JP3646672B2 - Cyclic data communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cyclic data communication system suitable for applications such as a data link in a PLC system, and in particular, a scheduled communication phase (for example, an isochronous communication phase) and an asynchronous communication phase (for example, an asynchronous communication phase) such as an IEEE 1394 bus. In addition, the present invention relates to a novel cyclic data communication system that enables high-speed cyclic data communication with guaranteed transmission timing and maximum transmission amount of each communication node.
[0002]
[Prior art]
PLC systems incorporating a data link function are well known in the art. In such a PLC system, a plurality of programmable logic controllers (hereinafter referred to as PLCs) are connected by a serial bus, and I / O data and the like are periodically exchanged with each other, while the I / O in the entire system is performed. Sharing of data is realized.
[0003]
That is, in this type of PLC system, not only the I / O data area of the own machine but also the I / O data area of the other machine is provided in the memory of each PLC. In each PLC arithmetic unit (commonly called CPU unit), I / O refresh processing, instruction execution processing, and peripheral service processing are executed cyclically at all times. In the peripheral service processing, each PLC transmits the contents of its own I / O data area to other machines, for example, while broadcasting the I / O data broadcast to each other machine. Then, it is stored in the corresponding I / O data area for the other device. As each PLC sequentially operates in the same manner, the contents of the I / O data area of the other machine in the memory in each PLC are periodically updated. As a result, the I / O data in the memory of each machine is Automatically linked to each other.
[0004]
In recent years, the number of control points handled by the PLC has increased dramatically. Therefore, a serial bus required for realizing the data link function is required to be capable of high-speed and large-capacity transmission.
[0005]
In addition, in the trend of market liberalization and internationalization, recently, control system components tend to be mixed from various manufacturers. Therefore, the serial bus required for realizing the data link function is required to have an open standard rather than a specification unique to each manufacturer.
[0006]
[Problems to be solved by the invention]
For example, an IEEE 1394 bus is known as an open standardized serial bus capable of high-speed and large-capacity transmission. The IEEE 1394 bus is provided with an isochronous communication phase and an asynchronous communication phase.
[0007]
In the isochronous communication phase, an arbitration function operates so as to sequentially give transmission opportunities to each communication node while guaranteeing transmission every time within the isochronous cycle (125 μs) for all communication nodes that have issued transmission requests. .
[0008]
In the asynchronous communication interface, each communication node is sequentially given a transmission opportunity while guaranteeing the maximum value of the transmission data amount in the remaining period after the completion of the isochronous phase in the isochronous cycle for the communication node that has issued the transmission request. The arbitration function works as given.
[0009]
However, since the IEEE 1394 bus is mainly used for real-time transmission of digital video data or the like, the amount of data per communication node that can be transmitted on a regular basis is relatively small. When applied to data transfer for realization, there is a problem that the transmission data becomes fragmented and the data transmission speed cannot be sufficiently increased.
[0010]
The present invention has been made paying attention to the above-mentioned problems, and the object of the present invention is, for example, a regular communication phase (corresponding to an isochronous communication phase) and an asynchronous communication phase (asynchronous communication phase) as in the IEEE 1394 bus. In other words, cyclic data transmission having a fixed time system is possible while guaranteeing the maximum transmission data amount of each communication node.
[0011]
Another object of the present invention is to provide a PLC system capable of realizing a data link function while transmitting a relatively large amount of I / O data or the like between PLCs at high speed. .
[0012]
Another object of the present invention is to control a high response while transmitting a relatively large amount of I / O data between a master PLC and a plurality of slave input / output devices at high speed. Is to provide a remote I / O system for PLC.
[0013]
Furthermore, other objects and operational effects of the present invention will be easily understood by those skilled in the art by referring to the description in the following specification.
[0014]
[Means for Solving the Problems]
The cyclic data transmission system of the present invention is configured by connecting a plurality of communication nodes with a serial bus having a unique communication cycle.
[0015]
The serial bus has a regular communication phase and an asynchronous communication phase.
[0016]
In the regular communication phase, the arbitration function operates so that all communication nodes that have issued transmission requests are given transmission opportunities to each communication node sequentially while guaranteeing transmission every time for a specific communication cycle.
[0017]
In the asynchronous communication phase, to the communication node that issued the transmission request, transmission is sequentially made to each communication node while guaranteeing the maximum value of the transmission data amount in the remaining period excluding the scheduled communication phase in the specific communication cycle. The mediation function acts to give an opportunity.
[0018]
At least one of the plurality of communication nodes is assigned to the management station, and the other communication nodes are assigned to the normal station.
[0019]
The communication node assigned to the management station periodically transmits a cyclic trigger code indicating the start of a communication cycle in the regular communication phase.
[0020]
The communication node assigned to the normal station issues a transmission request in the asynchronous communication phase in response to detecting the cyclic trigger code transmitted from the communication node assigned to the management station in the regular communication phase. By obtaining the transmission opportunity, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the communication node which is another station is received.
[0021]
As a result, the cyclic communication is performed cyclically while using the asynchronous communication phase between the communication nodes over a plurality of unique communication cycles using the transmission cycle of the cyclic trigger code as a data communication cycle.
[0022]
According to such a configuration, for example, a standardized serial bus having both a regular communication phase (corresponding to an isochronous communication phase) and an asynchronous communication phase (corresponding to an asynchronous communication phase), such as an IEEE1394 bus, is assumed. As described above, cyclic data transmission having punctuality can be performed while guaranteeing the maximum transmission data amount of each communication node.
[0023]
As a cyclic data transmission system in a more preferred embodiment of the present invention, a plurality of communication nodes may be connected by an IEEE 1394 bus.
