JP2000115205A - Network connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the connector for a bus type network that can detect normal start-up of the bus type network. SOLUTION: A bus type network of a daisy chain system interconnects a plurality of nodes 10a-10d, and the network connector 20 interconnects both ends of the network. When the but type network is normal, a switch 24 is open and data received via 1st and 2nd communication sections 21, 22 are aborted and when a fault takes place in a transmission line, the switch is closed to get through both the 1st and 2nd communication sections 21, 22. Frames received by both the 1st and 2nd communication sections 21, 22 are compared, number of times of same received frames is counted, and when the count exceeds a threshold value, it is judged that each node connection to the network is in an operative state. A judgment means that judges presence of the fault is started after awaiting the judgment of the operative state of each node.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network connection device, and more particularly, to a device for connecting both ends of a bus type network.

[0002]

2. Description of the Related Art As is well known, a bus type network is one type of network. In this network, for example, as shown in FIG. 1, a plurality of nodes 1 are connected by a cable 3 via a built-in communication unit 2. At this time, each node 1 is connected to one or two adjacent nodes 1 so as to take a single series-connected structure as a whole. As a result, the nodes 1 located at both ends of the network are connected to another adjacent node, and the remaining nodes 1 are connected to two adjacent nodes 1.

The communication section 2 has a function of transferring (through) a signal (frame) transmitted from one cable 3 to the other cable 3 and conforms to certain conditions of the transmitted signal ( It has the ability to capture frames (for example, to you). The nodes located at both ends are
Terminate without slew. By passing through in this way, frames output from each node connected to the network can be transmitted to the entire network at high speed.

[0004]

The above-mentioned bus network of the digital chain system has the following problems. That is, when a failure occurs in the transmission system such as a break in a certain cable 3, transmission of a signal is interrupted at the break point, so that a frame cannot be transmitted to the entire network.

[0005] In order to solve this problem, it is preferable to form a loop (ring) network in which the network is formed into a loop. That is, even if one cable breaks, the frame can be sent to the entire network by wrapping around from the opposite side. However, in the case of this loop type network, each node
Since a frame can be transmitted only to an adjacent node, for example, when a frame is sent to a non-adjacent node, the intermediate nodes are sequentially relayed (unlike the through described above, the data is temporarily And then send it out). Therefore, high-speed communication cannot be performed unlike the bus network.

Therefore, the present inventor controls two communication units respectively connected to both ends of the bus type network so as to be able to transmit and receive, a switch connecting the two communication units, and a switching operation of the switch. A first state in which both communication units are shut off by switching a switch, and data received by one communication unit by connecting the two communication units and transferred to the other communication unit for transmission. A network connection device configured to be able to enter the second state is considered (specific configuration will be described in detail in the embodiment).

When such a network connection device is used, the network is apparently in a loop shape (pseudo-loop shape) because both ends of the network are connected by the network connection device. By setting the state, no data is transferred in the network connection device, so that a normal bus type network is obtained. When a transmission line failure occurs, a switch is closed to transfer the received data received by one communication unit to the other communication unit, thereby forming a loop, thereby reliably transmitting a frame to all nodes. Can be made possible. That is, high-speed communication is enabled in a normal state, and network communication can be continued in response to a transmission path failure.

That is, even when a part of the bus-type network is interrupted or the like and transmission through that part is not possible, frames can be transmitted through the network connection device, and the system is resistant to failure. Note that in the event of a failure in this way, strictly speaking, the nodes located at both ends of the failure have constructed and operated a bus network in which both ends are located. In this sense, it is called a pseudo-loop (although it looks like a loop, it is not a loop-type network but is divided at a failure point).

Incidentally, when such a network connection device is actually used, the nodes constituting the network rarely start up (power is turned on) at the same time, but start up sequentially with a time lag. Therefore, until at least all the nodes have risen, at least one of the nodes is off, so that the frame cannot be transferred within that node. on the other hand,
A node that has already started up transmits a frame, so if all the nodes existing on the transmission path between the node that sent the frame and both ends of the network are up, the frame is transmitted to that end point. Although the signal can be received by one of the communication units of the network connection device, the frame does not reach the end point of the network and eventually the communication unit of the network connection device unless at least one node has started up. This phenomenon is the same as when a transmission path failure has occurred after all nodes have started up and a network has been successfully constructed.

