COMMUNICATION SYSTEM, COMMUNICATION CONTROL METHOD, AND COMMUNICATION CONTROL PROGRAM

Abstract

To provide a configuration capable of generating information about failures that may occur in a network even when a function for monitoring the occurrence of errors occurring in frames, which is implemented in a slave device, is not sufficient.SOLUTION: A communication system includes: a communication unit connected to one or more slave devices via a network; acquisition means for acquiring the number of error occurrences detected by first error monitoring means from at least one of the one or more slave devices; and generation means for generating information about failures that may occur in the network based on the acquired number of error occurrences. The acquisition means acquires the number of error occurrences at a cycle corresponding to time when the first error monitoring means can reach the maximum value of the number of error occurrences that can be stored.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a communication system including a network, a communication control method executed in a communication device, and a communication control program for implementing the communication control method. [Background technology]

[0002] For example, in a network conforming to EtherCAT (registered trademark), a frame transmitted by a master device travels through all slave devices before returning to the master device.

[0003] For example, Japanese Patent Laid-Open Publication No. 2011-119999 (Patent Document 1) discloses a technique for reducing the processing time required when a master device receives data from a slave device in a system including a master device and multiple slave devices.

[0004] Usually, when a part of the path along which a frame circulates is cut or the like, the frame cannot be transmitted beyond the cut point.

[0005] Regarding such a communication method, Japanese Patent Application Laid-Open Publication No. 2017-153050 (Patent Document 2) discloses a technique for monitoring the occurrence of a communication error in connectionless communication, regardless of whether the system is in operation or not. In addition, although it is not a technique related to a network in which frames circulate, International Publication No. 2013 / 014793 (Patent Document 3) discloses a communication device that can easily identify the location of a bus error.

[0006] In addition, JP 2019-101970 A (Patent Document 4) discloses a technology that makes it easier to identify the cause of an abnormal event that occurs in a control device that is network-connected to one or more devices. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-119999 A [Patent Document 2] JP 2017-153050 A [Patent Document 3] International Publication No. 2013 / 014793 [Patent Document 4] JP 2019-101970 A Summary of the Invention [Problem to be solved by the invention]

[0008] Japanese Patent Laid-Open Publication No. 2017-153050 (Patent Document 2) discloses a configuration for collecting information indicating the number of occurrences (error count) from a slave device, but the error monitoring function of the slave device is not as extensive as that of the slave device, and therefore the capacity for storing information regarding errors is often limited.

[0009] An object of one aspect of the present invention is to provide a configuration that can generate information regarding faults that may occur in a network, even if the slave device does not have a comprehensive function for monitoring the occurrence of errors in frames. [Means for solving the problem]

[0010] A communication system according to an embodiment includes a communication unit connected to one or more slave devices via a network. The network is configured such that a frame transmitted from the communication unit returns to the communication unit after making a round trip around the one or more slave devices, and each of the one or more slave devices includes a first error monitoring means for monitoring the occurrence of an error in a received frame. The communication system includes an acquisition means for acquiring a number of errors detected by the first error monitoring means from at least one of the one or more slave devices, and a generation means for generating information on a fault that may occur in the network based on the acquired number of errors. The acquisition means acquires the number of errors at a period corresponding to the time that the first error monitoring means may reach a maximum value for the number of errors that can be stored.

[0011] According to this configuration, the acquisition means acquires the number of error occurrences at a period corresponding to the time when the first error monitoring means of the slave device may reach the maximum number of error occurrences that can be stored, so that the number of error occurrences can be appropriately acquired from the slave device, and thus information regarding faults that may occur in the network can be appropriately generated.

[0012] The acquisition means may be configured to reset the number of errors detected by the first error monitoring means after acquiring the number of errors detected by the first error monitoring means. This configuration makes it possible to prevent the number of errors held by the first error monitoring means of the slave device from overflowing.

[0013] The communication unit may include a second error monitoring means for monitoring the occurrence of errors occurring in received frames. The acquisition means may start acquiring the number of errors when the number of errors detected by the second error monitoring means satisfies a predetermined condition. With this configuration, the number of errors is acquired from the slave device only when there is a high possibility that some kind of failure has occurred in the network, so that network bandwidth is not unnecessarily consumed.

[0014] The communication system may further include a means for identifying a location in the network where a fault has occurred based on the acquired number of errors. With this configuration, even a user with little expert knowledge can quickly determine at a glance where in the network a fault has occurred.

[0015] The generating means may calculate a failure rate of the target slave from a ratio of the number of errors occurring in the target slave to the number of frames transmitted from the communication unit, and may determine the severity based on the calculated failure rate. With this configuration, the user can easily understand the severity of a fault that has occurred in the network, and objectively grasp the level of urgency with which a measure must be taken.

[0016] The communication system may further include a notification unit that notifies a user of information related to the failure. With this configuration, it is possible to provide a user with information that is useful for determining how to deal with a failure that may occur in the network and when to take such action.

[0017] The information about the fault may include information used for predictive maintenance of possible faults in the network, so that necessary measures can be taken before a permanent fault occurs in the network.

[0018] According to another embodiment, there is provided a communication control method executed in a communication device connected to one or more slave devices via a network. The network is configured such that a frame transmitted from the communication device returns to the communication device after circulating around the one or more slave devices. Each of the one or more slave devices includes an error monitoring means for monitoring occurrence of an error occurring in a received frame. The communication control method includes a step of acquiring the number of errors detected by the error monitoring means from at least one of the one or more slave devices, and a step of generating information on a fault that may occur in the network based on the acquired number of errors. The acquiring step includes a step of acquiring the number of errors at a period corresponding to the time when the error monitoring means may reach a maximum value of the number of errors that can be stored.

