JPH0578977B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a priority information control circuit for a distributed control communication system. Distributed control communication systems have excellent characteristics in terms of reliability and economy, and have been introduced into local area networks and the like.
In such communication systems, priority control is employed as one of the control methods for integrating continuous synchronous communication such as voice and burst asynchronous communication. That is, it attempts to guarantee synchronization by giving high priority to synchronous communication. As a communication system employing such a control method, there is, for example, Japanese Patent Application No. 57-212364: ``Loop Type Communication System''. Priority communication will be explained using this system as an example. Figure 1 shows the configuration of this system. In the communication system shown in FIG. 1, a clock station 1 and a plurality of node stations 3, 4, 5, 6, and 7 are connected by a loop 2 that transmits signals in one direction. As shown in FIG. 2, the clock station 1 sends out a signal P1 at regular intervals To to activate communication with the highest priority. Node stations 3, 5, 7 having the priority given by signal P1 send out signal blocks B3, B5, B7 as shown in FIG. When clock station 1 then takes the right to transmit, it sends out a signal P2 which activates a communication having the next highest priority after P1, and node stations 2 and 6 send out signal blocks B2 and B6. Similarly, communication with a lower priority is activated by the signal P3. Therefore, since the highest priority communication is activated prior to other communication at the period To, it is possible to accommodate synchronous communication.

FIG. 3 shows the basic structure of a signal block having priority information. Each signal block has a preamble
It consists of PR, start flag SF, synchronization signal bit SY, priority field PI, destination address DA, sender address SA, information I, and end flag EF, and the priority information is written in the PI field. Each node station inputs the priority field PI of the clock station 1 signal block.
monitor and perform communication with priority accordingly.

However, if an error occurs in the priority field PI due to a code error on loop 2, lower-priority communications may be activated before higher-priority communications, which may impair synchronicity guarantees for synchronous communications. Become.

An object of the present invention is to provide a priority information control circuit that does not cause errors in priority control even if a one-shot code error occurs, and to improve the reliability of communication through distributed control. The present invention mutually recognizes the priority of communication between each station based on priority information in the signal frame communicated, and transmits when the priority of its own transmission request is the same as or higher than the recognized priority. In a priority information control circuit for a station in a distributed control communication system that starts control, the transmitter includes a priority information sending circuit that writes a plurality of priorities recognized by the station in a priority information field of a signal frame, The receiving unit includes a priority comparison circuit that compares the received priority information with each other and outputs the one with the highest priority as a comparison result, and a priority that recognizes the comparison result as the priority of the communication system. 1 is a priority information control circuit for a station in a distributed control communication system characterized by comprising a setting circuit;

FIG. 4 shows the PI field of the signal block in the present invention. This PI field is PIA, PIB
Each station, including clock station 1, writes the same priority information into PIA and PIB and sends them out. On the other hand, each node station monitors the PI field of the signal block propagating through loop 2, and if PIA and PIB are the same, the priority indicated by these is recognized as the priority of the communication phase at that time, and PIA and PIB are If they are different, the higher priority is recognized as the communication phase at that time. Therefore, even if a single bit error occurs in the PI field, the transmitting station will not send a communication phase with a lower priority than the signal block.

FIG. 5 shows a first embodiment of the present invention in the transmission line interface section of each station. Note that, to simplify the explanation, the access control unit is omitted.

At the time of transmission, switch 12 is set to the transmission register 15 side, and the signal block in transmission buffer 17 is sent to output terminal 11 on loop 2. At this time, the priority information stored in the priority register 16 in the PI field of the signal block is written into the transmission register 15 twice as PIA and PIB. When receiving, switch 12
is set on the repeater 13 side, and the signal at the input terminal 10 is bypassed after being reproduced and supplied to the output terminal 11. The signal block supplied from the input terminal 11 is input to the reception register 14, and the PI fields PIA and PIB are supplied to the priority comparison circuit 18. The priority comparison circuit 18 compares PIA and PIB and sends the higher priority to the priority setting circuit 19, and the priority setting circuit 19 uses this higher priority information to determine the priority of the communication phase at that time. Set the degree.

Note that this priority information control circuit is not unique to the access method in the cited example, but can also be applied to, for example, a token ring with priority control. Furthermore, it is applicable not only to loop (or ring) communication systems but also to other forms of distributed communication systems. A second embodiment of the present invention in a communication system having a bus configuration is shown in FIG.
In this embodiment, the signal block from transmit register 15 is sent to bus 20 via driver 21, and the signal on bus 20 is provided to receive register 14 via receiver 22.

According to the present invention, even if an error occurs in the PI field, each node station can
Since the higher priority of the PIB is recognized as the priority of the communication phase at that time, the probability that the communication phase will have a lower priority than the priority set by the transmitting station is extremely small, ensuring highly reliable communication. In particular, synchronization for synchronous communication can be more ensured.

[Brief explanation of drawings]

Figure 1 is a diagram showing a loop communication system, Figure 2 is a diagram showing a loop communication system.
The figure shows the signal block diagram on the loop, Figure 3 shows the configuration of the signal block, and Figure 4 shows the structure of the signal block according to the present invention.
Figures 5 and 6 showing the structure of the PI field are block diagrams showing the first and second embodiments of the present invention, respectively. In FIG. 6, 1 is a clock station, 2, 3, 4, 5, 6, 7 are node stations, 14, 15, 16 are registers, 1
7 is a transmission buffer, 18 is a priority comparison circuit, 19
2 shows a priority setting circuit, 20 a bus, 21 a driver, 22 a receiver, and 13 a repeater.

Claims (1)

[Claims] 1. The priority of communication between each station is mutually recognized based on the priority information in the signal frame being communicated, and the priority of the own transmission request is the same as or higher than the recognized priority. In the priority information control circuit of a station in a distributed control communication system that starts transmission control when The receiving unit includes a priority comparison circuit that compares the plural pieces of received priority information with each other and outputs the one with the highest priority as a comparison result, and recognizes the comparison result as the priority of the communication system. A priority information control circuit for a station in a distributed control communication system, comprising: a priority setting circuit for controlling a station;