Therefore, if the network connection device having the failure detection function is started before all the nodes are started, there is a possibility that any one of the above-mentioned nodes determines the state of the power supply off as a transmission line failure and switches the switch. There is. Then, when all the nodes start up thereafter, since both ends of the bus-type network are connected to form a loop, a frame collision may occur, possibly damaging a system that has constructed the network.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to solve the above-described problems and to provide data connected to both ends of a bus-type network and received from the both ends. In the network connection device that determines the presence or absence of a failure based on the above, it is possible to determine whether all nodes connected to the network are operable at the time of startup of the network, and prevent malfunction. It is to provide a network connection device.

[0012]

In order to achieve the above-mentioned object, a network connection device according to the present invention is a network connection device which can be connected to and disconnected from both ends of a bus-type network. First and second communication units each connectable to a point, determination means for determining the presence or absence of a transmission path failure in the bus-type network based on data received by the first and second communication units, and the determination means Control means for controlling the activation of the device. Then, the control unit compares the frames received from the first and second communication units, and based on the number of times that the frames output from the same node are received by the first and second communication units,
It is configured to determine whether to activate the determination means (claim 1).

In the case of a bus type network, frames transmitted from the same node reach both ends if they are normal. On the other hand, if a transmission path failure has occurred, the frame does not reach at least one end point. Therefore, the determination means determines the presence or absence of a transmission path failure based on whether or not the frame has reached both end points based on the data received by both communication units.

On the other hand, immediately after the network is started, at least one node may be inoperable. That is, such a phenomenon occurs when the power is not turned on. Then, since the transmission path is cut off at the node, the frame transmitted from the activated operable node does not reach at least one of the communication units. Then, when all nodes are in an operable state, the frames transmitted from each node are received by the first and second communication units, respectively.

Therefore, the control means determines whether or not a frame output from the same node is received by the first and second communication units, and based on the number of times that all frames have been received, all the nodes operate. It is determined whether or not it is possible. Then, when it is determined that it is in the operable state, the determination unit is activated. This activation may be performed directly by the control means or indirectly (such as via another means). Further, the activation command may be output from the control means, or the determination means may obtain information on whether or not activation is possible by going to the result of the determination made by the control means.

Here, the number of receptions serving as a criterion, that is, the number of times of determining that an operable state has been reached may be one time or an arbitrary number of times. When the number of times is plural, various judgment criteria can be taken such as limiting to the case where the number of times is consecutively the same, or arbitrarily the number of times reaching the arbitrary number of times without being consecutive. .

Whether or not a frame is output from the same node can also be determined by judging whether or not the entire frame matches. For easy processing, the address of the transmission source is determined. (In this case, it is not necessary to look at specific data or the like).

[0018]

FIG. 2 shows a preferred embodiment of a network connection device according to the present invention and a network in which the device is mounted. First, a description will be given of a network connection device which is a premise of the present invention, and which is capable of controlling the switching between discarding and passing of data received from both ends of the network by forming a bus type network into a pseudo loop.

As shown in FIG. 1, in this embodiment, four nodes 10a to 10d are connected by a cable 12 via a bus network of a digital chain system. The cable 12 is configured using an optical fiber.

As a system for constructing such a digital chain bus type network, for example, at least one
One node can be configured using a PLC. For example, for one master station composed of PLC, for example,
There is a type in which various components such as a plurality of remote I / O slave stations, transmission terminals, programmable displays, and inverters are connected and linked in a digital chain system using a cable composed of a two-core cable or an optical fiber. Further, each node is constituted by a PLC, and the PLC
The CPU units may be connected in a digital chain system using a cable such as an optical fiber to configure a system in which each PLC performs a certain process by performing distributed and cooperative control. Further, instead of connecting the CPU units to each other, an Ethernet unit may be provided in the PLC configuring each node, and the PLC units may be connected via the Ethernet unit on a ten-to-two basis. Of course, other network configurations can be adopted.

Each of the nodes 10a to 10d has a communication unit 13
Is built in, and the communication units 13 of adjacent nodes are connected by a cable 12. For convenience of illustration, the cable 12 is shown by a single line, but each has two built-in paths, up and down. In other words, for example, the cable 12 connecting the first node 10a and the second node 10b is connected from the first node 10a to the second node 10b.
A transmission path for transmission to the second node 10b to the first
Two transmission paths for transmitting to the node 10a are provided. Therefore, no frame collision occurs during transmission through the cable 12.