[0019] According to yet another embodiment, there is provided a communication control program executed by a computer connected to one or more slave devices via a network. The network is configured such that a frame transmitted from the computer returns to the computer after circulating through the one or more slave devices. Each of the one or more slave devices includes an error monitoring means for monitoring occurrence of an error occurring in a received frame. The communication control program causes the computer to execute a step of acquiring the number of errors detected by the error monitoring means from at least one of the one or more slave devices, and a step of generating information on a fault that may occur in the network based on the acquired number of errors. The acquiring step includes a step of acquiring the number of errors at a period corresponding to the time when the error monitoring means can reach the maximum number of errors that can be stored. Effect of the Invention

[0020] According to one embodiment, even if the functionality implemented in a slave device for monitoring the occurrence of errors in frames is not extensive, a configuration can be realized that is capable of generating information regarding faults that may occur in the network. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing an example of a network configuration of a communication system according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram showing an example of a functional configuration of a communication system according to the present embodiment. [Diagram 3] FIG. 2 is a schematic diagram showing an example of a hardware configuration of a master in the communication system according to the present embodiment. [Figure 4] FIG. 2 is a schematic diagram showing an example of a hardware configuration of a slave in the communication system according to the present embodiment. [Diagram 5] 1 is a diagram for explaining an example of frame transmission and a failure that may occur in a communication system according to the present embodiment. [Figure 6]11A and 11B are diagrams illustrating an example of an error detection result when a failure occurs in the communication system according to the present embodiment. [Figure 7] 10 is a flowchart showing a process procedure relating to fault monitoring in the communication system according to the present embodiment. [Figure 8] FIG. 1 illustrates an example of a case where a failure occurs in a communication system according to the present embodiment. [Figure 9] FIG. 11 is a diagram showing an example of a processing procedure for identifying a location where a failure has occurred in the communication system according to the present embodiment. [Figure 10] 11 is a diagram for illustrating a process for acquiring the number of errors that have occurred in the communication system according to the present embodiment. FIG. [Figure 11] 4 is a schematic diagram showing an example of a user interface screen provided by the communication system according to the present embodiment. FIG. [Figure 12] 13 is a schematic diagram showing another example of a user interface screen provided by the communication system according to the present embodiment. FIG. [Figure 13] 13 is a schematic diagram showing another example of a user interface screen provided by the communication system according to the present embodiment. FIG. [Figure 14] FIG. 13 is a schematic diagram showing yet another example of a user interface screen provided by the communication system according to the present embodiment. [Figure 15] FIG. 13 is a schematic diagram showing yet another example of a user interface screen provided by the communication system according to the present embodiment. [Figure 16] FIG. 13 is a schematic diagram showing yet another example of a user interface screen provided by the communication system according to the present embodiment. [Figure 17] FIG. 13 is a schematic diagram showing yet another example of a user interface screen provided by the communication system according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0023] <A. Application Example> First, an example of a scenario to which the present invention is applied will be described.

[0024] FIG. 1 is a schematic diagram showing a network configuration example of a communication system 1 according to the present embodiment. Referring to FIG. 1, the communication system 1 includes a master device 100 that is a communication master and slave devices 200-1 to 200-4 that are communication slaves. In the following description, the "master device" will also be abbreviated as "master", and the "slave device" will also be abbreviated as "slave".

[0025] In the following description, as an example of a communication device, a PLC (programmable logic controller) that executes arbitrary control operations is assumed for description, but the present invention is applicable not only to a PLC but also to any device that can function as a master.

[0026] The master 100 and the slaves 200-1 to 200-4 (hereinafter, may also be collectively referred to as "slave 200") are sequentially connected (daisy chain connection) by links 20-1 to 20-4 (hereinafter, may also be collectively referred to as "link 20") to form a network as a whole. The frame sent from the master 100 returns to the master 100 after making a round trip through the path passing through the slaves 200 connected to the network. In this way, the network is configured such that the frame transmitted from the master 100 (the communication unit of the master 100) returns to the master 100 (the communication unit of the master 100) after making a round trip through one or more slaves 200.

[0027] The master 100 periodically transmits a frame and manages the transmission of the frame. As a typical network, a network conforming to EtherCAT is assumed.

[0028] The master 100 may be further connected to a support device 300 and a server device 400 via a higher level network 2 .

[0029] Fig. 2 is a schematic diagram showing an example of a functional configuration of communication system 1 according to the present embodiment. Referring to Fig. 2, master 100 functions as an EtherCAT communication master, and slave 200 functions as an EtherCAT communication slave. Master 100 includes, as its functional configuration, an acquisition module 150, a generation module 160, an identification module 170, and a notification module 180.

[0030] Each of the slaves 200 has an error monitoring function 234 that monitors the occurrence of errors occurring in received frames. The error monitoring function 234 can be realized, for example, by using an ESC (EtherCAT Slave Controller). The ESC can monitor abnormal communications, such as the number of received error frames, and count the number of occurrences.

[0031] The number of errors detected by the error monitoring function 234 (hereinafter also referred to as the "error occurrence count") is stored in an error occurrence count storage register 236. The upper limit of the value that can be stored in the error occurrence count storage register 236 is determined according to the number of bits assigned to the error occurrence count storage register 236. For example, if the error occurrence count storage register 236 is provided with 8 bits, the upper limit of the number of error occurrences that can be stored in the error occurrence count storage register 236 is 255.

[0032] The acquisition module 150 of the master 100 acquires the number of errors detected by the error monitoring function 234 from at least one slave 200. More specifically, the acquisition module 150 transmits a read command for reading the number of errors to the target slave 200. In EtherCAT, a command (BRD) for reading the number of errors from all slaves 200 and a command (FPRD) for reading the number of errors from a specific slave 200 are provided. The acquisition module 150 transmits either command to the slave 200 depending on the situation. In addition, the acquisition module 150 transmits a command for resetting the error number storage register 236 to the target slave 200.

[0033] Each of the slaves 200 responds to a command from the acquisition module 150 of the master 100 and transmits the results of the read and reset to the master 100. The results of the read and reset include the number of errors that occurred and a notification that the reset has been completed.

[0034] At this time, the acquisition module 150 acquires the number of error occurrences at a period (acquisition period) according to the time it takes for the error monitoring function 234 to reach the maximum number of error occurrences that can be stored (the upper limit of the error occurrence number storage register 236). By appropriately determining such an acquisition period, it is possible to prevent a situation in which the error occurrence number storage register 236 overflows. The method of determining the acquisition period will be described in detail later.

[0035] The error occurrence count acquired by the acquisition module 150 from one or more slaves 200 is output to the generation module 160 and the identification module 170. The error occurrence count acquired by the acquisition module 150 may be stored not only inside the master 100 but also in the support device 300 and / or the server device 400 (see FIG. 1 for both).

[0036] The generation module 160 of the master 100 generates information about faults that may occur in the network based on the acquired number of error occurrences. Specific examples of information about faults will be described later.

[0037] Based on the obtained number of error occurrences, the specific module 170 of the master 100 identifies the location where a failure has occurred in the network.

