftritt. Dieser Busteilnehmer ist der hochpriore Ringmaster,
• - kann jeder Busteilnehmer der hochpriore Ringmaster werden,
• - muss ein Busteilnehmer der als Busmaster hochpriore Schreib- und Lesezugriffe ausführt, sowohl niederpriorer Ringmaster als auch hochpriorer Ringmaster sein,
• - muss ein Busteilnehmer der als Busmaster niederpriore Schreib- und Lesezugriffe ausführt, der niederpriore Ringmaster sein,
• - ist ein hochpriorer Ringmaster zum Masterwechsel am hochprioren Ring bereit, wenn
• - kein hochpriorer Busrequest bei diesem Busteilnehmer anliegt oder
• - ein hochpriorer Busrequest anliegt und dieser Busteilnehmer bereits Busmaster ist.

According to a further preferred embodiment of the invention

• - the lower priority ring master is always the current bus master, which can carry out write and read accesses via the bus,
• - every bus participant can become the lower priority ring master and thus bus master,
• - If a bus participant becomes the new low-priority ring master,
• - if the low-priority bus request is activated for this bus device and
• - the previous bus master is ready to give up his bus access right and
• - there is no further low-priority bus request from a bus subscriber between the old and the new low-priority ring master,
• - The arbitration unit of a bus subscriber must always interrupt the high-priority ring so that no combinatorial feedback occurs. This bus participant is the high priority ring master,
• - every bus participant can become the high-priority ring master,
• - a bus participant who carries out high priority write and read accesses as bus master must be both low priority ring master and high priority ring master,
• - A bus participant who carries out write and read accesses as bus master with low priority must be the lower priority ring master,
• - a high priority ring master is ready to change the master on the high priority ring if
• - there is no high priority bus request from this bus subscriber or
• - A high priority bus request is pending and this bus participant is already the bus master.

Is one of the above both conditions is met on Output of the arbitration unit of the high priority ring master the signal level for "HP ring released" on the high priority ring output.

The high priority ring master receives the signal level "HP ring released "at the exit of his arbitration unit placed on the high priority ring, again at the entrance of his Arbitration unit, no other bus participant has one high priority bus request. In this case it happens no change of master on the high priority ring.

Neither condition is met if the high priority Ringmaster despite an activated high priority bus request is not the bus master. In this case the Arbitration unit of the high priority ring master Signal level for "HP ring occupied" output on the high-priority ring.

• - wird ein Busteilnehmer ab dem nächsten Bustakt der neue hochpriore Ringmaster, wenn folgende Bedingungen erfüllt sind,
• - der hochpriore Bus-Request muss aktiviert sein,
• - am Eingang seiner Arbitrierungseinheit muss der Signalpegel für "HP-Ring freigegeben" anliegen.

According to a further preferred embodiment of the invention

• - a bus participant becomes the new high-priority ring master from the next bus cycle if the following conditions are met,
• - the high priority bus request must be activated,
• - The signal level for "HP ring released" must be present at the input of its arbitration unit.

So that these conditions do not apply to the current bus cycle other bus participants are met and there is only one high priority ring master, this bus participant gives on Output of its arbitration unit the signal level for "HP- Ring occupied "on the high priority ring. This signal level remains activated until the new high-priority ring master is ready to change the master on the high priority ring and on the Signal level for "HP ring released" on the high priority ring switches.

Is a bus device after initialization of the bus system preset as bus master and as high priority ring master, can the maximum access time in each arbitration unit be parameterized on the bus.

The default is a bus cycle. A bus master can do that Right of access to the bus at any time before the maximum access time has expired hand in again. If another bus participant has a (low or high-priority) bus request, the Arbitration unit of the current bus master the bus access right at the latest after the maximum access time has expired. If the maximum access time has expired, this takes place Master change even if this is the case with the previous bus master Bus request is still set. As long as no other Bus participant makes a (low or high priority) bus request, the current bus master also retains the bus access right Expiration of the maximum access time.

According to a further preferred embodiment of the invention there can be a pause in each arbitration unit be parameterized, which must run before a bus master after Submission of his bus access right can become bus master again. The default is a bus cycle. This pause time will also then complied with if the bus subscriber has a lower priority or high priority bus request to its arbitration unit has asked.