The communication unit 13 has a function of passing through the transmitted frame as it is and transmitting it to the next node as described later.
Data transmitted by d can be broadcast to other nodes at once. Of course, if the passing frame is addressed to itself, it will be imported into the node,
A predetermined process corresponding to the content of the frame is performed.

Here, in the present invention, one ends of connection cables 14 are connected to the communication units 13 in the first and fourth nodes 10a and 10d at both ends of the bus type network, respectively.
Connect the other end of the connection cable 14 to the network connection device 2
The connection is made to the first and second communication units 21 and 22 in 0. Thereby, the cable 12, the connection cable 14
And the network connection device 20, each node 10
a to 10d are apparently connected in a loop shape.

The first and second communication units 21 and 22
The received frame is sent to the information processing unit (MPU) 23. Further, both communication units 21 and 22
Are connected via a normally open contact switch 24.
Therefore, when the switch 24 is open, the frame sent from the first node 10a is sent to the information processing unit 23 via the first communication unit 21 and discarded there. Similarly, the frame sent from the fourth node 10d is sent to the information processing unit 23 via the second communication unit 22, where it is discarded.

Therefore, in this state, since both ends constituting the network are not connected in the network connection device 20, the network becomes an ordinary Digi-Chain bus-type network, and each node does not collide with frames. High-speed communication is possible with 10a to 10d.

On the other hand, when the switch 24 is closed, the frame transmitted from the first node 10a is transmitted to the first communication unit 21.
Through the switch 24 and the second communication unit 22
From the second communication unit 22 to the fourth node 10d. Similarly, the frame transmitted from the fourth node 10d reaches the first node 10a via the second communication unit 22 → the switch 24 → the first communication unit 21. Thereby, a loop type network is configured.

As described above, by opening and closing the switch 24, it is possible to switch between the bus type network and the loop type network. By adopting a necessary network configuration according to the situation, the advantage of the loop type while maintaining high-speed communication. (Even if a transmission path failure occurs, network communication is possible as it is).

As an example of this use mode, for example, FIG.
As shown in (1), when one cable 12 constituting the transmission path fails, communication between the third node 10c and the fourth node 10d connected via the cable 12 becomes impossible.
In this case, by closing the switch 24,
Communication between the third nodes 10a to 10c and the fourth node 10d can be performed using a transmission system passing through the connection cable 14 and the network connection device 20. When the failure of the cable 12 is recovered, the switch 2
Opening 4 restores the original normal bus network. Thereby, communication between the nodes 10a to 10d can always be reliably performed without causing a frame collision or the like.

The means for judging the presence / absence of a transmission line failure is realized by the information processing unit 23 which receives the data received by the first and second communication units 21 and 22 (the specific configuration will be described later). .

The failure of the cable 12 includes not only a failure such as disconnection of the cable 12 itself, but also a failure of a connection portion (connector) between the cable 12 and the communication unit 13. Further, in the present embodiment, since the cable 12 uses an optical fiber, each of the communication units 13, 21, and 22 communicates with an optical fiber.
It has an electric conversion function. Thus, when the failure of the cable 12 occurs as described above, the failed cable 1
The connection is automatically terminated at the communication units of the third and fourth nodes 10c and 10d connected to the second node. If the cable is an electrical communication medium such as a coaxial cable, a separate terminator is provided, and if a failure occurs as described above,
What is necessary is just to connect to the terminal device.

Next, a specific configuration of each device for constructing the above-described system will be described. FIG.
It shows an example of the internal structure of a to 10d. Basically, each node has the same configuration, and as shown in the figure, is connected to two cables (optical fibers) 13 (in some cases, one is connected to a connection cable 14), and one communication for transmitting and receiving data. The communication unit 12 includes an MPU 15 that transmits and receives data to and from the communication unit 12.

The communication unit 12 includes two data transmission / reception units 12a and 12b connected to the cable 13, a data transmission unit 12c connected to the data transmission / reception units 12a and 12b and mutually transferring data, and a data transmission unit A data processing unit 12d interposed between the unit 12c and the MPU 15 for performing predetermined data conversion and the like. The specific functions and configurations of each unit are as follows.

The data transmission / reception units 12a and 12b are composed of optical-electrical conversion elements for ensuring compatibility between data (light) flowing on the cable 13 and data (electricity) flowing in the node.

