JPH053939B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is a distributed control system connected by communication lines, and relates to a communication control system in which communication systems are duplicated.

(Prior Art) A distributed control system is a system that reduces the risk of system failure by distributing functions compared to a centralized control system, and has been widely used in recent years. In a distributed control system, a plurality of stations each having a certain function are connected through communication lines. In this type of distributed control system, in addition to sending and receiving information for control, the operating status of each station (normal or abnormal) is
Requires functionality for monitoring. Typically, this monitoring function is located at a station with man-machine interface functionality (monitoring station).

By the way, when monitoring the operating status of each station, the status of the station is whether the data link level is functioning properly or not.
In addition to monitoring abnormal conditions, it is also necessary to monitor the operating state of a processor (application processor) that performs application-level processing. Furthermore,
In order to increase the reliability of data communication between stations, duplication of communication lines is performed.

(Problems to be Solved by the Invention) Conventionally, as a duplication system for this type of communication line, a system in which the physical layer and below are duplexed is used. In this type of system, if the first system fails at one station, and then the second system fails at another station, the station that subsequently failed will be able to confirm that the first system is normal. However, it is considered a fail, and data communication becomes impossible.

The present invention has been made in view of these points, and its purpose is to realize a communication control system that allows reliable data communication even if one of the systems fails.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, adopts a token pass method as a line access method for each station connected to a bus in a bus-based local area network. The media access control layer and below of the data link layer of each station are dually systemized, and two live lists are provided in each station to correspond to the dual system.
The data link layer supports these live lists, checks the status of both live lists when a communication request occurs, and selects and uses one system if the destination is normal on both live lists. The system is characterized in that when only the destination in one live list is normal, a normal system is selected and used, and when the destinations in both live lists are abnormal, abnormal processing is performed. .

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 6 is a diagram showing the configuration concept of a communication control system according to the present invention. In the figure, STN ₁ to
STNn (n is an integer) is the station, BUS1,
BUS2 is a communication line for dual system communication. Line access control between stations is performed by a token pass (also known as baton pass) method, which will be described later. The token pass method is a method in which line control rights (called tokens) are transmitted one after another in a predetermined order using command frames (token pass commands), as shown in FIG. In the token pass method, only a station with a token can output a signal on the communication line. When each station receives the token, it sends a command if there is a transmission request, receives a response if necessary, and passes the token to the next station. If there is no transmission request, the station immediately passes the token to the next station. This type of line access is called the token pass method. FIG. 8 is a diagram showing the flow of command frames on the communication line.

In the token pass method, whether the token has been transmitted to the next station is determined by whether a command frame (including the token pass) is sent on the communication line within a certain period of time after the token pass command is sent. . In the distributed control system, there are three ways to connect the stations: star type, loop type, and bus type. The present invention is based on the case of a bus-type connection form.

In the communication control system shown in FIG. 6, as shown in FIG. 7, each station receives a token in turn and passes the token to the next station to control access to the line. FIG. 9 is a diagram showing an example of the structure of a token pass frame output on a communication line. In the figure,
Preamble (PREAMBLE) is the cue area,
F is the flag sequence area, DA is the destination address (DESTINATION ADDRESS) area where the address indicating the destination is stored, SA is the source address (SOURCE ADDRESS) area where the address indicating the source is stored, and C is the A control field for packet transmission control, FCS, is an area where a frame check sequence is stored, and a postamble (POSTAMBLE) is an area indicating the end of a frame. The number shown below each area indicates the number of bits. Note that when data is placed in the frame shown in the figure, the data is inserted between the C area and the FCS area.

FIG. 10 is a diagram showing an example of the configuration of the control field C of the token frame described above.
In the example shown, control field C is 8
The seventh bit (shaded area in the figure) contains modification bit data that modifies the normal/abnormal state of the application processor (main processor) of the station. When the seventh bit _D6 is "1", the station is in a READY state, and when it is "0", it is in a NOT READY state. In the token pass method, the D _6- bit data of a normal station is always "1", otherwise it is "0".