• - Solange der aktuelle Busmaster das Buszugriffsrecht behalten will, aktiviert die Arbitrierungseinheit des Busmasters "Bus belegt" (z. B. eine logische 0) am niederprioren Ring.
• - Ist der aktuelle Busmaster bereit das Buszugriffsrecht abzugeben, aktiviert dessen Arbitrierungseinheit "Busfreigabe" (z. B. eine logische 1) am niederprioren Ring.
• - Damit ein Busteilnehmer, der einen niederprioren Bus- Request an seine Arbitrierungseinheit gestellt hat, der neue Busmaster werden kann, müssen folgende Bedingungen erfüllt sein:
• - am hochprioren Eingang seiner Arbitrierungseinheit muss der Signalpegel für "HP-Ring freigegeben" anliegen,
• - am niederprioren Eingang seiner Arbitrierungseinheit muss der Signalpegel für "Busfreigabe" anliegen,
• - die parametrierte Pausezeit zwischen Abgabe und erneutem Erhalt des Buszugriffsrechts muss abgelaufen sein.

According to a further preferred embodiment of the invention, the following sequence of arbitration results with two supported priorities:

• - As long as the current bus master wants to keep the bus access right, the arbitration unit of the bus master activates "Bus occupied" (e.g. a logical 0) on the lower priority ring.
• - If the current bus master is ready to hand over the bus access right, its arbitration unit activates "bus release" (eg a logical 1) on the lower priority ring.
• - The following conditions must be fulfilled so that a bus node that has made a low-priority bus request to its arbitration unit can become the new bus master:
• the signal level for "HP ring released" must be present at the high-priority input of its arbitration unit,
• the signal level for "bus release" must be present at the low-priority input of its arbitration unit,
• - The parameterized pause time between delivery and renewed receipt of the bus access right must have expired.

If all conditions are met, this bus participant is off the next bus cycle the new bus master. So in the current Bus clock these conditions do not apply to others Bus participants are met and there can only be one bus master, gives this bus participant at the exit of his Arbitration unit the signal level for "Bus occupied" on the lower priority ring out. This signal level remains activated until the new one Busmaster is ready to surrender the bus access right again and the signal level for "bus release" on the lower priority Ring switches.

If a bus master receives the signal level "bus release" it at the output of its arbitration unit on the lower priorities Ring has put back at the entrance of his Arbitration unit, are in the current bus clock of no bus participant Conditions for a master change on the bus have been met. In In this case the current bus master keeps this Bus access right and can further write or read access to the run shared resources until another Bus participant makes a bus request.

• - der Busteilnehmer muss der hochpriore Ringmaster sein,
• - am niederprioren Eingang seiner Arbitrierungseinheit muss der Signalpegel für "Busfreigabe" anliegen,
• - die parametrierte Pausezeit zwischen Abgabe und erneutem Erhalt des Buszugriffsrechts muss abgelaufen sein.

The following conditions must be fulfilled so that a bus node that has made a high-priority bus request to its arbitration unit can become the new bus master:

• - the bus participant must be the high-priority ring master,
• the signal level for "bus release" must be present at the low-priority input of its arbitration unit,
• - The parameterized pause time between delivery and renewed receipt of the bus access right must have expired.

If all conditions are met, this bus participant is off the next bus cycle the new bus master. Since the Arbitration units of the bus participants form a ring with this method an equal treatment of the bus participants and one Maximum delay time from bus request to bus assignment ensured.

If further priorities are required, there is an additional one for each Priority another priority ring required.

• - an jedem der höherprioren Eingänge seiner Arbitrierungseinheit muss jeweils der Signalpegel für "Ring freigegeben" anliegen,
• - der Busteilnehmer muss der Ringmaster dieser Prioritätsebene N sein,
• - am niederprioren Eingang seiner Arbitrierungseinheit muss der Signalpegel für "Busfreigabe" anliegen,
• - die parametrierte Pausezeit zwischen Abgabe und erneutem Erhalt des Buszugriffsrechts muss abgelaufen sein.

Otherwise, the above statements still apply, with the following generalization:
The following conditions must be fulfilled so that a bus participant who has made a bus request of a given priority N to its arbitration unit can become the new bus master:

• the signal level for "ring released" must be present at each of the higher priority inputs of its arbitration unit,
• the bus subscriber must be the ring master of this priority level N,
• the signal level for "bus release" must be present at the low-priority input of its arbitration unit,
• - The parameterized pause time between delivery and renewed receipt of the bus access right must have expired.

If all conditions are met, this bus participant the new bus master from the next bus cycle.

This procedure meets all the requirements for a powerful arbitration process, at the same time minimal planning and project planning.

The use of the arbitration procedure described is especially with real-time Ethernet communication in the fieldbus Range possible.

It is also of particular advantage that the disclosed methods in automation systems, in particular in and in packaging machines, presses, Plastic injection machines, textile machines, printing machines, machine tools, Robots, handling systems, woodworking machines, Glass processing machines, ceramic processing machines as well Hoists can be used or used.