As shown in the figure, the data transfer unit 12c receives the data transmitted from one data transmission / reception unit 12a.
The signals are provided to the two adders K1 and K2, transmitted to the data processing unit 12d via the adder K1, and transmitted to the other data transmission / reception unit 12b via the adder K2. Similarly, the data sent from the other data transmission / reception unit 12b is given to two adders K1 and K3,
Is transmitted to the data processing unit 12d via the
3 to one data transmission / reception unit 12a.
Further, the data sent from the data processing unit 12d is added to each data processing unit 12d via adders K3 and K2.
a, 12b.

That is, the communication unit 1 is connected via each cable 13.
2 is sent out to the cable 13 on the opposite side via the adder K3 or K2. That is, the data is transferred (through). Also, since the data is sent to the data processing unit 12d via the adder K1 at the same time, when the sent data is a frame addressed to itself, it can be taken into the inside, that is, into the MPU 15. When transmitting a frame from its own node to another node, the transmission data is transmitted from the data processing unit 12d via the two adders K3 and K2 to the two data transmission / reception units 12a and 12b.
(Cable 13).

Further, the data transfer section 12c shapes a signal when passing through the data transfer section 12c.
Thus, the through data can be transmitted to each node while retaining correct information without distortion.

The data processing section 12d has a function of converting a signal and a data framing function. That is,
The data flowing on the cable 13 is, for example, a continuous code sequence of “1/0”, and the data (signal) in the MPU 15 is a different code. Therefore, the code is converted (function of performing signal conversion). ).

The data flowing on the cable 13 is
As shown in FIG. 5, information such as a destination address, a self-address (source address), and an error check is added before data to be actually transmitted. Such information is unnecessary for processing in the MPU 15. Therefore,
The data transmission / reception unit 12
In the data (frames) sent from a and 12b, the transmission destination address is searched. In the case of the data addressed to itself, the information added before is removed, and only the actual data is extracted and sent to the MPU 15. Of course, those that are not addressed to themselves are discarded as they are. Similarly, necessary information is added before the actual data sent from the MPU 15 and is provided to the data transfer unit 12c. Note that MPU15
Realizes the original function given to the node, such as performing a predetermined cooperative operation while transmitting / receiving data to / from another node.

FIG. 6 shows an example of the internal structure of the network connection device 20. As shown in the drawing, first and second data transmitting / receiving units 21a and 22b are connected to each connection cable 14.
Is connected. These two data transmitting / receiving sections 21a, 21
Like the data transmission / reception unit 12a installed in the node, the optical module 2a is also configured by an optical module having a function of performing optical-electrical conversion.

The data (light) received by the first data transmission / reception section 21a is converted into an electric signal, and is converted into an electric signal.
1b and sent to the data transfer unit 25. The data (light) received by the second data transmission / reception unit 22a is converted into an electric signal, and the second data processing unit 21b and the data transfer unit 25
Sent to

In the data transfer unit 25, in addition to the function of shaping the signal, the data received from the first data transmission / reception unit 21a is transferred (through) to the second data transmission / reception unit 22a as it is, and the data is transmitted to the second data transmission / reception unit 22a. Is transferred (through) to the first data transmitting / receiving unit 21a as it is. At this time, the first and second data transmission / reception units 21a, 22
a, the first and second changeover switches 24
a and 24b are provided to allow or stop the above transfer processing. The two changeover switches 24a and 24b used in the present embodiment select one of two inputs (points a and b) and output one of the inputs (point c). Is connected to the output of the data transfer unit 25, and the other input terminal (point b) is connected to the outputs of the first and second data processing units 21b and 22b.

Further, both changeover switches 24a, 24
Switching of b is controlled by a control signal sent from the information processing device 23. Therefore, by connecting both the changeover switches 24a and 24b to the other input terminal b point side, the first data transmission / reception unit 21a and the second data transmission / reception unit 22a can be disconnected (switch open), and the through operation can be performed. Can be suppressed. Each data transmitted via the connection cable 14 is transmitted to the first and second data transceivers 2.
1a and 22a. Accordingly, a bus network of the digital chain system can be constructed.

On the other hand, both changeover switches 24a and 24b are
By connecting to the one input terminal point a side, the first data transmission / reception unit 21a and the second data transmission / reception unit 22a can be connected (switch closed) and transferred (through).