As mentioned above, the communication control system according to the present invention performs line access using the token pass method, so one of the stations receives the token, and the remaining stations constantly use the communication line. Monitor the bus status during reading.

FIG. 11 is a diagram showing an example of a station logical configuration according to the present invention. In the figure, 1 is the logical link control layer, 2 and 3 are the first and second layers, respectively.
4 and 5 are media access control layers provided for each communication line BUS1 and BUS2, and 6 and 7 are live lists provided for each communication line BUS1 and BUS2 (details will be described later). Physical layers 8 and 9 directly connected to the communication lines BUS1 and BUS2 are physical layer interfaces that control the exchange of signals between these physical layers 6 and 7 and the media access control layers 4 and 5, respectively.
As is clear from the figure, in the duplex system according to the present invention, the media access control layer 4,
5 or less will be duplicated.

FIG. 1 is a block diagram showing an example of the internal configuration of a station according to the present invention. In the figure,
IB is an internal bus, 11 is a processor (main processor) connected to internal bus IB, 12 is memory connected to internal bus IB, and 13 is a signal between input/output device (I/O) 14 and internal bus IB. It is an I/O interface that exchanges information. 15 is a communication control device whose one end is connected to the internal bus IB and the other end is connected to the first and second physical layers (coupler) 6 and 7, and which controls the flow of command frames and data on the communication lines BUS1 and BUS2. This is the part that characterizes the present invention. The duplication of the communication system is performed for the media access control unit and subsequent parts within the communication control device 15.

FIG. 2 is a specific configuration diagram showing one embodiment of the communication control device 15. As shown in FIG. In the figure, 20 is a dual port RAM that interfaces with the main processor (application processor) 11 (see Figure 1) in the station.
The dual port RAM 20 is composed of a transmission buffer 21, a reception buffer 22, live lists 23 and 24 for two channels, and the like. Live list 23 is for the first communication line BUS1,
The live list 24 is for the second communication line BUS2.

31 is a microprocessor for logical link control, 32 is a ROM in which sequences for communication control are stored, and 33 is a first media access control unit that performs transmission/reception control and token pass control for the first communication line BUS1. , 34 is a second media access control unit that performs transmission/reception control and talk path control for the second communication line BUS2.

IB' is an internal bus within the communication control device that connects the dual port RAM 20, microprocessor 31, ROM 32, and first and second media access control sections 33 and 34 to exchange signals. 34 is the first media access control unit 3
3 is a physical layer interface section connected between 3 and physical layer 6; 36 is a second media access control section 3;
4 and the physical layer 7. Physical layers (couplers) 6 and 7 are directly connected to first and second communication lines BUS1 and BUS2, respectively. That is, in the system shown in the figure, the first communication line system and the second communication line system are completely independent. The operation of the device configured as described above will be explained as follows.

The communication control device 15 connects the communication line BUS1 or
When a frame on BUS2 is received, it is checked whether the frame is a token pass frame. When confirming that the frame is a token pass frame, the communication control device 15 creates a live list indicating the normal/abnormal state of each station from the source address SA of the frame.
The created live list is stored in the live list 23 or 24 in the dual port RAM 20 in the communication control device 15.

FIG. 3 is a diagram showing an example of the configuration of a live list. The live list shown in the figure has a maximum configuration of 32 stations, and a 1-byte data area is allocated to each station. A live list is created for each station, and all bytes of a station whose data link level has failed are set to 0. These live lists use a total of two bits, a bit indicating the data link level status and a bit indicating the application level status, as bits indicating the station status for each station.
In this case, bits other than the two specific bits are ignored.