Preferred exemplary embodiments of the Invention explained with reference to the drawings. It demonstrate:

Fig. 1 arbitration with priority - state after reset, subscriber 2 is the bus master,

Fig. 2 is a flow diagram of an embodiment of a method according to the invention with a priority,

Fig. 3 arbitration with priority - activate subscriber 1 and 4 Busrequest, subscriber 4 is a bus master, with timing diagram

Fig. 4 arbitration with priority - subscriber 4 disabled bus request; Participant 1 becomes bus master, with timing diagram,

Fig. 5 arbitration with priority - subscriber 1 remains disabled bus request and bus master, with timing diagram

Fig. 6 arbitration with three priorities - state after reset; Participant 2 is bus master,

Fig. 7 shows an embodiment of a method according to the invention having a plurality of priorities,

Fig. 8 arbitration with three priorities - User 3, 4 and 5 enable bus requests of different priority; Participant 5 becomes bus master,

Fig. 9 arbitration with three priorities - Participants 5 disabled bus request; Participant 4 becomes bus master,

Fig. 10 arbitration with three priorities - Participants 4 disabled bus request; Participant 3 becomes bus master,

Fig. 11 arbitration with three priorities - subscriber 4 and 6 enable bus requests of different priority; Participant 3 deactivates bus request; Participant 6 becomes bus master,

Fig. 12 arbitration with three priorities and virtual participants - state after reset; Participant 2 is bus master,

Fig. 13 shows an embodiment of a method according to the invention with an arbitration unit as a virtual subscriber,

Fig. 14 arbitration with three priorities and virtual participants - activate subscriber 1, 3 and 4 bus requests of different priority; Participant 3 becomes bus master,

Fig. 15 arbitration with three priorities and virtual participants - Participant 2 activates bus request; Participant 3 deactivates bus request; Participant 4 becomes bus master,

Fig. 16 arbitration with three priorities and virtual participants - Participant 3 activates bus request; Participant 4 deactivated bus request; Participant 1 becomes bus master,

FIG. 17 arbitration with three priorities and virtual participants - participants 1 deactivated Busrequest; Participant 3 becomes bus master,

Fig. 18 Arbitration with three priorities and virtual participants - participant 3 deactivates bus request: participant 2 becomes bus master,

Fig. 19 Arbitration with three priorities and virtual nodes - node 2 deactivates bus request and remains bus master.

Fig. 1 shows a block diagram of a communication system according to the invention. The communication system includes a data bus 10 which the subscribers Tn 1, Tn 2, Tn 3, Tn 4 and Tn 5 of the communication system can access. The participants Tn 1 to Tn 5 are coupled by an arbitration ring 12 . The arbitration ring 12 has a circumferential direction, which, in the exemplary embodiment considered here, is clockwise.

Figs. 1 shows the state after reset: The participant Tn 2 is bus master and master ring, as long as no access request that is, a so-called bus request is activated. A bus request can, for example, be generated by an application of a subscriber. In the following, “bus master” is understood to mean the subscriber who is allowed to access the data bus 10 .

Each of the participants Tn 1 to Tn 5 has an arbitration module 14 with an input 16 and an output 18 . The signal "Bus / ring occupied" or "Bus / ring enabled" can be received at input 16 . The signal at input 16 is generally output unchanged at output 18 .

Only if a participant has the role of a ring master for the arbitration ring 12 can this participant, in the case of the "bus / ring occupied" signal at its input 16 , output the "bus / ring released" signal at its output 18 . In the configuration considered here, the bus master and the ring master are identical since there is only one arbitration ring 12 . In the example considered here, the bus master and the ring master are the subscribers Tn 2.

The flow diagram of FIG. 2 illustrates the mode of operation of the communication system of FIG. 1. In step 20 , one of the subscribers Tn X is the bus master and at the same time the ring master. The subscriber Tn X has current access to the data bus 10 , so that the "bus / ring occupied" signal circulates on the arbitration ring 12 .

In step 22 , the subscriber Tn X wants to release the data bus 10 . The reason for this may be that the subscriber Tn X no longer has a bus request or that a predetermined maximum time for occupying the data bus has expired. Since the subscriber Tn X is the ring master, he can output the "bus / ring released" signal at his output 18 , which is done in step 22 .

In step 24 , another of the participants Tn Y has an access request. This can come from an application of the subscriber Tn Y. In step 26, the subscriber Tn Y checks whether the signal "bus / ring released" is present at its input 16 . If this is not the case, the subscriber Tn Y must wait until this signal is present at its input 16 .

As soon as the "bus / ring released" signal is present at the input 16 of the subscriber Tn Y, the subscriber Tn Y outputs the signal "bus / ring occupied" at its output 18 in step 28 . This takes place, for example, at the beginning of a bus cycle.