The first and second data processing units 21b, 2b
The basic function 2b has a signal conversion function and a data framing function, similar to the data processing unit 12c installed in the node. As a reception mode, it is possible to switch between an address mode in which only a frame addressed to itself is received and a 0 mode in which all frames are received. Further, it receives data (various command commands, etc.) sent from the information processing unit 23, performs signal conversion and framing processing on the data, and sends it to each node (actually, from each of the changeover switches 24a, 24b). Connection cable 14 via each data transmission / reception unit 21a, 21b
To be sent).

The information processing device 23 sends the above-mentioned control signal, and outputs the first and second changeover switches 24a and 24a.
b has a function of switching control. This control signal is, of course, to select the other input point b when it is desired to construct a normal digital chain bus type network, and to transmit the control signal through the network connection device 20 when it is desired. Is controlled to select one input point a.

Then, when to output the switching control signal specifically, it can be determined based on, for example, data flowing through the network provided from each of the data processing units 21b and 22b.
As an example, it is possible to determine whether or not a failure has occurred in a part of the network, and when it is determined that a failure has occurred, it is possible to switch to one input unit point a side.

Whether a failure has occurred can be determined, for example, by receiving information on the occurrence of a failure signal from any node. Further, since the frame transmitted from each node always reaches both ends of the network, it is taken into the information processing device 23 via the first and second communication units 21 and 22. Therefore, when a frame is received from only one communication unit side,
It can be determined as a failure. The following various methods can be further applied as a failure detection method using the fact that the signals are always received by both communication units.

That is, the first and second communication units 21 and 22
The received frames are compared with each other, and when the same frame is received, it is determined that the frame is normal, and when the same frame cannot be received, it is determined that a failure has occurred. Judgment is made based on the fact that the frame was received without looking at the contents of the frame. After the reception by one communication unit, the frame is received by the other communication unit within a fixed time (maximum non-transmission time set by the communication protocol + α). Is determined, and if not received, a failure is determined. The number of frames continuously received by one communication unit is counted, and when the number of frames is equal to or more than a certain number, it is determined that a failure has occurred.

Also, instead of being based on the frame transmitted from each node as described above, for example, the information processing device 2
3 can transmit a test frame (data) from one communication unit side and determine whether there is a failure based on whether or not it can be received by the other communication unit. In this case, 2
It is significant that input changeover switches 24a and 24b are provided so that a frame from the information processing device 23 can be transmitted. Of course, other methods may be used. It is the determining means of the present invention that executes these various methods.

In correspondence with the block diagram shown in FIG. 2, the first data transmitting / receiving unit 21a and the first data processing unit 2
1b constitutes the first communication unit 21, and the second data transmission / reception unit 2
2a and the second data processing unit 22b constitute the second communication unit 22. Furthermore, first and second changeover switches 24a and 24b
Constitute the switch 24. The switch 24 may include the data transfer unit 25 as a component. In addition, the first and second changeover switches 24a, 24b
As described above, a switch for selectively selecting and outputting two inputs is used. This is because a frame can be transmitted from the information processing device 23 to each node as described above. The present invention is not necessarily required to have such a configuration, and may be any device that can switch between data through and data discarding, such as a simple ON-OFF switch.

The information processing device 23 has a monitor 26
Is connected, it is possible to display, for example, data collected from each node and to display the operation state of the node.

Further, in this embodiment, two communication units 21 and
2 is provided. Thereby, both end points of the bus network can be connected to different communication units. The data to be sent to the information processing unit 23 is not the data whose waveform has been shaped by the data transfer unit, but is the data received via the first and second data transmission / reception units 21a and 22a. In other words, in the case of a node, noise or the like may be caused by transmitting (transferring) on a network, and if the data is transferred as it is, data may be distorted and erroneous data may be generated. Therefore, it is necessary to shape the waveform in the data transfer unit. On the other hand, in the case of the network connection device, since the data to be sent to the information processing device 23 is not transferred thereafter, it can be sufficiently analyzed without performing waveform shaping.
Of course, if it is desired to shape the waveform, for example, the signal may be branched from between the output of the data transfer unit 25 and the changeover switches 24a and 24b and sent to the data processing units 21b and 22b, or a processing unit for separately shaping the waveform may be provided. Good.

In the above-described embodiment, the device constituting the node is a PLC, but the node to which the present invention is applied is not limited to this, and it goes without saying that various devices can be used. .