[0038] The notification module 180 of the master 100 notifies a user or the like of the information on the failure generated by the generation module 160 and / or the information on the location where a failure has occurred in the network identified by the specific module 170.

[0039] Note that all or part of the generation module 160, the specific module 170, and the notification module 180 may be implemented in the support device 300 and / or the server device 400.

[0040] That is, the support device 300 and / or the server device 400 may generate an interface screen including a graph indicating information, a network configuration, etc., using information such as the number of error occurrences from the master 100. Further, the server device 400 may display on the interface screen the locations where predictive maintenance is required.

[0041] <B. Hardware Configuration Example> Next, a hardware configuration example of the devices included in the communication system 1 according to the present embodiment will be described.

[0042] (b1: Master 100) FIG. 3 is a schematic diagram showing a hardware configuration example of the master 100 of the communication system 1 according to the present embodiment. Referring to FIG. 3, the master 100 is an example of a computer, and as main hardware components, it includes a processor 102, a main memory 104, a storage 110, a local bus controller 112, an upper network interface 120, and a network controller 130. These hardware components are electrically connected via a bus 118.

[0043] The processor 102 corresponds to an arithmetic processing unit that executes control calculations, and is composed of a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc. Specifically, the processor 102 reads out a program stored in the storage 110, expands it in the main memory 104, and executes it to realize control calculations according to a control target and various processes to be described later.

[0044] The main memory 104 is configured with a volatile storage device such as a dynamic random access memory (DRAM) or a static random access memory (SRAM). The storage 110 is configured with a non-volatile storage device such as a solid state drive (SSD) or a hard disk drive (HDD).

[0045] The storage 110 stores a system program 1102 for implementing basic functions, a user program 1104 created according to a control target, and the like. The system program 1102 implements basic functions in the master 100 and can therefore be regarded as at least a part of the communication control program.

[0046] The local bus controller 112 is electrically connected to one or more functional units 114 via an internal bus 116. The functional unit 114 includes a function of exchanging various signals with a control target. The functional unit 114 has one or more functions, for example, a DI (Digital Input) function of receiving a digital signal from the control target, a DO (Digital Output) function of outputting a digital signal to the control target, an AI (Analog Input) function of receiving an analog signal from the control target, and an AO (Analog Output) function of outputting an analog signal to the control target. Furthermore, the functional unit 114 may include a controller that implements special functions such as PID (Proportional Integral Derivative) control and motion control.

[0047] The upper network interface 120 is responsible for communication via the upper network 2 .

[0048] The network controller 130 corresponds to a communication unit connected to one or more slaves 200 via a network. More specifically, the network controller 130 includes a communication control circuit 132 and a communication circuit 140. The communication circuit 140 includes a receiving unit 142 and a transmitting unit 144. The network controller 130 may have a synchronous counter for periodically transmitting and receiving frames.

[0049] The communication control circuit 132 controls the reception of frames by the communication circuit 140 and the transmission of frames from the communication circuit 140. The communication control circuit 132 has an error monitoring function 134 that monitors the occurrence of errors in the communication circuit 140. The error monitoring function 134 monitors the occurrence of errors in frames received by the communication circuit 140.

[0050] The receiving unit 142 receives a frame and outputs the information contained in the frame to the communication control circuit 132. The transmitting unit 144 generates and transmits a frame in accordance with a command from the communication control circuit 132.

[0051] FIG. 3 shows an example of a configuration in which the processor 102 executes a program to provide necessary functions, but some or all of these provided functions may be implemented using a dedicated hardware circuit (e.g., an Application Specific Integrated Circuit (ASIC) or a Field-Programmable Gate Array (FPGA)). Alternatively, the main part of the master 100 may be realized using hardware that conforms to a general-purpose architecture (e.g., an industrial PC based on a general-purpose PC). In this case, a virtualization technology may be used to run multiple OSs (Operating Systems) with different uses in parallel, and necessary applications may be executed on each OS.

[0052] Furthermore, the master 100 may be configured to incorporate the functions of a display device, a support device, and the like.

[0053] (b2: Slave 200) Fig. 4 is a schematic diagram showing an example of a hardware configuration of slave 200 in communication system 1 according to the present embodiment. Referring to Fig. 4, slave 200 includes, as main hardware components, a control circuit 206, a functional module 220, and a network controller 230.

[0054] The control circuit 206 is an arithmetic processing unit that proactively executes processing in the slave 200. The control circuit 206 typically includes a processor 202, a main memory 204, and a storage 210. The processor 202 is configured with a CPU, a GPU, or the like. The main memory 204 is configured with a volatile storage device, such as a DRAM or an SRAM, or the like. The storage 210 is configured with a non-volatile storage device, such as an SSD, or the like. Note that a ROM (Read Only Memory) may be adopted as the storage 210.

[0055] The control circuit 206 may be implemented using a dedicated hardware circuit (eg, ASIC or FPGA).

[0056] The functional module 220, like the functional unit 114 shown in FIG. 3, is responsible for processing such as exchanging various signals with the controlled object.

[0057] The network controller 230 includes a communication control circuit 232, a first port 240, and a second port 250. The network controller 230 may have a synchronous counter for periodically transmitting and receiving frames.

[0058] The communication control circuit 232 controls the reception of frames by the first port 240 and the second port 250 and the transmission of frames from the first port 240 and the second port 250. The communication control circuit 232 has an error monitoring function 234 that monitors the occurrence of errors in the first port 240 and the second port 250.

[0059] The first port 240 includes a receiver 242 and a transmitter 244. Similarly, the second port 250 includes a receiver 252 and a transmitter 254.

[0060] The receiving units 242 and 252 receive frames and output information contained in the frames to the communication control circuit 232. The transmitting units 244 and 254 generate and transmit frames according to instructions from the communication control circuit 232.

[0061] For convenience of explanation, an example configuration having two ports is shown, but a configuration having more ports may be adopted.

[0062] (b3: Support device 300) The support device 300 provides functions for developing and debugging a user program 1104 executed by the PLC, which is the master 100. The support device 300 also provides a user interface for providing various information as described later.

[0063] The support device 300 is typically realized by a general-purpose personal computer, and therefore a detailed description of the hardware configuration will not be given.

[0064] (b4: server device 400) The server device 400 acquires information from the PLC which is the master 100, and responds with the acquired information in response to an external request. The server device 400 is also typically realized by a general-purpose personal computer, so a detailed description of the hardware configuration will not be given.