[0024]
The IEEE 1394 bus includes an isochronous communication phase and an asynchronous communication phase.
[0025]
In the isochronous communication phase, an arbitration function is provided so that each communication node is sequentially given a transmission opportunity while guaranteeing transmission every isochronous communication cycle (for example, 125 μs) to all communication nodes that have issued transmission requests. Works.
[0026]
In the asynchronous communication phase, each communication node is sequentially given a transmission opportunity while guaranteeing the maximum value of the amount of transmission data for the remaining period after the completion of the isochronous phase in the isochronous cycle for the communication node that issued the transmission request. The arbitration function works as given.
[0027]
At least one of the plurality of communication nodes is assigned to the management station, and the other communication nodes are assigned to the normal station.
[0028]
In the isochronous communication phase, the communication node assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle.
[0029]
The communication node assigned to the normal station issues a transmission request in the asynchronous communication phase in response to detecting a cyclic trigger packet transmitted from the communication node assigned to the management station in the isochronous communication phase. By obtaining the transmission opportunity, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the communication node which is another station is received.
[0030]
The management station may concentrate on management, or may transmit its own data after transmitting the cyclic trigger packet.
[0031]
As a result, the cyclic trigger packet transmission cycle is used as a data communication cycle, and cyclic data communication is performed between the communication nodes using the asynchronous communication phase across a plurality of isochronous communication cycles.
[0032]
According to such a configuration, assuming that the IEEE1394 bus having both the isochronous communication phase and the asynchronous communication phase is used, a maximum transmission data amount (for example, a maximum of 62 μs) per communication node is guaranteed. Thus, cyclic data transmission having punctuality can be performed.
[0033]
Incidentally, the transmission data for 62 μs corresponds to 512 bytes in the case of 100 Mbps, 1024 bytes in the case of 200 Mbps, and 2048 Mbyte in the case of 400 Mbps.
[0034]
In a preferred embodiment of the present invention, the transmission timing of the cyclic trigger packet may be obtained by calculation based on the total amount of transmission data per scheduled communication cycle.
[0035]
According to such a configuration, it is possible to perform cyclic data communication with the shortest cycle time while reliably guaranteeing a transmission opportunity and a transmission data amount for all communication nodes scheduled for transmission.
[0036]
In a preferred embodiment of the present invention, the transmission timing of the cyclic trigger packet may be determined by interruption of transmission data in the asynchronous communication phase.
[0037]
According to such a configuration, every communication opportunity is always guaranteed for all communication nodes even when the number of communication nodes that issue a transmission request varies depending on the execution status of the application. However, cyclic data communication is possible.
[0038]
The PLC system of the present invention is configured by connecting a plurality of PLCs with an IEEE 1394 bus.
[0039]
The IEEE 1394 bus includes an isochronous communication phase and an asynchronous communication phase.
[0040]
In the isochronous communication phase, the arbitration function works so as to provide each communication node with a transmission opportunity in order while guaranteeing transmission every isochronous cycle (for example, 125 μs) for all communication nodes that have issued transmission requests. To do.
[0041]
In the asynchronous communication phase, with respect to the communication node that issued the transmission request, in the remaining period after the end of the isochronous communication phase in the isochronous cycle, each communication node is assured the maximum value (for example, 62 μs) of the transmission data amount. On the other hand, an arbitration function for sequentially providing transmission opportunities operates.
[0042]
At least one of the plurality of PLCs is assigned to the management station, and the other PLC is assigned to the normal station.
[0043]
The PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase.
[0044]
In response to detecting a cyclic trigger packet transmitted from the control station PLC in the isochronous communication phase, the PLC assigned to the normal station issues a transmission request and obtains a transmission opportunity in the asynchronous communication phase. Thus, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the PLC which is another station is received.
[0045]
As a result, the cyclic trigger packet transmission cycle is used as a data communication cycle, and the control data is linked to each other by performing cyclic data communication between the PLCs while using the asynchronous communication phase. Here, the control data may include input data such as relays, switches, and sensors to be controlled, and output data such as actuators. These are often binary data on and off. Data links other than binary data may be used, for example, analog input numerical values and analog input numerical values to be controlled, or production information (production quantity, operating time, number of errors, etc.).
[0046]
According to such a configuration, it is possible to realize a PLC system in which a large amount of I / O data or the like is closely linked between PLCs with high response.
[0047]
The PLC remote I / O system according to the present invention is configured by connecting one PLC and a plurality of input / output devices via an IEEE 1394 bus.
[0048]
The IEEE 1394 bus includes an isochronous communication phase and an asynchronous communication phase.
[0049]
In the isochronous communication phase, there is an arbitration function for sequentially giving a transmission opportunity to each communication node while guaranteeing transmission every isochronous communication cycle (for example, 125 μs) to all communication nodes that have issued transmission requests. Works.
[0050]
In the asynchronous communication phase, each communication node guarantees the maximum transmission data amount (for example, 62 μs) in the remaining period after the end of the isochronous communication phase in the isochronous communication cycle for the communication node that has issued the transmission request. An arbitration function for sequentially giving transmission opportunities to the network operates.
[0051]
The PLC is assigned to the management station, and each of the plurality of input / output devices is assigned to the normal station.
[0052]
The PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase.
[0053]
In response to detecting the cyclic trigger packet transmitted from the control station PLC in the isochronous communication phase, the input / output device assigned to the normal station issues a transmission request in the asynchronous communication phase and transmits a transmission opportunity. Thus, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the PLC as the management station is received.
[0054]
In this example, the management station is a PLC and the normal station is an input / output device. However, in terms of the protocol, anyone may be the management station. Even if it is a management station, it does not manage anything but only plays a role of periodically sending trigger packets.