Next, a description will be given of a configuration for detecting whether or not all nodes have become operable, which is a control means which is a configuration of a main part of the present invention. First and second communication units 21,
The information processing unit 23 receives the received data (frame) received via the communication unit 22, and the information processing unit 23 determines whether or not all the nodes have become operable according to the reception state of the frame, and becomes possible. When it is determined that the transmission path has failed, the above-described monitoring system for the presence or absence of a transmission line failure is operated.

That is, even one of the nodes connected to the bus-type network is inoperable (power supply is off).
f), the frame transmitted from the node is the first frame
It is not received by at least one of the second communication units 21 and 22. As an example, as shown in FIG.
If b is off, the frame transmitted from the first node 10a is received only by the first communication unit 21, and the third and fourth frames are transmitted.
The frames transmitted from the nodes 10c and 10d are received only by the second communication unit 22. On the other hand, all nodes 10
When the nodes a to d become operable, the frames transmitted from the nodes 10a to 10d are the first and second frames.
These are received by the communication units 21 and 22, respectively. Therefore, the frames received by the first and second communication units 21 and 22 are compared, and if they match, it is determined that all the nodes have become operable. Further, in the present embodiment, it is determined that the operable state has been reached only when the number of times of matching has continued a predetermined number of times (for example, five times). This makes it possible to more accurately detect that the operable state has been reached.

As a specific configuration, as shown in FIGS. 2, 3, 6, and 7, the counter 30 and the first and second buffers 36 and 37 are connected to the information processing section 23, The frames received by the first and second communication units 21 and 22 are stored in the first and second buffers 36 and 37, respectively. Then, the information processing section 23 includes the first and second buffers 36 and 37.
Are compared to determine whether they match, and if they match, the counter 30 is incremented. As a result, the number of times of matching is stored in the counter 30, so that the information processing section 23 looks at the counter value, and when the counter value is equal to or larger than the threshold value, determines that all nodes are in the operable state. I have to. The specific determination process is executed by executing the flowchart shown in FIG.

That is, as shown in the figure, when a frame is received, it is determined which of the first and second communication units 21 and 22 has received the frame (ST1, ST2).
Then, when the frame is received by the first communication unit 21, the frame received this time is compared with the frame previously received by the second communication unit 22 stored in the second buffer 37 (S
T3) If they match, the counter 30 is incremented (ST4). On the other hand, when the frame is received by the second communication unit 22, the frame received this time is compared with the frame previously received by the first communication unit 21 stored in the first buffer 36 (ST5). If so, the counter 30 is incremented (ST6). In the case of non-coincidence, no processing is performed on the counter.

After the above-described processing, the received frame and the communication unit received this time are stored in the buffer as the previously received frame (ST7). That is, the first communication unit 21
, The data is stored in the first buffer 36,
When received by the communication unit 22, the data is stored in the second buffer 37. Next, the counter value is compared with a threshold value (ST
8) If less than the threshold, return to step 1 and wait for reception of the next frame. If the value is equal to or larger than the threshold value, it is determined that all the nodes are in the operable state, and the process is terminated. Actually, thereafter, a normal transmission path failure monitoring algorithm is started. Although not specifically shown, the counter 30 is initially set to 0 as an initial setting.

Further, in the above-described embodiment, it is not always necessary that frames coincide with each other. Although it is determined that the node becomes operable, the present invention is not limited to this, and the frames received by the first and second communication units 21 and 22 are continuously matched more than a predetermined number of times. Then, it may be determined that all nodes have become operable.

In such a case, basically, in the same manner as in the above-described embodiment, it is determined which communication unit has received the frame, and the other communication unit compares the received frame with the previously received frame. If so, the counter is incremented. On the other hand, if it does not match the previously received frame, the counter is set to 0. By adding such a processing step, the counter value becomes the number of times of continuous matching. Also, the received frame and the communication unit received this time are stored in a predetermined buffer as needed for the next comparison. Then, the counter value of the counter 30 is compared with the threshold value. If the difference is less than the threshold value, preparation is made for reception of the next frame.

A specific flowchart for realizing such a function can be as shown in FIGS. 9 and 10, for example. That is, first, it is determined which communication unit has received the frame (ST11, ST1).
2) If it is received by the first communication unit 21, step 1
Proceeding to 3, it is determined whether or not the second buffer 37 is empty. If a frame is stored in the second buffer 37, there is a frame previously received by the second communication unit 22 (a match / mismatch determination has not been made). The process proceeds to compare the frame stored in the second buffer 37 with the currently received frame.