[0065] The server device 400 can implement arbitrary processing and functions. For example, the server device 400 may have a database 410 that stores information from the master 100 and a web server 420 that provides arbitrary web pages.

[0066] <C. Frame Transmission and Failure> Next, frame transmission and possible failures in the communication system 1 according to the present embodiment will be described.

[0067] FIG. 5 is a diagram for explaining an example of frame transmission and possible failures in the communication system 1 according to the present embodiment. Referring to FIG. 5(A), the frame transmitted from the master 100 is sequentially transferred to the slaves 200-1 to 200-4 via the links 20-1 to 20-4. In the example of FIG. 5(A), the frame received by 200-4 at the end is folded back and sequentially transferred toward the master 100. Finally, the frame reaches the master 100.

[0068] FIG. 5(B) shows a state when some failure occurs in the link 20-2 between the slave 200-1 and the slave 200-2.

[0069] In this specification, "failure" is a concept that includes any event that adversely affects frame transmission. "Failure" includes, for example, those caused by external noise that inhibits frame transmission, those caused by component deterioration, those caused by cable disconnection or breakage, and the like.

[0070] In this case, the frame may not be able to be transmitted through the link 20-2, or data damage or loss included in the frame may occur by passing through the link 20-2.

[0071] Each of the master 100 and the slave 200 monitors for the occurrence of an error. Errors may include (1) a frame reception timeout in which a frame cannot be received within a predetermined time, and (2) a received frame that is invalid due to corruption or loss of data contained in the received frame (occurrence of an error frame). For example, a frame includes an error detection code such as a CRC (Cyclic Redundancy Check), and by calculating the check bits from the data contained in the received frame, it can be determined whether or not the received frame includes any errors (i.e., whether or not it is an error frame).

[0072] 5B, the number of errors that occur in frames transmitted from slave 200-1 to slave 200-2 and in frames transmitted from slave 200-2 to slave 200-1 may increase. That is, the number of errors detected in the receiving units of slave 200-1 and slave 200-2 increases.

[0073] In this way, if any kind of failure occurs in the path along which the frame circulates, the frame cannot be transmitted properly, and the control calculations by the master 100, the PLC, will not be executed properly, which may result in the production facilities and manufacturing equipment stopping.

[0074] 6 is a diagram showing an example of an error detection result when a failure occurs in communication system 1 according to the present embodiment. The error detection result shown in FIG. 6 is usually provided by master 100 by acquiring it from each of slaves 200.

[0075] Referring to FIG. 6, for the fault shown in FIG. 5(B), an error will be detected at the second port of slave 200-1 corresponding to node address "001" and the first port of slave 200-2 corresponding to node address "002."

[0076] Generally, when identifying the location where a failure has occurred from the error detection results as shown in FIG. 6, it is necessary to check the path through which the frame is transmitted and identify the location where the number of errors has increased. For the identified location, measures such as replacing the communication cable or removing the noise source are taken.

[0077] To identify the location where such a failure has occurred, a certain degree of expertise is required. The communication system 1 according to the present embodiment provides a mechanism for early detection of failures that may occur in the network and for facilitating the identification of the location where the failure has occurred.

[0078] <D. Processing Procedure> Next, the processing procedure related to failure monitoring in the communication system 1 according to the present embodiment will be described.

[0079] FIG. 7 is a flowchart showing the processing procedure related to failure monitoring in the communication system 1 according to the present embodiment. Each step shown in FIG. 7 is typically realized by the processor 102 of the master 100 executing a system program 1102 which is an example of a communication program.

[0080] In the communication control method shown in FIG. 7, the master 100 acquires the statistical information of the errors detected by the communication control circuit 132 (error monitoring function 134) of the network controller 130 (step S1). Then, the master 100 determines whether or not the number of error occurrences is increasing based on the acquired statistical information of the errors (step S2).

[0081] If it is determined that the number of error occurrences is not increasing (NO in step S2), the processing below step S1 is repeated. On the other hand, if it is determined that the number of error occurrences is increasing (YES in step S2), the processing below step S3 is executed. That is, the master 100 starts acquiring the number of error occurrences below step S3 when the number of error occurrences detected by the error monitoring function 134 satisfies a predetermined condition.

[0082] First, the master 100 acquires the number of error occurrences from one or more slaves 200 connected to the network (step S3). That is, the master 100 (acquisition module 150 shown in FIG. 2) acquires the number of error occurrences detected by the error monitoring function 234 from at least one of the one or more slaves 200.

[0083] Then, the master 100 identifies the location where some failure has occurred (step S4). That is, the master 100 (identification module 170 shown in FIG. 2) identifies the location in the network where a failure has occurred based on the acquired number of error occurrences.

[0084] Furthermore, the master 100 determines the slaves 200 to be the acquisition targets of the number of error occurrences and generates information regarding the failure (step S5). That is, the master 100 (generation module 160) generates information regarding the possible failures in the network based on the acquired number of error occurrences.

[0085] Also, the master 100 determines the acquisition period of the number of error occurrences (step S6).

[0086] Furthermore, the master 100 executes a process for providing information regarding the failure (step S7). That is, the master 100 (notification module 180 shown in FIG. 2) notifies the user of the information regarding the failure.

[0087] The above-described processing procedures are repeated at a predetermined period or for each predetermined event.

[0088] <E. Judgment of Increase in the Number of Error Occurrences (Steps S1 and S2)> Next, the details of the processing related to steps S1 and S2 of the processing procedure shown in FIG. 7 will be described.

[0089] In step S1, the (1) number of frame reception timeouts and (2) number of error frame occurrences detected by the communication control circuit 132 of the master 100 may be acquired.

[0090] In the determination of whether the number of error occurrences is increasing (step S2), a threshold value may be set for each value, or a threshold value may be set for the sum of two values. Further, the determination may be made based on the absolute value of the acquired number of timeouts and / or the number of occurrences of error frames, or the determination may be made based on the tendency of the value to change (such as the acceleration of increase).

[0091] As shown in FIG. 7, until it is determined that the number of error occurrences is increasing, the process of acquiring information from the slave 200 after step S3 is not executed, so that the use of the network bandwidth due to the information acquisition from the slave 200 can be suppressed. That is, by using the increase in the number of error occurrences as a trigger for information acquisition from the slave 200, the network bandwidth can be efficiently used, and an increase in the communication load occurring in the slave 200 can also be suppressed.