In step 30, the subscriber Tn Y checks whether the "bus / ring enabled" signal is still present at its input 16 at the end of the bus cycle. If this is the case, it means that either no other of the subscribers has issued a "bus / ring occupied" signal to the arbitration ring 12 after the "bus / ring released" signal was present, or that another subscriber did such a signal "Bus / ring occupied", but this subscriber is further away from the current ring master in the sense of rotation of the arbitration ring 12 than the subscriber Tn Y. Advantageously, the length of the bus clock is essentially equal to the length for the circulation of a signal around the arbitration ring 12 or chosen longer.

If the condition of step 30 is fulfilled, the subscriber Tn Y in step 32 becomes a new bus master and at the same time a new ring master for the arbitration ring 12 . If the condition of step 30 is not met, the sequence control of the subscriber Tn Y goes back to step 26 .

FIG. 3 shows a corresponding timing diagram. First, the subscriber Tn 2 is the bus master and ring master of the arbitration ring 12 . The ring output at the output 18 of the subscriber Tn 2 is at logic 1, ie "bus / ring released". At the beginning of the bus clock 34 , the subscriber Tn 1 receives an access request to the data bus 10 , ie the signal Busreq_Tn 1 goes from logic 0 to logic 1; Likewise, the subscriber Tn 4 receives an access request to the data bus 10 , so that the signal Busreq_Tn 4 also goes from logic 0 to logic 1.

Since the "bus / ring released" signal circulates on the arbitration ring 12 and the subscriber Tn 1 receives this at its input 16 , the subscriber Tn 1 then outputs the "bus / ring" signal at its output 18 , ie in its ring output busy". The same applies to subscriber Tn 4.

The signals "Bus / Ring busy" output by the subscribers Tn 1 and Tn 4 then begin to propagate clockwise through the arbitration ring 12 via the individual subscribers. At the end of the bus clock 34 , the subscribers Tn 1 and Tn 4 each check at their inputs 16 whether the signal at the respective inputs 16 is still "bus / ring enabled".

This is the case for subscriber Tn 4, since it is arranged clockwise closer to ring master Tn 2, which is still current, in arbitration ring 12 . In contrast, "bus / ring occupied" is already present at input 16 of subscriber Tn 1. As a result, the subscriber Tn 4 becomes the new bus master and at the same time also the new ring master of the arbitration ring 12 and can access the data bus 10 .

FIG. 4 shows a corresponding situation in which the subscriber Tn 4 deactivates his bus request, ie switches back at his output 16 from "bus / ring occupied" to "bus / ring released". After subscriber Tn 4 has thus processed his access request or the maximum access time has expired, subscriber Tn 1 now has a turn and becomes the new bus and ring master.

FIG. 5 shows a situation in which the previous ring and bus master Tn 1 disables its bus request and first bus and ring master remains because no bus request of another user is active.

Fig. 6 shows an alternative embodiment of a communication system according to the invention with several Arbitrierungsringen.

The communication system includes subscribers 1, 2, 3, 4, 5 and 6 as well as data bus 10 . Participants 1 to 6 have arbitration modules 36 which are coupled to one another by arbitration rings 38 , 40 and 42 . The arbitration ring 38 is used to process access requests to the bus 10 with the highest priority 1. Accordingly, the arbitration ring 40 serves for access requests of priority 2 and the arbitration ring 42 for access requests of priority 3.

Fig. 6 shows the state of this communication system after a reset, said subscriber 2 is the bus master and at the same time, the ring master of Arbitrierungsringe 38, 40 and 42.

The flowchart of FIG. 7 illustrates the operation of a communication system of the type shown in FIG. 6 with a number of N priorities and a number of N arbitration rings.

In step 50 , one of the subscribers X of the communication system is bus master and ring master of the arbitration rings. This is the initial state after a reset. In step 52 , subscriber X applies the "bus / ring enabled" signal to the lowest-priority ring of the communication system, ie to arbitration ring 42 in the example in FIG. 6. This corresponds to step 22 of the embodiment in FIG. 2.

In step 54 , the subscriber Y of the communication system has an access request to the data bus 10 with priority i, where 1 ≤ i N. N. This step corresponds to step 24 in the embodiment in FIG. 2.

In step 56, the subscriber Y checks whether the "ring released" signal is present on the arbitration ring assigned to priority i at the input of the subscriber Y. If this is not the case, subscriber Y must wait until this condition is met. If the condition is fulfilled, however, the subscriber Y outputs the signal "ring occupied" at its output on the arbitration ring of priority i, for example at the beginning of a bus cycle.

In step 60, subscriber Y checks whether the "ring released" signal is still present at the input of subscriber Y for the arbitration ring of priority i at the end of the bus cycle. If this is not the case, the flow control of subscriber Y goes back to step 56 .

If the condition is met, step 62 is then carried out. Steps 56 , 58 and 60 correspond to steps 26 , 28 and 30 of the embodiment in FIG. 2, the arbitration ring which is assigned to priority i taking the place of the single arbitration ring 12 (cf. FIG. 1).