[0055]
As a result, the cyclic trigger packet transmission cycle is used as a data communication cycle, and cyclic data communication is performed between the PLC and each input / output device using the asynchronous communication phase. Link the data.
[0056]
According to such a configuration, a large number of controlled devices can be controlled with high response by a single PLC via a plurality of remote input / output devices.
[0057]
In a preferred embodiment in each of the above systems, the transmission timing of the cyclic trigger packet may be obtained by calculation based on the total amount of transmission data per scheduled communication cycle.
[0058]
In a preferred embodiment in each of the above systems, the transmission timing of the cyclic trigger packet may be determined by transmission data interruption in the asynchronous phase.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
In the following, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0060]
First, in order to facilitate understanding of the present invention, basic items relating to IEEE 1394, which is an open standard serial bus, will be described. A time chart showing a standard transmission procedure of IEEE1394 is shown in FIG.
[0061]
In the IEEE 1394 data transfer, all nodes operate equally. The transfer operation of each node includes a case where transfer is performed by designating a specific node ID and a case where transfer is performed for all nodes (broadcast).
[0062]
In either case, when a plurality of nodes transmit data to the bus at the same time, a collision occurs. Therefore, only the node that has acquired the use right by performing arbitration in advance uses the bus. However, the usable time is limited to a relatively short time, and the next transmission is immediately switched. This is because it is possible to simultaneously transfer a plurality of real-time data by preventing the transmission of one node from occupying the bus for a long time and guaranteeing the bandwidth of the other transmission.
[0063]
There is only one root node in the bus, and the tree can be traced from the root to all nodes. An upstream node with respect to each node is a parent node, and the parent node can be sequentially traced to reach the root. The node requesting the right to use the bus issues a request to the parent node, and the request is collected in the route. The route gives usage rights so that each node is fair.
[0064]
The IEEE 1394 transfer method has two phases: an isochronous transfer phase in which the bandwidth is guaranteed and an asynchronous transfer phase in which the bandwidth is not guaranteed. In any phase, such arbitration is performed at the beginning of the transfer. In the case of the isochronous transfer phase, it is guaranteed that data transfer can be performed at least once every 125 μsec even if it is postponed by arbitration. On the other hand, in the asynchronous transfer phase, there may be a long wait depending on the result of arbitration.
[0065]
In the IEEE 1394 data transfer, a transfer cycle is repeated every 125 μsec, and a transfer time is allocated little by little to each node in each cycle. In the first half of the cycle, an isochronous transfer channel is allocated. Asynchronous transfers are assigned to the remaining time in the second half of the cycle.
[0066]
The start of the cycle will be described in detail. One of the nodes (generally the root) becomes the cycle master and manages the execution of the cycle. The cycle master broadcasts a cycle start packet every 125 μsec, so that each node knows the cycle start timing.
[0067]
The isochronous transfer will be described in detail. In order to prevent data collision, a node requesting isochronous transfer issues a request for channel use right after a certain time interval after the cycle start packet. This interval is called an isochronous gap. The node that has acquired the channel use right by arbitration continues to transfer data as an isochronous packet. After the end of one channel, arbitration of the next channel is performed with an isochronous gap, and the node that has acquired the right to use the channel transfers data as an isochronous packet. This is repeated sequentially until there are no more nodes requesting channel usage rights.
[0068]
Asynchronous transfer will be described in detail. When the last channel of isochronous transfer is completed, there is no node requesting the channel use right, and a free time occurs on the bus. A node requesting asynchronous transfer is permitted to issue a request for asynchronous transfer when it detects that the bus idle time has reached a certain time longer than the isochronous gap. This time is called the subaction gap. The node that has acquired the right to use the bus by arbitration subsequently transfers the data packet. After the end of one data packet, the next transfer is arbitrated with a subaction gap, and the node that has acquired the right to use the bus transfers the data packet. This is repeated until there is no node requesting the right to use the bus or the cycle time reaches 125 μsec.
[0069]
The end of the cycle will be described. If there is no node that requests the right to use the bus before the cycle time reaches 125 μsec, the remaining time of the cycle becomes a free time. On the other hand, when the cycle time becomes 125 μsec during the transfer of the data packet, the cycle master waits until the packet is transferred to the end and starts the next cycle. At this time, the time of the next cycle is shortened by the amount delayed, and the average cycle time is maintained at 125 μsec. To prevent the next cycle time from becoming too short, asynchronous transfer packets are limited to a maximum of 62 μsec.
[0070]
As described above, in IEEE1394, an isochronous packet (Isochronous Packet) is prepared for transmission of a synchronous message, and an asynchronous packet (Asynchronous Packet) is prepared for transmission of an asynchronous message. ing. The packet configurations of the isochronous packet and the asynchronous packet are the same.
[0071]
The isochronous packet is a synchronous packet and can be transmitted periodically by each node. The isochronous packet is transmitted by designating a channel ID (tag). Each station is provided with a channel ID filter, and only the channel ID packets that are permitted to be received by the filter are received.
[0072]
The transmission timing of asynchronous packets and asynchronous stream packets is not defined in IEEE 1394, and the decision is left to the application side. The asynchronous packet is transmitted by directly specifying the IEEE 1394 Phy_ID (physical ID / physical layer address), and the Phy_ID is received by the corresponding node.
[0073]
In IEEE 1394, data of all channels requested to be transmitted in an isochronous cycle is transmitted. In isochronous communication, all stations having requested transmission transmit isochronous data using a cycle start packet as a trigger. The cycle start packet is periodically transmitted every 125 μs. Thereby, cyclic communication can be performed. Further, in order to guarantee that all stations can transmit isochronous data, a register indicating a remaining bandwidth called BANDWIDTH_AVALABLE is provided to limit the time of isochronous phase and the amount of transmission data. Further, there is only one transmission of the same channel within one isochronous cycle, and two stations cannot transmit the same channel. This means that it guarantees that the necessary data can be transmitted reliably.