[0092] Note that the processing procedure shown in FIG. 7 may be stopped when the failure occurring in the network reaches a predetermined level or higher. That is, when the failure occurring in the network becomes permanent, the occurrence status of the failure such as the number of error occurrences does not change, so there is little need to continue monitoring periodically. Therefore, the monitoring process may be terminated by notifying the occurrence of the failure. By adopting a mechanism for acquiring information from the slave 200 only in such a situation where such periodic monitoring is necessary, the compression of the network bandwidth and the consumption of processing resources can be suppressed. Note that, according to user settings, the monitoring process may be continued in any situation.

[0093] <F. Acquisition of the Number of Error Occurrences and Identification of the Fault Location (Steps S3 and S4)> Next, the details of the processing according to steps S3 and S4 of the processing procedure shown in FIG. 7 will be described.

[0094] Fig. 8 is a diagram showing an example of a case where a failure occurs in communication system 1 according to the present embodiment. Fig. 8(A) shows, as an example, a case where some failure occurs on a path from slave 200-3 to slave 200-2.

[0095] Fig. 8(B) shows the number of errors detected at each port of each slave 200 in the state shown in Fig. 8(A) in association with the path that the frame circulates. As shown in Fig. 8(B), it can be seen that the number of errors is greater at the second port and onwards of slave 200-2 connected to the section where the failure has occurred, compared to the other slaves 200.

[0096] The location of the failure may be identified after obtaining the number of errors from all slaves 200, or the location of the failure may be identified by sequentially selecting target slaves 200 with reference to route information such as that shown in FIG. 8(B).

[0097] Fig. 9 is a diagram showing an example of a processing procedure for identifying a location where a failure has occurred in communication system 1 according to the present embodiment. Fig. 9 shows an example of identifying a location where a failure has occurred by a binary search method.

[0098] First, as shown in Fig. 9(A), the number of errors is obtained from a node (slave 200) located in the middle of the path that the frame makes a loop. Based on whether the obtained number of errors is relatively high or not, it is determined whether the failure has occurred in the first half or the second half of the path that the frame makes a loop. Then, the number of errors is obtained from a node (slave 200) located in the middle of the determined part.

[0099] In the example shown in FIG. 9(A), since the number of errors occurring at the first port of slave 200-4 is relatively low, it is determined that a fault has occurred in the latter half of the path, and the number of errors occurring is obtained from the node (slave 200) located in the middle of the latter half of the path, as shown in FIG. 9(B).

[0100] By repeating such a procedure, it is possible to identify at which location on the path a failure has occurred.

[0101] Note that not only the binary search method as described above may be used, but also another method may be employed. For example, if it is possible to obtain the number of error occurrences from all slaves 200 connected to the network with a single command transmitted from master 100, then all necessary information may be obtained from all slaves 200 at once using such a command.

[0102] Alternatively, when master 100 individually obtains the necessary information from each of slaves 200, the target slave 200 may be sequentially selected in time so as to obtain information in a divided period. By obtaining information in such a divided period, compression of the network bandwidth can be suppressed.

[0103] <G. Generation of Information Regarding Failure (Step S5)> Next, the details of the process according to step S5 of the process procedure shown in FIG. 7 will be described.

[0104] As information regarding the generated failure, in addition to the information indicating the location where the failure has occurred as described above, the following failure rate and criticality may be calculated.

[0105] In this specification, the "failure rate" indicates the ratio of the number of error occurrences in the target slave 200 with respect to the frames transmitted from master 100. That is, the failure rate can be calculated according to the following formula.

[0106] Failure rate = (Number of error occurrences in the target slave) / (Number of frames transmitted by the master) Master 100 calculates the failure rate for any slave 200 under any conditions. Typically, the failure rate is calculated on the condition that it is determined that the number of error occurrences is increasing. Alternatively, as an arbitrary condition, the fact that master 100 has established communication with all slaves 200 may be adopted.

[0107] The period for calculating the defect rate can be arbitrarily selected as follows.

[0108] (1) From when it is determined that the number of errors is increasing until now (2) From when the power of the master 100 is turned on until now (3) At predetermined time intervals from when it is determined that the number of errors is increasing The significance may be determined based on the calculated defect rate as follows.

[0109] · Significance "High": The state where the defect rate exceeds the threshold Th2: Immediate countermeasures are required · Significance "Medium": The state where the defect rate exceeds the threshold Th1 and is less than or equal to the threshold Th2: Planned maintenance is required · Significance "Low": The state where the defect rate exceeds 0[%] and is less than or equal to the threshold Th1: A state where noise or the like is occurring (low risk) · Significance "None": The state where the defect rate is 0[%]: Communication is possible normally In addition, if the defect rate is temporarily calculated as a high value at a certain time and then returns to a low value, it can also be regarded as an error that occurred accidentally. That is, in such a case, it may be determined that communication is possible normally.

[0110] The information provided to the user may be varied according to the determined significance.

[0111] Note that the process according to step S5 (calculation of the defect rate and determination of significance) may be executed periodically regardless of the determination in step S2.

[0112] <H. Determination of the acquisition period (step S6)> Next, the details of the process according to step S6 in the process procedure shown in FIG. 7 will be described.

[0113] For example, the error monitoring function 234 included in the communication control circuit 232 of the slave 200 writes the number of errors that have occurred to the error number storage register 236 (see FIG. 2). Here, the upper limit of the number of errors that can be written is determined depending on the data size of the error number storage register 236 to which the error is written.

[0114] Therefore, the master 100 needs to obtain the number of errors generated by the slave 200 so that the number of errors generated by the slave 200 does not reach the upper limit (that is, so that the error generation count storage register 236 does not overflow).

[0115] For example, if the error occurrence number storage register 236 is provided with 8 bits, the maximum number of errors that can be stored in the error occurrence number storage register 236 is 255. If one frame is transmitted in one communication cycle, the upper limit of the error occurrence number storage register 236 will be reached in 255 communication cycles at the earliest. If two frames are transmitted in one communication cycle, the upper limit of the error occurrence number storage register 236 will be reached in 127 (≈255 / 2) communication cycles at the earliest.

[0116] Therefore, the master 100 acquires the acquisition period of the error occurrence count from the target slave 200. More specifically, the acquisition period may be determined according to the number of frames transmitted in one communication period. In the above example, the acquisition period can be calculated as follows: Acquisition period = (upper limit stored in the error occurrence count storage register 236) / (number of frames transmitted in one communication period) x communication period.