In step 62 , subscriber Y becomes the new ring master of the arbitration ring of priority i. However, subscriber Y has not yet become the bus master.

For this purpose, the user Y must first check in step 64 whether the signal "Ring occupied" on the arbitration ring with the lowest priority N or an arbitration ring with a priority that is greater than priority i at one of the arbitration ring inputs of the subscriber Y is present. If this is the case, subscriber Y must wait until the signal "Ring occupied" is replaced by "Ring released".

Then, in step 66, subscriber Y will output the "ring occupied" signal on the low-priority ring in order to then become the new bus master and ring master of the low-priority ring in step 68 .

FIG. 8 shows the state of the communication system of FIG. 6 when subscriber 2 is initially bus master and subscriber 3 has an access request to data bus 10 with priority 3 ("request priority 3") and subscriber 4 also has one Has request priority 2 and subscriber 5 has a request priority 1. In this situation, the subscriber 5 becomes the new ring master of the arbitration ring 38 of priority 1; subscriber 4 becomes the new ring master of arbitration ring 40 of priority 2 and subscriber 5 becomes new ring master of arbitration ring 42 of priority 3, although a request priority 3 is active for subscriber 3.

Participant 3 could only be the new ring master of priority 3 if there is no access request with a higher one Priority is active. After that, the participant always becomes the ring master priority 3, the bus request with the highest Priority. Each ring master is priority 3 at the same time also data bus master. Therefore the Participant 5 the new bus master.

FIG. 9 shows the state of the communication system based on the state of FIG. 8, ie the starting point that the subscriber 5 is the bus master. The participant 5 deactivates his request priority 1, the participant 3 having a request priority 3 and the participant 4 having a request priority 2. In this case, the subscriber 5 remains the ring master of the arbitration ring 38 of priority 1, since no other subscriber has activated an access request to the data bus 10 of priority 1. In addition, the subscriber 4 remains the ring master of the arbitration ring 40 of priority 2 and becomes the new ring master of the arbitration ring 42 of priority 3, although a request priority 3 is active for subscriber 3.

Participant 3 could only be the new ring master of priority 3 if no request with a higher priority is active. With this procedure, the participant is always the ring master of the Priority 3, the bus request with the highest priority has asked. Each ring master is priority 3 at the same time also data bus master. Therefore participant 4 is now the new busmaster.

Fig. 10 shows the state of the communication system, wherein the subscriber 4 is the old bus master. This deactivates his request priority 2. The participant 3 has a request priority 3. In this situation, the participant 5 remains the ring master of the arbitration ring 38 of priority 1, since no other participant has activated a request of priority 1. The subscriber 4 remains the ring master of the arbitration ring 40 of priority 2, since no other subscriber has activated a request of priority 2. The subscriber becomes the new ring master of the arbitration ring 42 of priority 3, since no request of a higher priority is active.

With this procedure, the participant is always the ring master of the Priority 3, the bus request with the highest priority has asked. Each ring master is priority 3 at the same time also data bus master. Therefore the participant is now 3rd the new bus master.

Fig. 11 shows the state of the communication system, in which the subscriber 4 activates a request priority 3 and the subscriber 6 its request priority 2 activated. In this situation, subscriber 6 immediately becomes the new ring master of the arbitration ring of priority 2. This is independent of the point in time at which the previous bus master, ie subscriber 3, deactivated his bus request.

However, subscriber 6 can become bus master at the earliest if the previous bus master, d. H. the participant 3, the Bus request deactivated. The priority of the bus request from Busmaster does not matter here.

As soon as the previous bus master, subscriber 3, receives the request Priority 3 deactivated, participant 6 becomes the new ring master of the Priority 3 and thus the new bus master.

Despite activated request priority 3, subscriber 4 does not become the ring master of priority 3, since a request of a higher priority is active. After the previous bus master, subscriber 3, has deactivated his bus request, the situation in FIG. 11 results.

Activates z. B. Participant 2 the request priority 3 before the current bus master subscriber 6 is ready to deliver the bus (i.e. his bus request deactivated), subscriber 2 becomes the new priority 3 ring masters and thus new bus master, when participant 6 deactivates the bus request and for this No other request with a higher priority at the time Participant is activated. Participant 4 has earlier than Participant 2 bus request priority 3 activated, but was at Busmaster change from subscriber 3 to subscriber 6 skipped.

Activates e.g. B. Participants 5 bus request priority 1 or Bus request priority 2 before the current bus master, participant 2, is ready to deliver the bus, will be the next bus master change Participant 4 again not considered. The reason that when changing the bus master, a participant who low priority bus request is activated, is not taken into account of that the ringmaster in this lowest priority this method is always the bus master.