[0074]
By the way, it is obvious that isochronous communication defined by IEEE 1394 is preferably used to perform periodic data transfer (cyclic communication) in IEEE 1394.
[0075]
However, as described above, since transmission of all channels and all isochronous data within 125 μs is guaranteed, isochronous data that can be transmitted within one isochronous cycle has a maximum of 1536 bytes at 100 Mbps as shown in FIG. It will be limited to. If these 1536 bytes are transmitted by 63 stations and each station occupying one channel, it becomes 24 bytes per node. In this case, the use is extremely limited.
[0076]
For example, in an application such as a PLC system having a data link function, a plurality of PLCs share data of each station. At this time, each station broadcasts its own station data and receives the broadcast data of other stations to share data between PLCs. Such systems often share several kilobytes of data, and a transmission capacity of about 24 bytes per station is not sufficient in data capacity.
[0077]
Even if 24 bytes of data are assembled and large data is transmitted, the ratio of data not used in the application such as header and tailer included in the transmission data increases, the substantial transmission efficiency decreases, and high speed. The merit of using the transmission line is reduced.
[0078]
In addition, in a PLC system having a data link function, data punctuality is also important. That is, it is necessary to guarantee a transmission delay time when certain data is transferred.
[0079]
Even in IEEE 1394, the problem of data capacity can be solved by using an asynchronous packet, but in that case, punctuality cannot be guaranteed. There is no mechanism that allows each station to transmit data equally.
[0080]
Therefore, in the present invention, the problem of the amount of data is solved by transmitting cyclic data using an asynchronous message, and the problem of punctuality is solved by sending the transmission timing using a synchronous message.
[0081]
In this way, by appropriately adjusting the transmission timing of cyclic data, the data amount is not limited to 1536 bytes, and cyclic communication can be performed while maintaining punctuality.
[0082]
That is, an asynchronous stream packet that is an asynchronous message may be used for cyclic data transmission. Asynchronous stream packets use channels to specify destinations for transmission and reception in the same way as isochronous packets. The receiving side only needs to specify the channel, and the packet header is small, so data can be transmitted to all stations. Good. Of course, an asynchronous packet may be transmitted to the broadcast address. On the other hand, an isochronous packet may be used to notify the transmission timing of cyclic data. Thereby, it is possible to reliably give a cyclic data transmission trigger.
[0083]
More specifically, a management station and a normal station connected to IEEE 1394 may operate according to the following procedure.
[0084]
That is, the management station transmits an isochronous packet (cyclic trigger packet) that triggers cyclic data transmission.
[0085]
There are several possible methods for determining the timing for transmitting the cyclic trigger packet. As one method, the amount of cyclic data is determined in advance, and the period required for transmission is calculated from the data amount. The transmission timing of the cyclic trigger packet is determined based on the value. As another method, since the cyclic data is broadcast simultaneously, the packet is always monitored, and when no cyclic trigger data is received for a certain period of time, cyclic data transmission of all stations is performed. Is finished, the next cyclic trigger packet is transmitted. That is, when the transmission of cyclic data is interrupted for a certain time, it is determined that the transmission timing of the cyclic trigger bucket has arrived.
[0086]
There are several possible methods for determining the management station. As one method, a node to be a management station is determined in advance. As another method, the management station is the one with the largest or smallest Phy_ID. Furthermore, as another method, an isochronous resource manager (a node having a register such as BANDWIDTH_AVALABLE described above) serves as a management station.
[0087]
On the other hand, the normal station monitors the reception of the cyclic trigger packet. As soon as the cyclic trigger packet is received, the cyclic data of the own station is transmitted. It also receives cyclic data from other stations. The cyclic trigger packet from the management station is monitored, and if it cannot be received for a certain period of time, it is determined that an abnormality has occurred and the management station is re-determined.
[0088]
Next, a specific example of a cyclic data communication system to which the present invention is applied will be described in detail with reference to FIGS.
[0089]
An explanatory diagram showing the relationship between the serial bus (IEEE1394 in this example) and each communication node is shown in FIG. As shown in the figure, this cyclic data communication system is configured by connecting N (plural) communication nodes Node1 to NodeN with a bus BUS defined by IEEE1394. As a method of connection, in addition to a daisy chain shape or a tree shape, a mixed form thereof can be adopted. As a signal line constituting the bus, for example, a twisted pair line or the like can be used. In particular, in this example, Node 1 is assigned to the management station, and Node 2 to Node N are assigned to the normal station.
[0090]
A block diagram schematically showing the hardware configuration of each of the communication nodes Node1 to NodeN is shown in FIG. As shown in the figure, a circuit device (generally embodied as a communication board or the like) 400 constituting each communication node 400 realizes a data transmission / reception function with a signal line constituting a serial bus Bus. Communication controller 401, CPU 402 that performs overall control of the entire circuit device, ROM 403 that stores an operation program and the like of the microprocessor that constitutes CPU 402, RAM 404 that functions as a work area for the operation of CPU 402, and temporary storage of transmission / reception data A transmission / reception buffer 405 functioning as a region and an isochronous resource register (including BANDWIDTH_AVAILABLE) 406 are included.
[0091]
FIG. 5 is a flowchart showing processing on the management station side, and FIG. 6 is a flowchart showing processing on the normal station side. Hereinafter, the operation of the cyclic data communication system of the present invention will be systematically described with reference to these flowcharts and the time charts of FIGS.