[0117] The acquisition period may be determined based on the defect rate calculated in step S5. That is, since the defect rate indicates the frequency at which errors occur, it can be calculated as follows: Acquisition Period = (Upper limit stored in error occurrence count storage register 236) / (Number of frames transmitted in one communication period) x communication period x defect rate. For slaves 200 with a low defect rate, the acquisition period may be set longer.

[0118] When the master 100 acquires the number of error occurrences from the target slave 200, it stores the acquired number of error occurrences and calculates the cumulative value of the number of error occurrences as necessary. In addition, the master 100 instructs the target slave 200 to reset the number of error occurrences it holds. That is, the number of error occurrences detected by the target slave 200 is substantially transferred to the master 100 for each acquisition period.

[0119] FIG. 10 is a diagram for explaining the process related to the acquisition of the number of error occurrences in the communication system 1 according to the present embodiment. Referring to FIG. 10, the number of error occurrences detected by the slave 200 increases over time. The master 100 acquires the number of error occurrences and instructs the reset of the held number of error occurrences for each acquisition period. By the reset instruction, the number of error occurrences held by the slave 200 is reset to zero. As shown in FIG. 10, the acquisition period is determined so that the reset is instructed before the increasing number of error occurrences of the slave 200 reaches the upper limit.

[0120] In this way, the master 100 (the acquisition module 150 shown in FIG. 2) acquires the number of error occurrences at an acquisition period corresponding to the time when the maximum value of the number of error occurrences that can be stored in the error monitoring function 234 of the slave 200 can be reached. In addition, after the master 100 (the acquisition module 150 shown in FIG. 2) acquires the number of error occurrences detected by the error monitoring function 234 of the slave 200, it resets the number of error occurrences held by the error monitoring function 234. By appropriately determining the acquisition period of the number of error occurrences, an overflow of the number of error occurrences in the slave 200 can be prevented, and the number of error occurrences can be reliably acquired.

[0121] <I. Provision of Information Based on the Number of Error Occurrences (Step S7)> Next, the details of the process related to step S7 in the process procedure shown in FIG. 7 will be described.

[0122] (i1: Provision Means) In the communication system 1 according to the present embodiment, information regarding a failure may be provided by any method.

[0123] For example, the information may be provided to a user via the support device 300. When the support device 300 is used as a providing means, the information may be provided via any user interface screen provided by the support device 300, or may be provided by referring to system definition variables or an event log held by the PLC that is the master 100.

[0124] Also, the information may be provided to a user via an HMI (Human Machine Interface) or the like. When an HMI is used as a providing means, the information may be provided via an arbitrary user interface screen provided by the support device 300, or may be provided by referring to system definition variables or an event log held by the PLC, which is the master 100.

[0125] Moreover, by implementing a Web server in the server device 400, the information may be provided to a user or the like via a Web application executed on an arbitrary information processing device. When a Web server is used as a providing means, the information held by the server device 400 may be provided to a user or the like via a Web page configured on the Web server.

[0126] Furthermore, when a Web server is used as the providing means, access to the Web page may be guided by notifying a URL (Uniform Resource Locator) or the like by email.

[0127] (i2:Provided content) The communication system 1 according to the present embodiment can not only notify that some permanent fault has occurred in the network, but also provide information necessary for predictive maintenance. That is, the information regarding the fault may include information used for predictive maintenance of faults that may occur in the network. By providing such information necessary for predictive maintenance, planned maintenance and repairs can be performed before a minor fault develops into a permanent fault.

[0128] Furthermore, in the case where the above-mentioned importance is calculated periodically, information may be provided at the timing when the importance changes to a higher level.

[0129] Fig. 11 is a schematic diagram showing an example of a user interface screen provided by the communication system 1 according to the present embodiment. The user interface screen 500 shown in Fig. 11 is an example when a fault of "high" severity occurs in the network. The user interface screen 500 is provided in the form of a display of the support device 300, a display of the HMI, a Web page from the server device 400 (Web server), or the like. The same applies to the user interface screens shown below.

[0130] The user interface screen 500 includes a status display object 510. The status display object 510 includes a connection relationship object 512 that diagrammatically indicates the connection relationship of the target network. Furthermore, a failure location object 514 is displayed superimposed on the connection relationship object 512 in correspondence with the location identified as the location where the failure has occurred.

[0131] The user interface screen 500 further includes a graph 520 showing the number of errors detected by each port of the slave 200. The horizontal axis of the graph 520 showing the number of errors detected by each port of the slave 200 corresponds to the path along which the frame circulates. The user can grasp the current state of the network at a glance by referring to the status display object 510 and the graph 520 showing the number of errors detected by each port of the slave 200.

[0132] The user interface screen 500 includes a message 516 consisting of textual information provided to the user. The message 516 includes, for example, information indicating the location (node ​​or section) where the failure has occurred, the presumed cause, and information on the severity.

[0133] (i3: Change in the number of errors over time) 12 and 13 are schematic diagrams showing another example of a user interface screen provided by communication system 1 according to the present embodiment. The user interface screens shown in Figs. 12 and 13 show the change over time in the number of errors detected in slave 200.

[0134] A user interface screen 501 shown in Fig. 12 includes, in addition to a status display object 510 similar to that in Fig. 11, a graph 530 showing the number of errors generated by time. The graph 530 showing the number of errors generated by time that are detected between the target slaves 200 (between nodes) per unit time.

[0135] The user interface screen 501 further includes a message 518 consisting of textual information provided to the user. The message 518 includes, for example, information indicating the location (node ​​or section) where the fault has occurred, advice, and information on the severity.

[0136] 13 includes a time-integrated error occurrence count graph 532 in addition to the status display object 510 similar to that in Fig. 11. The time-integrated error occurrence count graph 532 shows the result of integrating the number of errors detected between target slaves 200 (between nodes) over time.

[0137] The user interface screen 502 further includes a message 518 consisting of textual information provided to the user. The message 518 includes, for example, information indicating the location (node ​​or section) where the fault has occurred, advice, and information on the severity of the fault.

[0138] By referring to user interface screen 501 and user interface screen 502, the user can at a glance grasp the change over time in the number of errors occurring in slave 200 or between slaves 200. By checking such a change over time in the number of errors occurring, the user can easily grasp how the number of errors occurring is changing over time. In the examples shown in Figs. 12 and 13, a tendency is shown in which the number of errors occurring increases between 12:00 and 13:00.