FIG. 4 is a flowchart showing the operation of the system described above. A shows the operation when the token pass frame is sent, and b shows the operation when the token pass frame is received. At the time of sending, the communication control device 15 sends the token pass frame (see FIG. 9).
Enter the next destination station number in the DA area, SA
Write the station number of the source (your own station number) in the area. Next, the application status is received from the main processor (application processor) 11, and when the main processor 11 is in the ready state, the Hex60
When in the not-ready state, after writing Hex20 into the C area of the token pass frame, it is sent onto the communication line BUS1 or BUS2.

Next, the operation at the time of reception will be explained. When the communication control device 15 receives a frame, it first checks whether the frame is a token pass frame. If it is a token pass frame, after initializing the live list for the station between the SA area and DA area in the token pass frame to "0", add control feed C to the live list corresponding to the SA area. Performs the action of writing the contents.

The microprocessor 31 in the communication control device is
In this way, the first and second live lists 2
Check the status stored in 3 and 24. First, it is checked whether the destination station is in the READY state on the first live list 23. If it is in the ready state, the function of the first communication line system is normal, so there is no need to check the function of the second communication line system, and a transmission request is made to the first media access control unit 33. A command is issued and a token pass frame is sent from the media access control unit 33 to the next station.

If the destination station is not ready on the first live list 23,
This means that the communication line system is out of order for some reason. In this case, it is checked whether the destination station is in a ready state on the second live list 24. If it is in the ready state, the function of the second communication line system is normal, so a transmission request command is issued to the second media access control unit 34, and the transmission request is sent from the media access control unit 34 to the next station. Sends a token pass frame. That is, according to the present invention, even if the first communication line system fails, the purpose can be achieved using the second communication line system.

If the destination station is not in the ready state on the second live list 24, there is an abnormality in both communication line systems, and communication is impossible. Therefore, in this case, processing is stopped.

(Effects of the Invention) As explained in detail above, according to the present invention,
The station's media access control unit and below have a redundant configuration, and each line has an independent live list for monitoring the operating status of the communication line system, and communication between each station is done using a token pass method. By doing so, it is possible to realize a communication control system that can perform reliable data communication even if one of the systems fails.

[Brief explanation of drawings]

1 is a diagram showing an example of the internal configuration of a station according to the present invention, FIG. 2 is a specific configuration diagram showing an embodiment of a communication control device, FIG. 3 is a diagram showing an example of the configuration of a live list, 5 is a flowchart showing the operation of the system of the present invention. FIG. 6 is a diagram showing the configuration concept of the communication control system according to the present invention. The figure shows a token pass sequence, FIG. 8 shows a flow of frames on a communication line, FIG. 9 shows an example of the structure of a token pass frame, and FIG. 10 shows an example of a control field structure. , FIG. 11 is a diagram showing an example of the logical configuration of the station according to the present invention. 1...Logical link control layer, 2, 3, 23,
24... Live list, 4, 5... Media access control layer, 6, 7... Physical layer, 8, 9... Physical layer interface, 11... Processor, 12
...Memory, 13...I/O interface, 1
4...Output device, 15...Communication control device, 20...
... Dual port RAM, 21 ... Transmission buffer, 22 ... Reception buffer, 31 ... Microprocessor, 32 ... ROM, 33, 34, ... Media access control section, 35, 36 ... Physical layer interface part, IB, IB'...internal bus, BUS
1. BUS2... Communication line, ST ₁ ~ STn... Station.

Claims (1)

[Claims] 1. In a bus-based local area network, the token pass method is adopted as the line access method for each station connected to the bus, and the data link layer of each station below the media access control layer is dual-systemized. Two live lists are set up in each station in response to heavy systemization, and the data link layer supports these live lists. When a communication request occurs, it checks the status of both live lists and updates the data on both live lists. If the destination is normal, select and use one of the systems, if only the destination in one live list is normal, select and use the normal system, and if the destination in both live lists is abnormal. A communication control system characterized in that the communication control system is configured to handle an abnormality in the event of an abnormality.