[0092]
First, as shown in the flowchart of FIG. 5, the communication node Node1 serving as the management station enters a state of waiting for a predetermined timer to expire (step 501 NO). This timer specifies the transmission cycle of the cycle trigger packet. As a method for determining the timer time, as described above, the amount of cyclic data is determined in advance, and the period necessary for transmission is calculated from the data amount. The transmission timing of the cyclic trigger packet is determined based on the value.
[0093]
When the timer expires (step 501 YES), a cyclic trigger packet transmission process prepared in advance is executed (step 502). Thereby, on the serial bus Bus, for example, a cyclic trigger packet is transmitted as an isochronous communication packet to all other communication nodes (see the explanatory diagram of FIG. 3). The transmission of the cyclic trigger packet performed as the isochronous communication packet can be realized by, for example, broadcast simultaneous transmission or all channel designation. As described above, this cyclic trigger packet informs the other communication nodes Node2 to NodeN, which are normal stations, of the start time of each communication cycle in the cyclic data communication intended by the application. belongs to.
[0094]
Following the transmission of the cyclic trigger packet, the communication node Node1 serving as the management station determines whether or not there is a transmission data request from its own station, and if the transmission request is also from its own station The local cyclic data bucket is transmitted (step 503). Thereby, on the serial bus Bus, the cyclic data packet from the management station is transmitted to the determined partner station as an asynchronous communication packet. If there is no cyclic data transmission request from the own station, the data transmission process (step 503) from the own station is skipped.
[0095]
After transmitting a cyclic trigger packet (when there is no transmission request for its own cyclic data packet) or after transmitting its own cyclic data (when there is a transmission request for its own cyclic data bucket), A cyclic trigger packet transmission timer activation process (step 504) is executed, and thereafter, each time the cyclic trigger packet transmission timer expires, a series of processes (steps 502, 503, and 504) are repeatedly executed. As a result, the cyclic trigger packet is transmitted from the communication node Node1 assigned to the management station to all other communication nodes NodeZ to NodeN on the serial bus at a constant cycle. Since this cyclic trigger packet is transmitted as an isochronous communication packet, according to the IEEE 1394 scheduled transmission specification, a cyclic trigger packet transmission opportunity can always be obtained once every 125 μsec, thereby improving the periodicity of cyclic data communication. Can be satisfied. In addition, since the transmission of the local data packet is transmitted as an asynchronous communication packet, a maximum data transmission capacity of, for example, 62 μsec can be secured per transmission.
[0096]
On the other hand, as shown in the flowchart of FIG. 6, the other communication nodes Node2 to NodeN serving as normal stations are waiting for a cyclic trigger packet to be transmitted as an isochronous communication packet (step 601 NO, 602 NO).
[0097]
In this state, when reception of a cyclic trigger packet is confirmed as an isochronous communication packet (YES in step 601), in response to this, a transmission process of the local station cyclic data bucket is executed (step 603). As described above, since the transmission of the local data cyclic data packet is transmitted as an asynchronous communication packet, it is possible to secure a data transmission capacity for a maximum of 62 μsec. More specifically, each normal station issues a transmission request for an asynchronous communication packet. Then, the transmission right is given to one of the normal stations that issued the transmission request by the system-defined arbitration acting. In the normal station to which the transmission right is granted, the local station cyclic data transmission process (step 603) is executed, and the local station cyclic data packet is addressed to a predetermined destination as an asynchronous communication packet on the serial bus Bus. Will be sent. When the transmission of the cyclic data packet as an asynchronous communication bucket is completed in one normal station, a transmission request is subsequently issued again from all the remaining normal stations, and arbitration acts to A transmission right is granted to one, and in response to this, a cyclic data packet transmission process is executed. Thereafter, the above operation is repeated until there is no normal station that issues a transmission request (description of FIG. 3). (See figure).
[0098]
On the other hand, the normal station that has completed the transmission processing of its own cyclic data packet starts the cyclic trigger packet waiting timer (step 604). This timer is used for determining that the transmission of the cyclic trigger packet is interrupted due to some cause (communication error or the like).
[0099]
Thereafter, the normal station side waits for the cyclic trigger packet reception while monitoring the timeout of the cyclic trigger packet reception waiting timer (NO in step 602).
[0100]
Then, each time the reception of the cyclic trigger packet is confirmed (step 601 YES), the local station cyclic data transmission process (step 603) and the cyclic trigger packet reception waiting timer activation process (step 604) described above are sequentially performed. Execute. On the other hand, when the timeout of the cyclic trigger packet reception waiting timer is confirmed (step 602 YES), a known management station redetermination process (step 605) is executed. As a result, when an error occurs during some communication and the reception waiting timer for the cyclic trigger packet times out (YES in step 602), the management station redetermination process (step 605) is executed to redetermine the management station. The bus is initialized and the operations described above are repeatedly executed.
[0101]
FIG. 7 shows a time chart showing the transmission timing of cyclic data when the processing shown in the flowcharts of FIGS. 5 and 6 is executed.
[0102]
As shown in the figure, when a cyclic communication cycle is started, a cyclic trigger packet is first transmitted as an isochronous packet from the management station. Then, each normal station sends an asynchronous packet transmission request to the management station side. A known arbitration is executed in response to a transmission request to the management station, and a transmission right is given to one of the plurality of normal stations. The normal station to which the transmission right is given sends out its own cyclic data on the bus as an asynchronous packet. When transmission of cyclic data by one normal station is completed, arbitration is executed one after another, and transmission of cyclic data of the next normal station is repeated.
[0103]
In this time chart, the data from the normal station sent out on the bus in this way is written as “Node A cyclic message”, “Node B cyclic message”,... “Node n cyclic message”. Yes. When the last normal station sends out the cyclic data in this way, there is a waiting time until the next cyclic trigger packet is sent from the management station. The management station transmits a trigger packet for the next trigger packet after a certain period from the reception of the last cyclic data packet.
[0104]
In this way, the management station periodically transmits a trigger packet. When the normal station receives the trigger packet, it transmits a data packet for its own station. Each station receives data packets transmitted by other stations. There are several possible timings for transmitting the trigger packet, such as a preset interval, an interval corresponding to the total data packet amount, and after data packet transmission of all nodes is completed. The time chart of FIG. 7 is an example in which the next trigger packet is transmitted after waiting for a certain time after all nodes transmit the data packet.
[0105]
Cyclic data transfer starts transmission of own station data of each station triggered by reception of a cyclic trigger packet. The cyclic trigger packet is transmitted as an isochronous packet. Each station transmits one cyclic data by receiving one cyclic trigger packet. The management station transmits the cyclic trigger packet.
[0106]
The size of data to be transmitted can be a maximum of 512 bytes per packet according to the IEEE 1394 specification. When the packet requested to be transmitted is larger than 512 bytes, division / assembly is performed in accordance with the IEEE 1394 specification. The divided packets may be transmitted over a plurality of communication cycles, or may be transmitted as continuous packets in one communication cycle.
[0107]
In the example shown in the time chart of FIG. 7, when a packet requested to be transmitted is larger than 512 bytes, a portion exceeding 512 bytes of data to be transmitted is sent to the next cyclic communication cycle.
[0108]
On the other hand, in the example shown in the time chart of FIG. 8, when a packet requested to be transmitted is larger than 512 bytes, the packet to be transmitted is divided into a plurality of fragments (fragments 1 to 3). It is divided and transmitted continuously with a gap in the same cyclic communication cycle. That is, following the cyclic message of node A, three cyclic messages related to node B are continuously transmitted across a gap. Needless to say, these cyclic messages are all transmitted as asynchronous communication packets.
[0109]
The transmission timing of each communication node in the cyclic communication cycle described above is collectively shown in the time chart of FIG.
[0110]
As shown in the figure, in this example, a cyclic communication cycle is constituted by three isochronous cycles (first cycle, second cycle, and third cycle). The start of each isochronous cycle is indicated by a cycle start packet.
[0111]
In the first cycle of the isochronous cycle, a trigger packet is transmitted following the cycle start packet. This trigger packet is transmitted as an isochronous packet. Subsequent to the transmission of the trigger packet, the data packets of the nodes 2, 3 and 4 are sequentially transmitted. These data packets are transmitted by asynchronous communication packets. When the transmission of the node 4 is completed, each normal station waits until the second cycle arrives.
[0112]
In the second cycle, following the transmission of the cycle start packet, the data packet transmission of the node 5 and the node 6 is executed in order. When the transmission of the data packet of the node 6 is completed, each normal station waits until the third cycle arrives.
[0113]
When the third cycle arrives, the cycle start packet arrives, but after that, the whole period waits until the fourth cycle starts.
[0114]
By repeating the above operations, a cyclic communication cycle is realized over three isochronous cycles, and each node has a punctuality defined by the isochronous cycle in a state where a sufficient data transmission capacity is secured. Data transfer can be performed at high speed with each other while being satisfied.
[0115]
Needless to say, while any one of the nodes 1 to 6 is transmitting, the other nodes receive the transmitted data.
[0116]
Thus, according to the cyclic data communication system of the present invention, the trigger packet indicating the start of the cyclic communication cycle is transmitted as an isochronous packet with guaranteed punctuality, while the target transmission data is Asynchronous communication packets are guaranteed with a maximum of 512 bytes per transmission, so IEEE 1394, a widely used general-purpose bus, is adopted, but any cycle length is not limited by its inherent cycle of 125 μsec. Can be realized.
[0117]
In particular, as for the timing of transmitting the trigger packet, various timings such as a preset interval, an interval according to the total data packet amount, and after data packet transmission of all nodes can be freely determined. The degree of design freedom is also improved.
[0118]
Next, FIG. 10 shows a configuration diagram of a PLC system having a data link function to which the present invention is applied. In this example, four programmable logic controllers (PLC1 to PLC4) are connected by an open standard serial bus BUS. As such a serial bus BUS, IEEE1394 or the like can be adopted.
[0119]
Each programmable logic controller PLC1 to PLC4 is provided with four storage areas (PLC1 area, PLC2 area, PLC3 area, PLC4 area). In these storage areas, I / O data relating to the corresponding PLC is stored. That is, in this system, I / O data and the like in all the PLCs are shared with each other.
[0120]
More specifically, PLC1 broadcasts its own station area A11 and receives area data of PLC2-4. Similarly, PLCs 2 to 4 simultaneously broadcast their own station areas and receive other station areas. Thereby, PLC1-PLC4 can share the same data.
[0121]
As is well known, in a PLC, an input / output update process and an instruction execution process are executed, and a system service process is executed every time a certain period comes. In this system service process, Execute data transfer processing.
[0122]
In this embodiment, the cyclic data communication system of the present invention described above is adopted for the data transfer processing for the data link.
[0123]
In other words, the IEEE 1394 bus Bus that connects four PLCs (PLC1 to PLC4) to each other is sequentially connected to each communication node while guaranteeing transmission every isochronous communication cycle for all PLCs that have issued transmission requests. For the isochronous communication phase in which the arbitration function is activated to give a transmission opportunity, and the PLC that issued the transmission request, the maximum value of the transmission data amount is guaranteed in the remaining period after the end of the isochronous communication phase in the isochronous communication cycle. However, an asynchronous communication phase having an arbitration function for sequentially giving each communication node a transmission opportunity is provided.
[0124]
At least one of the plurality of PLCs is assigned to the management station, and the other PLC is assigned to the normal station.
[0125]
The PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase.
[0126]
On the other hand, in response to detecting a cyclic trigger packet transmitted from the control station PLC in the isochronous communication phase, the PLC assigned to the normal station issues a transmission request in the asynchronous communication phase to transmit a transmission opportunity. By transmitting the target data, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the PLC which is another station is received.
[0127]
As a result, the cyclic trigger packet transmission cycle is used as a data communication cycle, and cyclic data communication is performed between the PLCs while using the asynchronous communication phase so that control data such as I / O data is linked to each other. I have to.
[0128]
Next, a configuration diagram of a PLC remote I / O system having a data link function to which the present invention is applied is shown in FIG.
[0129]
In this example, one PLC functioning as a master station and four input / output devices (ID1, OD1, ID2, OD2) functioning as slave stations are connected by an IEEE 1394 bus Bus.
[0130]
This IEEE 1394 bus has an isochronous communication in which an arbitration function for sequentially giving a transmission opportunity to each communication node is ensured while guaranteeing transmission every isochronous communication cycle to all communication nodes that have issued transmission requests. For the communication node that issued the phase and the transmission request, in the remaining period after the end of the isochronous communication phase in the isochronous communication cycle, a transmission opportunity is sequentially provided to each communication node while guaranteeing the maximum value of the transmission data amount And an asynchronous communication phase having an arbitration function for giving.
[0131]
The PLC is assigned to the management station, and the input / output devices (ID1, OD1, ID2, OD2) are assigned to the normal station.
[0132]
In the isochronous communication phase, the PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle by issuing a transmission request and obtaining a transmission opportunity.
[0133]
On the other hand, the input / output device assigned to the normal station issues a transmission request in the asynchronous communication phase in response to detecting the cyclic trigger packet sent from the control station PLC in the isochronous communication phase. By obtaining the transmission opportunity, the target data is transmitted, or when the transmission opportunity is not obtained, the data transmitted from the PLC as the management station is received.
[0134]
As a result, cyclic communication is performed while using the asynchronous communication phase between the PLC and each input / output device (ID1, OD1, ID2, OD2) using the cyclic trigger packet transmission cycle as a data communication cycle. Thus, I / O data is linked between them.
[0135]
Finally, FIG. 12 shows a configuration diagram of a PLC system having a data link function to which the present invention is applied and having a remote I / O system.
[0136]
This system includes four programmable logic controllers PLC1 to PLC4 and four input / output devices (ID1, OD1, ID2, OD2).
[0137]
The four PLCs and the four input / output devices are connected by an open standard serial bus. As such a bus, IEEE1394 or the like can be adopted.
[0138]
PLC1 to PLC4 realize the data link function as described with reference to FIG. On the other hand, the data link function described with reference to FIG. 11 is realized between the PLC 1 and the input / output devices (ID1, OD1, ID2, OD2).
[0139]
Therefore, according to this system, while realizing the data link function among the four programmable logic controllers PLC1 to PLC4, one PLC functioning as a master and four remotely installed input / output devices ( By realizing a data link with ID1, OD1, ID2, OD2), it is possible to realize an extremely sophisticated control system while maintaining high responsiveness.
[0140]
In each of the embodiments described above, IEEE 1394 is cited as the serial bus to which the present invention is applied. However, the application of the present invention is not limited to this. In short, the cyclic data communication system of the present invention is designed to provide each communication node with a transmission opportunity sequentially while guaranteeing transmission every time for a specific communication cycle to all communication nodes that have issued transmission requests. For each communication node while guaranteeing the maximum value of the transmission data amount for the remaining period excluding the scheduled communication phase in the unique communication cycle for the scheduled communication phase in which the arbitration function operates and the communication node that issued the transmission request In contrast, the present invention can be widely applied to a standardized serial bus provided with an asynchronous communication phase in which an arbitration function for sequentially providing transmission opportunities is activated.
[0141]
【The invention's effect】
As is apparent from the above description, according to the present invention, for example, as in the IEEE 1394 bus, open standardization having both a regular communication phase (corresponding to an isochronous communication phase) and an asynchronous communication phase (corresponding to an asynchronous communication phase). On the premise of the serial bus specification, cyclic data transfer having punctuality can be realized while guaranteeing the maximum transmission data amount of each communication node.
[Brief description of the drawings]
FIG. 1 is a time chart showing a standard transmission procedure of an IEEE 1394 bus.
FIG. 2 is a time chart showing data communication using all isochronous cycles as an isochronous phase.
FIG. 3 is an explanatory diagram showing a relationship between a serial bus and each communication node.
FIG. 4 is a block diagram schematically showing a hardware configuration of each communication node.
FIG. 5 is a flowchart showing processing on the management station side.
FIG. 6 is a flowchart showing processing on the normal station side.
FIG. 7 is a time chart showing the transmission timing of cyclic data.
FIG. 8 is an explanatory diagram illustrating an example of transmission timing of divided data.
FIG. 9 is a time chart showing the transmission timing of each communication node in a cyclic communication cycle.
FIG. 10 is a configuration diagram of a PLC system having a data link function.
FIG. 11 is a configuration diagram of a PLC remote I / O system having a data link function;
FIG. 12 is a configuration diagram of a PLC system having a data link function and having a remote I / O system.