[0139] (i4: Accumulative display of error occurrences) FIG. 14 is a schematic diagram showing yet another example of a user interface screen provided by communication system 1 according to the present embodiment.

[0140] 14 includes an accumulated error occurrence count graph 540. The accumulated error occurrence count graph 540 indicates the accumulated value of the number of error occurrences acquired from each of the slaves 200 connected to the network. The accumulated value for each unit time is displayed in a manner that allows the breakdown of the number of error occurrences for each slave 200 to be seen.

[0141] By referring to the accumulated error occurrence count graph 540 shown in FIG. 14, the user can quickly grasp the change over time in the error occurrence count and the slave 200 in which the error occurrence count is being detected in each unit time.

[0142] (i5: Display of error occurrences by node / slave) 15 and 16 are schematic diagrams showing still another example of a user interface screen provided by communication system 1 according to the present embodiment.

[0143] The communication system 1 according to this embodiment detects the number of errors for each port of the slave 200 present on the path that the frame circulates. Therefore, the number of errors detected by each port of the slave 200 may be shown as shown in section-by-section error occurrence count graph 520 in Fig. 15. The horizontal axis of section-by-section error occurrence count graph 520 corresponds to the path, and by looking at section-by-section error occurrence count graph 520, it is possible to know at a glance which port an error is being detected.

[0144] On the other hand, since the target of taking some kind of action is the slave 200 unit, it may be possible to know in which slave 200 the number of error occurrences has been detected. Graph 522 of the number of error occurrences by slave is shown in FIG.

[0145] The slave-specific error occurrence count graph 522 indicates the number of errors detected by each of the slaves 200 (that is, the total number of errors detected at the first port and the second port).

[0146] In addition, in FIG. 15 and FIG. 16, the elements of the displayed graph may be associated with each part of the network configuration (connection relationship object 524).

[0147] In this way, by displaying the number of errors associated with the path through which the frame is transmitted in the network, the user can grasp at a glance where in the network the fault is occurring. Also, by varying the granularity of the display (by port / by slave), appropriate information can be provided according to the user's knowledge level and skill.

[0148] (i6: Dynamic display of the number of errors) Fig. 17 is a schematic diagram showing yet another example of a user interface screen provided by the communication system 1 according to the present embodiment. As shown in Fig. 17, the number of errors may be dynamically displayed to make it easier to understand the change over time.

[0149] FIG. 17 shows an example of animating and displaying the per-interval error occurrence number graph 520 at each of the times t1, t2, and t3. That is, by dynamically changing the display content of the per-interval error occurrence number graph 520 for each time, the user can more easily understand at which time the error occurrence number has increased in which slave (or port).

[0150] (i7: Other display) The error occurrence number obtained from the slave 200 can be provided to the user in an arbitrary display mode, not limited to the above-described user interface.

[0151] <J. Modification example> In addition to the above-described typical embodiments, the following modifications are possible. Note that the following modifications can be applied in any one or a plurality of appropriate combinations.

[0152] (j1: Cooperation between the master 100 and the server device 400) The error occurrence number obtained by the master 100 from the slave 200 may be stored in the main memory 104 and / or the storage 110 of the master 100. However, the master 100 may transmit information such as the stored error occurrence number to the server device 400 at an arbitrary timing and store it in the server device 400. By linking the master 100 and the server device 400 in this way, even if the resources of the master 100 are relatively small, the network monitoring process can be continuously executed.

[0153] (j2: Error monitoring function) In the above description, a configuration example in which the communication control circuit 132 of the master 100 has the error monitoring function 134 has been described. However, the present invention is not limited to this, and the processor 102 of the master 100 may be responsible for a function corresponding to the error monitoring function 134. In this case, the system program 1102 of the master 100 includes instruction codes for realizing a function corresponding to the error monitoring function 134.

[0154] Even when the processor 102 of the master 100 implements a function corresponding to the error monitoring function 134, the communication control circuit 132 of the master 100 may have the error monitoring function 134. That is, the communication control circuit 132 and the processor 102 may each execute processing related to error monitoring.

[0155] (j3: Execution entity of processing) In the above description, an example in which the PLC functioning as the master 100 executes all the processing has been described. However, the present invention is not limited to this, and in addition to the PLC functioning as the master 100, other devices may execute part or all of the processing. For example, as the other device, a support device 300 connected to the master 100 may be used, or any information processing device other than the support device 300 may be used. Further, the processing according to the present embodiment may be realized by using computing resources on the so-called cloud.

[0156] <K. Supplementary Note> The present embodiment as described above includes the following technical ideas.

[0157] [Configuration 1] A communication unit (130) connected via a network (20-1 to 20-4) to one or more slave devices (200), wherein the network is configured such that a frame transmitted from the communication unit returns to the communication unit after circulating through the one or more slave devices, and each of the one or more slave devices includes first error monitoring means (234) for monitoring the occurrence of an error in a received frame. An acquisition means (150) for acquiring the number of error occurrences detected by the first error monitoring means from at least one of the one or more slave devices. A generation means (160) for generating information regarding a possible failure in the network based on the acquired number of error occurrences. The acquiring means acquires the number of error occurrences at a period corresponding to a time period during which the first error monitoring means may reach a maximum value of the number of error occurrences that can be stored.

[0158] [Configuration 2] 2. The communication system according to configuration 1, wherein the acquiring means resets the number of error occurrences held by the first error monitoring means after acquiring the number of error occurrences detected by the first error monitoring means.

[0159] [Configuration 3] the communication unit includes a second error monitoring means (134) for monitoring the occurrence of an error in a received frame; 3. The communication system according to claim 1, wherein the acquiring means starts acquiring the number of error occurrences when the number of error occurrences detected by the second error monitoring means satisfies a predetermined condition.

[0160] [Configuration 4] 4. The communication system according to any one of configurations 1 to 3, further comprising a specifying means (170) for specifying a location where a fault has occurred in the network based on the acquired number of error occurrences.

[0161] [Configuration 5] The communication system according to any one of configurations 1 to 4, wherein the generation means calculates a defect rate of the target slave from a ratio of the number of errors occurring in the target slave to the frames transmitted from the communication unit, and determines the severity based on the calculated defect rate.

[0162] [Configuration 6] 6. The communication system according to any one of configurations 1 to 5, further comprising a notification means (180) for notifying a user of information related to the fault.

[0163] [Configuration 7] 7. The communication system according to any one of configurations 1 to 6, wherein the information regarding the failure includes information used for predictive maintenance regarding a failure that may occur in the network.