To overcome this disadvantage, disregarding one Avoiding the participant when changing the bus master is above to modify the described method so that in addition to A bus master ring is introduced into the N priority rings. With 3 priorities, 4 rings are necessary: 3 Priority rings and 1 bus master ring. In contrast to the above described procedure, the lowest priority ring behaves analogously to the higher priority rings. Busmaster is in this process the ringmaster of the busmaster ring.

The advantage of the two methods presented is that Minimize the waiting time of a participant who has a high priority Busrequest has put on the bus allocation. disadvantage Both procedures involve the possibility of long waiting times Participants who made a low priority bus request if there are many high priority bus requests from queue up to other participants.

Another arbitration procedure based on the ring structure based, has the advantages of the two above methods, while reducing their disadvantages.

• - N Prioritätsringe, die analog zu den oben beschriebenen funktionieren, wobei N ≥ 2 ist,
• - einen virtuellen Teilnehmer im Prioritätsring (N-1), der die Teilnehmer im Prioritätsring der Priorität N repräsentiert. N ist die niedrigste Priorität,
• - einen virtuellen Teilnehmer im Prioritätsring (N-2), der die Teilnehmer im Prioritätsring der Priorität (N-1) repräsentiert,
• - einen virtuellen Teilnehmer im Prioritätsring (N-3), der die Teilnehmer im Prioritätsring der Priorität (N-2) repräsentiert,
• - etc.
• - einen virtuellen Teilnehmer im Prioritätsring 1, der die Teilnehmer im Prioritätsring der Priorität 2 repräsentiert,
• - jeder virtuelle Teilnehmer eines Arbitrierungsringes muss immer dann, wenn ein Teilnehmer des repräsentierten Ringes zur Busabgabe bereit ist, einen Teilnehmer seiner oder einer höheren Prioritätsebene das Buszugriffsrecht überlassen,
• - Datenbus-Master ist immer der Ringmaster des Arbitrierungsringes mit der höchsten Priorität.

This arbitration procedure is characterized by

• N priority rings, which function analogously to those described above, where N ≥ 2,
• - A virtual participant in the priority ring (N-1), which represents the participants in the priority ring of priority N. N is the lowest priority,
• a virtual subscriber in the priority ring (N-2), which represents the subscribers in the priority ring of priority (N-1),
• a virtual subscriber in the priority ring (N-3), which represents the subscribers in the priority ring of priority (N-2),
• - Etc.
• a virtual participant in priority ring 1, which represents the participants in priority ring of priority 2,
• each virtual subscriber of an arbitration ring must grant the bus access right to a subscriber of his or a higher priority level whenever a subscriber of the represented ring is ready for bus delivery,
• - The data bus master is always the ring master of the arbitration ring with the highest priority.

FIG. 12 shows a block diagram of an exemplary embodiment of such a communication system with an arbitration method with N = 3, ie for three priorities and three arbitration rings.

The arbitration ring 44 is assigned to priority 1 and connects the arbitration modules 14 of the participants' priority 1 with one another and the arbitration module 50 of an arbitration unit, which is referred to below as a virtual subscriber. The arbitration module 50 represents the arbitration modules 14 of priority 2 in the arbitration ring 44 of priority 1. If there is an access request to the data bus with priority 2 in one of the participants, this is done by the arbitration module 50 in the arbitration ring 44 of priority 1 by a Priority 1 access request represented.

The same applies to the arbitration module 52 in the arbitration ring 46 , which represents access requests of the participants with priority 3 in the arbitration ring 46 of priority 2.

The data bus master is always the ring master of the arbitration ring with the highest priority. When changing the ring master, the corresponding timing diagrams in FIGS. 3 to 5 continue to apply for each arbitration ring.

Figs. 12 shows the state after reset: The participant 2 is bus master, as long as no bus request is activated.

FIG. 13 uses a flow chart to illustrate the mode of operation of a communication system of the type of FIG. 12. In step 60 , one of the subscribers Y has an access request to the data bus with priority i. In step 62 , this access request is represented by the virtual subscriber of priority i-1 in the arbitration ring of priority i-1 by a corresponding access request of priority i-1.

In step 64 , the virtual subscriber of priority i-1 becomes the ring master in the arbitration ring of priority i-1. Furthermore, the virtual subscriber also becomes bus master (step 66 ), so that subscriber Y can access the bus in step 68 .

Fig. 14 shows the state of the communication system when initially the subscriber 2 is the old bus master. In the same bus cycle, subscriber 3 activates a request priority 3, subscriber 1 a request priority 2 and subscriber 4 a request priority 1. The subscriber 3 then becomes the new ring master of the arbitration ring 48 of priority 3; the virtual subscriber with the arbitration module 52 becomes the new ring master of the arbitration ring 46 of priority 2; the virtual subscriber with the arbitration module 50 becomes the new ring master of the arbitration ring 44 of priority 1 and the subscriber 3 finally receives access to the data bus 10 .

In the Fig. 15 of the subscriber 3 is the current bus master. Participant 2 activates request priority 3.

• - Teilnehmer 2: Request-Prio 3 ist aktiv;
• - Teilnehmer 1: Request-Prio 2 ist aktiv;
• - Teilnehmer 4: Request-Prio 1 ist aktiv;
• - Teilnehmer 2 wird neuer Ringmaster des Arbitrierungsrings der Priorität 3;
• - Teilnehmer 1 wird neuer Ringmaster des Arbitrierungsrings der Priorität 2;
• - Teilnehmer 4 wird neuer Ringmaster des Arbitrierungsrings der Priorität 1;
• - Teilnehmer 4 wird der neue Datenbus-Master.

The following bus requests are thus active when the current bus master subscriber 3 is ready to change the bus master:

• - Participant 2: Request priority 3 is active;
• - Participant 1: Request priority 2 is active;
• - Participant 4: Request priority 1 is active;
• - Subscriber 2 becomes the new ring master of the arbitration ring with priority 3;
• - Subscriber 1 becomes the new ring master of the arbitration ring with priority 2;
• - Participant 4 becomes the new ring master of the arbitration ring with priority 1;
• - Participant 4 becomes the new data bus master.

. In Fig 16 participants is 4 current bus master; Participant 3 activates request priority 1.

• - Teilnehmer 2: Request-Prio 3 ist aktiv;
• - Teilnehmer 1: Request-Prio 2 ist aktiv;
• - Teilnehmer 3: Request-Prio 1 ist aktiv;
• - Teilnehmer 2 bleibt Ringmaster des Arbitrierungsrings der Priorität 3;
• - Teilnehmer 1 bleibt Ringmaster des Arbitrierungsrings der Priorität 2;
• - virtueller Teilnehmer-P2 wird neuer Ringmaster des Arbitrierungsrings der Priorität 1;
• - Teilnehmer 1 wird der neue Datenbus-Master.

The following bus requests are active when the current bus master subscriber 4 is ready to change the bus master:

• - Participant 2: Request priority 3 is active;
• - Participant 1: Request priority 2 is active;
• - Participant 3: Request priority 1 is active;
• Subscriber 2 remains ring master of the arbitration ring of priority 3;
• - Subscriber 1 remains the ring master of the priority 2 arbitration ring;
• - virtual subscriber P2 becomes the new ring master of the arbitration ring of priority 1;
• - Subscriber 1 becomes the new data bus master.

. In Fig 17 participants is 1 Current bus master:

• - Teilnehmer 2: Request-Prio 3 ist aktiv;
• - Teilnehmer 3: Request-Prio 1 ist aktiv;
• - Teilnehmer 2 bleibt Ringmaster des Arbitrierungsrings der Priorität 3;
• - virtueller Teilnehmer-P3 wird neuer Ringmaster des Arbitrierungsrings der Priorität 2;
• - Teilnehmer 3 wird neuer Ringmaster des Arbitrierungsrings der Priorität 1;
• - Teilnehmer 3 wird der neue Datenbus-Master.

The following bus requests are thus active when the current bus master subscriber 1 is ready to change the bus master:

• - Participant 2: Request priority 3 is active;
• - Participant 3: Request priority 1 is active;
• Subscriber 2 remains ring master of the arbitration ring of priority 3;
• - virtual subscriber P3 becomes the new ring master of the arbitration ring of priority 2;
• - Participant 3 becomes the new ring master of the arbitration ring of priority 1;
• - Participant 3 becomes the new data bus master.

In FIG. 18, subscriber 3 is the current bus master:

• - Teilnehmer 2: Request-Prio 3 ist aktiv;
• - Teilnehmer 2 bleibt Ringmaster des Arbitrierungsrings der Priorität 3;
• - virtueller Teilnehmer-P3 bleibt Ringmaster des Arbitrierungsrings der Priorität 2;
• - virtueller Teilnehmer-P2 wird neuer Ringmaster des Arbitrierungsrings der Priorität 1;
• - Teilnehmer 2 wird der neue Datenbus-Master.

The following bus requests are thus active when the current bus master subscriber 3 is ready to change the bus master:

• - Participant 2: Request priority 3 is active;
• Subscriber 2 remains ring master of the arbitration ring of priority 3;
• virtual subscriber P3 remains ring master of the arbitration ring of priority 2;
• - virtual subscriber P2 becomes the new ring master of the arbitration ring of priority 1;
• - Subscriber 2 becomes the new data bus master.

• - Teilnehmer 2 bleibt Ringmaster des Arbitrierungsrings der Priorität 3;
• - virtueller Teilnehmer-P3 bleibt Ringmaster des Arbitrierungsrings der Priorität 2;
• - virtueller Teilnehmer-P2 bleibt Ringmaster des Arbitrierungsrings der Priorität 1;
• - Teilnehmer 2 bleibt Datenbus-Master, bis ein anderer Teilnehmer einen Busrequest aktiviert.

. In Fig 19 participants 2 is the current bus master:
This means that no bus requests are active if the current bus master subscriber 3 is ready to change the bus master:

• Subscriber 2 remains ring master of the arbitration ring of priority 3;
• virtual subscriber P3 remains ring master of the arbitration ring of priority 2;
• - virtual subscriber P2 remains ring master of the arbitration ring of priority 1;
• - Participant 2 remains the data bus master until another participant activates a bus request.

Claims (9)

1. A method for arbitrating access to a data bus between subscribers (Tn1, Tn2,...), The subscribers being coupled by at least one arbitration ring ( 12 ; 38 , 40 , 42 , 44 , 46 , 48 ), with the following steps : a) requesting access by a first of the participants, b) checking whether a first signal to indicate that the arbitration ring is released is present at an input ( 16 ) of the first participant, c) output ( 18 ) of a second signal by the first subscriber when the first signal is present, d) checking whether the first signal is still present at the input of the first subscriber at the end of a predetermined time interval, e) Access by the first participant if the first signal was still present at the end of the predetermined time interval. 2. A method for arbitrating access to a data bus between subscribers (Tn1, Tn2,...), The subscribers being coupled by a number of arbitration rings ( 12 ; 38 , 40 , 42 , 44 , 46 , 48 ) and each Arbitration ring is assigned a priority, with the following steps: a) requesting access by a first of the participants with a first priority, b) checking whether a first signal for indicating that the arbitration ring assigned to the first priority is released is present at an input ( 16 ) of the first participant, c) output ( 18 ) of a second signal on the arbitration ring assigned to the first priority by the subscriber if the first signal was present at the input, d) checking whether the first signal is still present at the input at the end of a predetermined time interval, e) checking whether the second signal is present at an input of the subscriber for the lowest-priority arbitration ring or at an input of the subscriber for an arbitration ring that is assigned a higher priority than the first priority, f) output of the second signal on the low-priority ring, g) Access of the first participant. 3. The method according to claim 2, comprising a virtual subscriber ( 50 , 52 ) for representing access requests of the subscribers of a second priority in an arbitration ring which is assigned a higher third priority. 4. The method of claim 1, 2 or 3, wherein it is predetermined time interval around a bus clock of the data bus is. 5. Participants for access to a data bus ( 10 ) and for coupling to an arbitration ring ( 38 , 40 , 42 , 44 , 46 , 48 ) with: a) means for requesting access, b) means for checking whether a first signal for indicating that the arbitration ring is released is present at an input ( 16 ) of the first participant, c) means for the output ( 18 ) of a second signal by the first subscriber when the first signal is present, d) means for checking whether the first signal is still present at the input of the first subscriber at the end of a predetermined time interval, e) means for access by the first participant if the first signal was still present at the end of the predetermined time interval. 6. Participants for access to a data bus ( 10 ) and for coupling with a number of arbitration rings ( 38 , 40 , 42 , 44 , 46 , 48 ), with each arbitration ring being assigned a priority with a) means for requesting access from a first of the participants with a first priority, b) means for checking whether a first signal for indicating that the arbitration ring assigned to the first priority is enabled is present at an input ( 16 ) of the first subscriber, c) means for the subscriber to output ( 18 ) a second signal on the arbitration ring assigned to the first priority if the first signal was present at the input, d) means for checking whether the first signal is still present at the input at the end of a predetermined time interval, e) means for checking whether the second signal is present at an input of the subscriber for the low-priority arbitration ring or at an input of the subscriber for an arbitration ring which is assigned a higher priority than the first priority, f) means for outputting the second signal to the low-priority ring, g) means for access by the first participant. 7. Arbitration unit providing a virtual subscriber for arbitrating access to a data bus ( 10 ) between subscribers, the subscribers being coupled by a number of arbitration rings ( 38 , 40 , 42 , 44 , 46 , 48 ), and a priority for each arbitration ring is assigned, with means ( 50 , 52 ) for representing access requests of the subscribers of a second priority in an arbitration ring which is assigned to a higher third priority. 8. Participant according to one of the preceding claims 5, 6 or 7, wherein the predetermined time interval is a bus cycle ( 34 ). 9. Communication system with several participants, each participant being designed according to one of the preceding claims 5 to 8, and with one or more of the arbitration rings ( 38 , 40 , 42 , 44 , 46 , 48 ) for coupling the participants.