[Explanation of symbols]
Bus serial bus
400 Circuit device
401 Communication controller
402 CPU
403 ROM
404 RAM
405 Send / Receive buffer
406 Isochronous Resource Register
A11-A44 PLC I / O data storage area
ID1, ID2 input device
OD1, OD2 output device

Claims (8)

Multiple communication nodes are connected by a serial bus with a unique communication cycle,
The serial bus
For all communication nodes that issued a transmission request, the sequentially transmission opportunity to each communication node while ensuring transmission every respect unique communication cycle, the phase when the communication node has run out for emitting transmission request A scheduled communication phase in which the arbitration function to be terminated operates,
In the remaining period following the scheduled communication phase within a unique communication cycle, an arbitration function is activated to sequentially give a transmission opportunity to each communication node that has issued a transmission request while guaranteeing the maximum value of the transmission data amount. An asynchronous communication phase,
At least one of the plurality of communication nodes is assigned to the management station, and the other communication node is assigned to the normal station.
The communication node assigned to the management station periodically transmits a cyclic trigger code indicating the start of a communication cycle in the regular communication phase.
The communication node assigned to the normal station issues a transmission request in the asynchronous communication phase in response to detecting the cyclic trigger code transmitted from the communication node assigned to the management station in the regular communication phase. By obtaining the transmission opportunity, transmit the target data, or when not receiving the transmission opportunity, receive the data transmitted from the communication node which is another station,
As a result, cyclic data that enables cyclic data communication across multiple unique communication cycles while using the asynchronous communication phase between communication nodes with the cyclic trigger code transmission cycle as the data communication cycle Communications system. Multiple communication nodes are connected by the IEEE 1394 bus,
The IEEE 1394 bus has
For all communication nodes that issued a transmission request, sequentially provide a transmission opportunity to each communication node while ensuring transmission each time for isochronous communication cycle, the phase when the communication node has run out for emitting transmission request An isochronous communication phase in which the arbitration function is terminated ;
Sequential transmission to each communication node that issued a transmission request while guaranteeing the maximum amount of transmission data for the remaining period after completion of the isochronous communication phase in the isochronous cycle to the communication node that issued the transmission request And an asynchronous communication phase in which an arbitration function is activated to give an opportunity,
At least one of the plurality of communication nodes is assigned to the management station, and the other communication node is assigned to the normal station.
The communication node assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase,
The communication node assigned to the normal station issues a transmission request in the asynchronous communication phase in response to detecting a cyclic trigger packet transmitted from the communication node assigned to the management station in the isochronous communication phase. By obtaining the transmission opportunity, transmit the target data, or when not receiving the transmission opportunity, receive the data transmitted from the communication node which is another station,
As a result, cyclic data communication that enables cyclic data communication across multiple isochronous communication cycles while using the asynchronous communication phase between communication nodes with the cyclic trigger packet transmission cycle as the data communication cycle system.  The cyclic data communication system according to claim 1 or 2, wherein the transmission timing of the cyclic trigger packet is obtained by calculation based on a total amount of transmission data per scheduled communication cycle.  The cyclic data communication system according to claim 1 or 2, wherein the transmission timing of the cyclic trigger packet is determined by interruption of transmission data in the asynchronous phase. Multiple PLCs are connected by the IEEE1394 bus,
The IEEE 1394 bus has
For all communication nodes that issued a transmission request, sequentially provide a transmission opportunity to each communication node while ensuring transmission each time for isochronous communication cycle, the phase when the communication node has run out for emitting transmission request An isochronous communication phase in which the arbitration function is terminated ;
For each communication node that has issued a transmission request while guaranteeing the maximum value of the amount of transmission data in the remaining period after the end of the isochronous communication phase in the isochronous communication cycle for the communication node that has issued the transmission request. And an asynchronous communication phase having an arbitration function for giving a transmission opportunity,
At least one of the plurality of PLCs is assigned to the management station, and the other PLC is assigned to the normal station.
The PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase,
In response to detecting a cyclic trigger packet transmitted from the control station PLC in the isochronous communication phase, the PLC assigned to the normal station issues a transmission request and obtains a transmission opportunity in the asynchronous communication phase. By receiving the data transmitted from the PLC, which is another station, when the target data is transmitted or the transmission opportunity is not obtained,
Thus, a PLC system in which control data is linked to each other by cyclically performing data communication between PLCs using the asynchronous communication phase using the transmission cycle of the cyclic trigger packet as a data communication cycle. One PLC and multiple input / output devices are connected by an IEEE1394 bus.
The IEEE 1394 bus has
For all communication nodes that issued a transmission request, sequentially provide a transmission opportunity to each communication node while ensuring transmission each time for isochronous communication cycle, the phase when the communication node has run out for emitting transmission request An isochronous communication phase in which the arbitration function is terminated ;
For each communication node that has issued a transmission request while guaranteeing the maximum value of the amount of transmission data in the remaining period after the end of the isochronous communication phase in the isochronous communication cycle for the communication node that has issued the transmission request. And an asynchronous communication phase having an arbitration function for giving a transmission opportunity,
The PLC is assigned to the management station, and the input / output device is assigned to the normal station.
The PLC assigned to the management station periodically transmits a cyclic trigger packet indicating the start of a communication cycle in the isochronous communication phase.
In response to detecting the cyclic trigger packet transmitted from the control station PLC in the isochronous communication phase, the input / output device assigned to the normal station issues a transmission request in the asynchronous communication phase and transmits a transmission opportunity. To receive the data transmitted from the PLC, which is the management station, when the target data is transmitted, or when the transmission opportunity is not obtained,
As a result, the cyclic trigger packet transmission cycle is used as a data communication cycle, and cyclic data communication is performed between the PLC and each input / output device using the asynchronous communication phase. PLC remote I / O system that links data.  The system according to claim 5 or 6, wherein the transmission timing of the cyclic trigger packet is obtained by calculation based on a total amount of transmission data per scheduled communication cycle.  The system according to claim 5 or 6, wherein the transmission timing of the cyclic trigger packet is determined by interruption of transmission data in the asynchronous communication phase.

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