[0164] [Configuration 8] A communication control method executed by a communication device (100) connected to one or more slave devices (200) via a network (20-1 to 20-4), the network being configured so that a frame transmitted from the communication device returns to the communication device after making a round trip through the one or more slave devices, each of the one or more slave devices including an error monitoring means (234) for monitoring occurrence of an error occurring in a received frame, A step (S3) of acquiring the number of errors detected by the error monitoring means from at least one of the one or more slave devices; and generating information about a fault that may occur in the network based on the acquired number of error occurrences (S5). The communication control method, wherein the acquiring step includes a step of acquiring the number of error occurrences at a period corresponding to a time period during which the error monitoring means may reach a maximum value for the number of error occurrences that can be stored.

[0165] [Configuration 9] A communication control program (1102) executed on a computer (100) connected to one or more slave devices (200) via a network (20-1 to 20-4), the network being configured such that a frame transmitted from the computer returns to the computer after circulating around the one or more slave devices, each of the one or more slave devices including an error monitoring means (234) for monitoring occurrence of an error in a received frame, the communication control program causing the computer to: A step (S3) of acquiring the number of errors detected by the error monitoring means from at least one of the one or more slave devices; and (S5) generating information about a fault that may occur in the network based on the acquired number of error occurrences. The obtaining step includes obtaining the error occurrence count at a period corresponding to the time at which the error monitoring means can reach the maximum value of the error occurrence count that can be stored, in a communication control program.

[0166] <L. Advantage> In the communication system according to the present embodiment, when a frame is transmitted from the master device to the slave devices connected to the network, all the transmitted frames circulate through all the slave devices and return to the master device. If there is a slave device that cannot correctly receive the frame during the circulation of the frame, correct data cannot be transmitted to the slave device and the slave devices after that. As a result, the control calculation as a PLC cannot be appropriately executed, and it becomes necessary to take measures such as stopping for the control calculation and / or the equipment target.

[0167] The communication system according to the present embodiment monitors the occurrence of failures that can occur in the network by obtaining the error occurrence count from the slave devices. The communication system according to the present embodiment provides the user not only with information for predictive maintenance but also with information for permanent failures. By providing the information for predictive maintenance, the user can plan in advance measures such as repair and component replacement for the network. As a result, the possibility of sudden failures occurring in the network can be reduced. Thereby, the network and the PLC using the network can be stably operated.

[0168] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0169] 1 communication system, 2 upper network, 20 link, 100 master device (master), 102, 202 processor, 104, 204 main memory, 110, 210 storage, 112 local bus controller, 114 functional unit, 116 internal bus, 118 bus, 120 upper network interface, 130, 230 network controller, 132, 232 communication control circuit, 134, 234 error monitoring function, 140 communication circuit, 142, 242, 252 receiving unit, 144, 244, 254 transmitting unit, 150 acquisition module, 160 generation module, 170 identification module, 180 notification module, 200 slave device (slave), 206 control circuit, 220 functional module, 236 error occurrence number storage register, 240 first port, 250 second port, 300 support device, 400 Server device, 410 database, 420 Web server, 500, 501, 502 user interface screen, 510 status display object, 512, 524 connection relationship object, 516, 518 message, 520 graph of number of errors occurring by section, 522 graph of number of errors occurring by slave, 530 graph of number of errors occurring by time, 532 graph of accumulated number of errors occurring over time, 540 graph of accumulated number of errors occurring, 514 fault location object, 1102 system program, 1104 user program.

Claims

1. a communication unit connected to one or more slave devices via a network, the network being configured such that a frame transmitted from the communication unit returns to the communication unit after circulating around the one or more slave devices, each of the one or more slave devices including a first error monitoring means for monitoring occurrence of an error occurring in a frame received; an acquisition means for acquiring the number of errors detected by the first error monitoring means from at least one of the one or more slave devices; generating means for generating information about a fault that may occur in the network based on the acquired number of error occurrences; A communication system, wherein the acquiring means acquires the number of error occurrences at a period corresponding to a time period during which the first error monitoring means may reach a maximum value for the number of error occurrences that can be stored.

2. 2. The communication system according to claim 1, wherein said acquisition means resets the number of errors held by said first error monitoring means after acquiring the number of errors detected by said first error monitoring means.

3. the communication unit includes a second error monitoring means for monitoring occurrence of an error occurring in a received frame; 3. The communication system according to claim 1, wherein the acquisition means starts acquiring the number of occurrences of errors when the number of occurrences of errors detected by the second error monitoring means satisfies a predetermined condition.

4. 4. The communication system according to claim 1, further comprising a specifying unit that specifies a location where a fault has occurred in said network based on said acquired number of error occurrences.

5. The communication system according to any one of claims 1 to 4, wherein the generation means calculates a defect rate of the target slave from a ratio of the number of errors occurring in the target slave to the frames transmitted from the communication unit, and determines the severity based on the calculated defect rate.

6. 6. The communication system according to claim 1, further comprising a notification unit that notifies a user of information related to the fault.

7. The communication system according to any one of claims 1 to 6, wherein the information relating to the fault includes information used for predictive maintenance of faults that may occur in the network.

8. A communication control method executed by a communication device connected to one or more slave devices via a network, the network being configured so that a frame transmitted from the communication device returns to the communication device after making a round trip to the one or more slave devices, each of the one or more slave devices including error monitoring means for monitoring occurrence of an error occurring in a received frame, acquiring a number of errors detected by the error monitoring means from at least one of the one or more slave devices; generating information about a fault that may occur in the network based on the acquired number of error occurrences; The communication control method, wherein the acquiring step includes a step of acquiring the number of error occurrences at a period corresponding to a time period during which the error monitoring means may reach a maximum value for the number of error occurrences that can be stored.

9. A communication control program executed on a computer connected to one or more slave devices via a network, the network being configured so that a frame transmitted from the computer returns to the computer after making a round trip to the one or more slave devices, each of the one or more slave devices including an error monitoring means for monitoring occurrence of an error in a received frame, the communication control program including: acquiring a number of errors detected by the error monitoring means from at least one of the one or more slave devices; generating information about a fault that may occur in the network based on the acquired number of error occurrences; The acquiring step includes a step of acquiring the number of error occurrences at a period corresponding to a time period during which the error monitoring means may reach a maximum value of the number of error occurrences that can be stored.

Images