If they match, the counter is incremented (ST15), and the compared frame stored in the second buffer 37 (the frame previously received by the second communication unit) is deleted (ST15). ST16). On the other hand, if the received frame does not match the previously received frame, the counter is set to 0 (ST17), and the frame received by the first communication unit 21 this time is stored in the first buffer 36 (ST17).
18). The stored frame is used for comparison with a frame received by the second communication unit next.

If there is no frame in the second buffer 37 in the determination at step 13, the first communication unit 21 can determine that the frame has been received first. Then, the frame received this time is stored in the first buffer 36.

On the other hand, the received frame is
In the case of (1), the process proceeds to step 19 in the branch determination of step 12, and determines whether the first buffer 36 is empty. If a frame is stored in the first buffer 36, there is a frame previously received by the first communication unit 21 (a match / mismatch determination has not been made). The process proceeds to compare the frame stored in the first buffer 36 with the currently received frame.

If they match, the counter is incremented (ST21), and the compared frame stored in the first buffer 36 (the frame previously received by the first communication unit) is deleted (ST21). ST22). On the other hand, when the frame does not match the previously received frame, the counter is set to 0 (ST23), and the frame received by the second communication unit 22 this time is stored in the second buffer 37 (ST23).
24). The stored frame is used for comparison with the next frame received by the first communication unit.

If there is no frame in the first buffer 36 in the judgment at the step 19, it is possible to judge that the frame has been received first by the second communication unit 22 side this time. And save the frame received this time in the second buffer 37.

When the received frames do not match by executing each of the above-described processes, the counter is reset, and the counter value becomes the number of times of continuous matching. Therefore, the processing (save / delete) for the first and second buffers 36 and 37 is executed (ST16, ST18, ST2).
(2, ST24) After that, the counter value of the counter 30 is compared with the threshold value (ST25). If it is less than the threshold, the process returns to step 11 to prepare for the next frame reception.

Furthermore, in each of the above-described embodiments, the match / mismatch of the frames is checked. However, the present invention does not always need to compare the entire frames. That is, for example, when a frame output from a certain node reaches the first and second communication units 21 and 22, the transmission paths are connected, and it can be determined that all the nodes are in an operable state. Therefore, it is determined which node is the transmission source (identified from its own address), and only the information of which node is transmitted is stored. It may be determined whether or not the node has become operable. Judging based on the information of the transmission source node without comparing the entire transmitted data in this way can be realized by simple processing.

[0069]

As described above, in the network connection device according to the present invention, by providing the predetermined control means,
It can be determined whether all nodes connected to the network are operational. Therefore, the judging means for monitoring the presence or absence of the transmission path failure can be prevented from malfunctioning by starting after waiting for the judgment result of the control means (that all the nodes become operable).

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a conventional bus network.

FIG. 2 is a diagram showing an example of a bus type network in which a network connection device according to the present invention is mounted.

FIG. 3 is a diagram showing an example of a bus network in which the network connection device according to the present invention is mounted.

FIG. 4 is a diagram illustrating an example of an internal structure of a node.

FIG. 5 is a diagram illustrating an example of a data structure of a frame flowing on a network.

FIG. 6 is a diagram showing an embodiment of a network connection device according to the present invention.

FIG. 7 is a diagram illustrating a startup state in a bus network in which the network connection device according to the present invention is mounted.

FIG. 8 is a flowchart illustrating functions of an information processing unit that is a main part of the first embodiment of the network connection device according to the present invention.

FIG. 9 is a part of a flowchart showing a function of an information processing unit in the modification.

FIG. 10 is a part of a flowchart showing a function of an information processing unit in the modification.

[Explanation of symbols]

 Reference Signs List 20 network connection device 21 first communication unit 22 second communication unit 23 information processing device (judgment means, control means) 24 switch 24a first changeover switch 24b second changeover switch 30 counter 36 first buffer 37 second buffer

Claims (1)

[Claims] 1. A network connection device that can be connected to and disconnected from both end points of a bus-type network, comprising: first and second communication units respectively connectable to the both end points; and the first and second communication units. A determination unit configured to determine the presence or absence of a transmission path failure in the bus-type network based on data received by the unit; and a control unit configured to control activation of the determination unit. The control unit includes the first and second control units. And comparing the frames respectively received from the communication units, and determining whether to activate the determination unit based on the number of times the frames output from the same node are received by the first and second communication units. A network connection device, characterized in that: