JPH02295251A - Emergency communication control system with priority of taken bus type local network system - Google Patents

Abstract

PURPOSE:To make an emergency communication in an early stage without waiting for the reception of a token frame by transmitting respective frames on a transmission line forcibly, causing a collision against frames which are being transmitted and interrupting the transmission, and interrupting emergency communications other than an emergency communication with high priority. CONSTITUTION:The system consists of the bus type transmission line 1 and data transmitters 2-1-2-N connected to the transmission line 1, and those respective data transmitters 2-1-2-N has a frame transmitting and receiving function and a frame collision detecting function. Here, when the data transmitters need to have emergency communications and frames are being transmitted on the transmission line 1, the respective frames are transmitted forcibly, a collision against frames being transmitted is caused to interrupt the transmission, and emergency communications other than the emergency communication with priority are interrupted. consequently, the emergency communication is made early without waiting for the reception of a token frame.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a bus-like transmission line, a bus-shaped transmission line,
Data collision due to simultaneous transmission on the transmission path (
Regarding a token bus type local network system, which has a plurality of data transmission devices having a function of detecting collision (collision), and in which the data transmission device transmits data in a frame-by-frame configuration including a preamble at the beginning, in particular an emergency communication control method. Regarding. [Prior Art] Conventionally, transmission control methods adopted in bus-type local network systems include the CSMA method, which transmits frames after confirming that no data exists on the bus, and the CSMA method, which transmits frames after confirming that no data exists on the bus, and the CSMA method, which transmits frames after confirming that no data exists on the bus. The CSMA/CD method, which has a function to detect collisions with frames transmitted by other data transmission devices, is common. However, since it assumes the occurrence of frame collisions, CSMA and C
The SMA/CD method is unsuitable in terms of performance under high loads. For this reason, in a bus type local network system, a method of controlling transmission using a token frame has been considered in which only a data transmission device that has received a token frame is allowed to transmit, and this system is called a token bus type local network system.

[Problem to be solved by the invention]

In the above-mentioned conventional transmission control method using token frames, even if you want to transmit urgently, you cannot transmit until a token frame is received. This method has the disadvantage that it is not possible to perform communications that require urgency, such as forced initialization processing for an information processing system.

An object of the present invention is to provide an emergency communication control system that allows emergency communication to be performed early without waiting for the reception of a token frame. [Means for Solving the Problems] In the priority emergency communication control method in the token bus type local network system of the present invention, when a normal frame for normal communication is being transmitted on the transmission path, the data transmission device Performing emergency communication by forcibly transmitting an emergency frame for emergency communication, causing a collision with a normal frame already being transmitted to interrupt transmission of other data transmission devices, and transmitting a preamble constituting the emergency frame. If collisions no longer occur during the transmission, transmission continues and all emergency frames are sent, and if collisions continue to occur even after the preamble transmission is completed, transmission of the emergency frames is stopped. The data transmission device that controlled and interrupted the transmission retransmits the normal frame destroyed by the collision after the emergency communication is completed.

[For production]

When an emergency communication event occurs from multiple data transmission devices and frames are being transmitted on the transmission path, each frame is forcibly transmitted, causing a collision with a frame that is already being transmitted and interrupting the transmission. , and also interrupts emergency communications other than emergency communications with high priority, so emergency communications can be performed early without waiting for reception of a token frame.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a token bus type local network system showing one embodiment of the present invention. This bus-type local network system is composed of a path-like transmission line 1 and data transmission devices 2-1 to 2-N connected to this transmission line 1, and each of these data transmission devices 2-1 to 2-N. Each of N has a frame transmission/reception function and a frame collision detection function.

The data transmission devices 2-1 to 2-N each have a reception control section 3 that receives a frame transmitted on the transmission path l and determines whether the frame is addressed to itself, and a reception control section 3 that receives a frame transmitted from the control section 6. The transmission control section 4 includes a transmission control section 4 that sends out frames to the transmission path 1, a collision detection section 5 that detects collisions of frames on the transmission path 1, and a control section 6 that controls the entire data transmission device. Then, the reception control section 3, transmission control section 4, collision detection section 5, and control section 6 transmit frames onto the transmission path 1, causing collisions with frames already being transmitted, and transmitting them to other data transmission devices. This constitutes a means for interrupting emergency communication.

Usually, each data transmission device 2-1.2-2,...2-N
has an address on the network to distinguish it from other data transmission devices on the network. Further, data transfer is performed in units of frames. Although one frame is not shown in the figure, it generally includes a preamble, which is data for synchronization, from the beginning of the frame.
Calculated the address of the destination data transmission device, the address of the source data transmission device, the frame type information that distinguishes the types of token frames, response frames, and data frames, the data, and the checksum of the entire transmission frame. Contains FCS. Furthermore, the token frames are transmitted over the network in a predetermined order.

Here, transmission and reception control in the data transmission devices 2-1 to 2-N is performed as follows. First, transmission is started when the control section 6 instructs the transmission control section 4 to transmit, and the transmission control section 4 sends the frame sent from the control section 6 to the transmission path 1. . Next, for reception, the reception control unit 3 always receives frames transmitted on the transmission path l, and if the frame is addressed to itself, it sends the received frame to the control unit 6, and if the frame is addressed to itself, it is sent to the control unit 6. If not, this is done by discarding it.

Also, if frames are simultaneously transmitted from other data transmission devices on the transmission path 1 during transmission and a collision occurs, the collision detection unit 5 detects this and notifies the control unit 6 that a collision has been detected. .

Now, emergency communication according to the present invention is performed as follows.

First, if the data transmission device that is attempting to perform emergency communication has already received a token frame, it performs emergency communication in exactly the same way as a normal transmission operation. Next, as an example of a case where the data transmission device has not received the token frame yet, data transmission device 2-1
A case will be described in which the data transmission devices 2-2 and 2-3 make emergency communications to the data transmission devices 2-5 and 2-6, respectively, when the data transmission device 2-N is about to transmit a data frame to the data transmission device 2-N.

When the data transmission device 2-1 receives a token frame addressed to itself at the reception control unit 3, it sends the received frame to the control unit 6, and the transmission control unit 4 receives the token frame sent from the control unit 6 from the data transmission device 2-1. Send a data frame addressed to N. At this time, the data transmission device 2-2.2-3 starts receiving the frame transmitted to the transmission path 1 by the reception control unit 3, and at the same time, the data transmission device 2-2. The frame is sent from the transmission control unit 4 to the transmission path 1 to forcibly cause a collision. When the collision detection unit 5 detects this collision, the data transmission device 2-1 learns that there is a data transmission device on the network that is attempting to perform emergency communication, and temporarily suspends transmission. In addition, data transmission device 2-2
82-3 detects a collision when it starts transmitting the emergency communication frame, but continues transmitting! ! Continue. Among the data transmission devices 2-2 and 2-3, the data transmission device (in this example, data transmission device 2-3) in which no collision is detected during the preamble transmission period continues transmission and completes the frame. Send data. The data transmission device (data transmission device 2-2 in this example) in which collisions continue to be detected even after the transmission of the preamble is completed temporarily suspends transmission.

On the other hand, when the reception control unit 3 receives this frame for emergency communication, the data transmission device 2-6 sends a response frame to the transmission control unit 3 to notify the data transmission device 2-3 of the reception. Send from. Then, the data transmission device 2-3 receives the response frame from the data transmission device 2-6 using the reception control unit 3, and ends the desired emergency communication.

Next, the data transmission device 2-1, which had interrupted transmission, waits for a certain period of time longer than the maximum time required to complete transmission and reception between the data transmission devices, and then transmits the same data frame to the data transmission device 2-1 again. - Send to N. Further, the data transmission device 2-2, on the other hand, in order to perform emergency communication,
Emergency communication is again made to the data transmission device 2-5 in the same manner as the operation of the data transmission device 2-3.

By performing emergency communications as described above, emergency communications can be made quickly without any inconvenience even if a token frame is not received. [Effects of the Invention] As explained above, the present invention provides a token bus type local network system in which, when an event occurs in which emergency communication is performed from a plurality of data transmission devices, and a frame is being transmitted on the transmission path, the forced By automatically transmitting each frame and causing a collision with a frame that is already being transmitted, interrupting the transmission, and also interrupting emergency communications other than high-priority emergency communications, without waiting for the reception of a token frame. This has the effect that even if multiple emergency communications occur, the emergency communications can be made quickly without any inconvenience.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a token bus type local network system showing one embodiment of the present invention, and FIG. 2 is a block diagram of data transmission devices 2-1 to 2-H. ■・・・・・・・・・・・・・・・Transmission line, 2-
1-2-N... Data transmission device, 3...
・・・・・・・・・・・・・・・Reception control section, 4...
・・・・・・・・・・・・・・・Transmission control section, 5...
・・・・・・・・・・・・・・・Collision detection part,
6・・・・・・・・・・・・・・・・・・Control unit.

Claims (1)

[Claims] 1. A bus-like transmission path and a plurality of data transmission devices connected to this transmission path and having a function of detecting collisions of data due to simultaneous transmission on the transmission path; In a token bus type local network system in which a data transmission device transmits data in a frame-by-frame configuration including a preamble at the beginning, the data transmission device is configured to perform forced transmission when a normal frame for normal communication is being transmitted on the transmission path. perform emergency communication by transmitting an emergency frame for emergency communication, causing a collision with a normal frame already being transmitted and interrupting the transmission of other data transmission devices, and while transmitting a preamble constituting the emergency frame If collisions no longer occur, the transmission is continued and all emergency frames are sent, and if collisions continue to occur even after the preamble transmission is completed, the transmission of the emergency frames is stopped. An emergency communication control method in a token bus type local network system, wherein the data transmission device that interrupted the transmission retransmits the normal frame destroyed by the collision after the emergency communication is completed.