JPH0484531A - Communication system for local network system - Google Patents

Abstract

PURPOSE:To attain immediate emergency communication without reception of a token frame by sending a frame forcibly when the frequency to be sent exists on a transmission line so as to cause collision. CONSTITUTION:When a data transmitter 2-1 desired emergency communication and a reception control section i-1 does not receive a token frame, while a frame is sent by other data transmitter 2-j on a transmission line under the control of a control section i-2, a new frame is sent forcibly from a transmission control section i-3. Then collision with a frame having been already sent is caused. Moreover, a collision detection section j-4 of other data transmitter 2-j detects the collision to interrupt the transmission, a transmission control section i-3 makes own emergency communication and a token frame is sent to abort the token after the end of emergency communication. Thus, even when no token frame is received, emergency communication is implemented immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication method for a local network system, and more particularly to a communication method for a local network system for performing emergency communication in a token bus type local network.

[Conventional technology]

The transmission control methods adopted in the communication methods of conventional bus-type local network systems include the C8MA method, which transmits a new frame after confirming that there is no data on the bus, and the C8MA method, which transmits a new frame after confirming that no data exists on the bus, and the C8MA method, which transmits a new frame after confirming that no data exists on the bus. The C8MA/CD method, which has a function of detecting when a frame has collided with a frame transmitted by another data transmission device, is common.

However, since the C8MA, C8MA, and /CD methods are based on the assumption that frame collisions will occur, performance under high loads deteriorates in network systems that require a certain limited response time. It's inappropriate.

For this reason, in bus-type local network systems, there is a transmission control method using token frames in which only the data transmission device that has received the token frame is allowed to transmit. It's called a system.

[Problem to be solved by the invention]

In the communication method of the conventional local network system described above, even if you want to send something urgently, you cannot send it until a token frame is received. The disadvantage is that it is difficult to perform communications that require urgency, such as forced initialization processing.

An object of the present invention is to forcibly transmit a frame when there is a frame being transmitted on a transmission path and cause a collision, thereby interrupting other transmissions and causing the user to perform his own emergency communication. An object of the present invention is to provide a communication method for a local network system that allows immediate emergency communication even without receiving a frame.

[Failure to solve the problem]

A communication system for a local network system according to a first aspect of the present invention includes a transmission path of a bus and a plurality of data transmission devices connected to the transmission path, and each of the data transmission devices transmits data via the transmission path. In a communication method of a token bus type local network system that has a function of mutually transmitting data frame by frame and detecting data collision due to simultaneous transmission, one of the data transmission devices is When a frame is being transmitted on the road, forcibly transmitting a new frame and causing a collision with a frame already being transmitted, thereby interrupting the transmission of the other data transmission device,
It is configured by performing its own emergency communication and, after completing the emergency communication, transmitting a token frame and relinquishing the transmission right.

Further, a communication system for a local network system according to a second aspect of the invention includes a transmission path of a bus and a plurality of data transmission devices connected to the transmission path, and each of these data transmission devices is connected to the transmission path. In the communication method of a token bus-type local network system that transmits data in frames to each other via a network and has a function that can detect collisions of data due to simultaneous transmission, (A) perform emergency communication. When the first data transmission device has not received a token frame and the frame of the second data transmission device that has received the token frame is being transmitted on the transmission path, a new frame is forcibly generated. (B) the second data transmission device that detects the collision interrupts its own transmission; (C) the second data transmission device detects the interruption of its transmission; The first data transmission device performs its own emergency communication, and (D) after the emergency communication is completed, the first data transmission device transmits a token frame and relinquishes the transmission right. has been done.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a local network system to which the present invention is applied.

The local network system shown in FIG. 1 is of a token bus type, and includes a transmission path 1 on the bus and a plurality of data transmission devices 2-1, 2-2.・・・
...2-1. ...2-j.

...2-N.

And data transmission device 2-1.2-2.・・・・・・
Data transmission devices 2-t and 2-j, which are arbitrary two of data transmission devices 2-N, mutually transmit data in frame units via transmission path 1, and detect data collisions due to simultaneous transmission. It has the ability to

Further, FIG. 2 is a block diagram showing an example of the data transmission device 2-i of this embodiment.

When the data transmission device 2-i wants to perform emergency communication,
As shown in FIG. 2, if the reception control unit i-1 does not receive the token frame, the frame is transmitted by another data transmission device 2-j on the transmission path 1 under the control of the control unit i-2. 2-j, the transmission control unit i-3 forcibly transmits a new frame and causes a collision with the frame already being transmitted, so that the other data transmission device 2-j that is currently transmitting The collision detection unit j-4 detects the collision and interrupts the transmission, and the transmission control unit i-3
This allows the user to perform his own emergency communication, and after completing the emergency communication, sends a token frame and relinquishes the transmission right.

The communication method of the local network system of this embodiment will be described in detail below, using communication between data transmission devices 2-i and 2-j as an example.

Data transmission device 2+, 2J is network"
In order to distinguish it from other data transmission devices, the network has an address of 'two'.

Further, data transfer is performed in units of frames, and each frame includes the address of the data transmission device 2-i that is the source, the address of the data transmission device 2-j that is the destination, a token frame, and a response frame.

Frame identification information that distinguishes the type of data frame,
It includes the data to be transmitted and Fe2, which is a checksum of the entire transmission frame.

Note that the token frames are transmitted over the network in a predetermined order.

Transmission in the data transmission device 2-i is started by receiving a token frame in the reception control unit i-1 in FIG. 2, and issuing a transmission instruction from the control unit i-2 to the transmission control unit i-3, The transmission control unit f-3 performs this by sending the frame sent from the control unit i-2 to the transmission path 1.

On the other hand, reception at the data transmission device 2-j is performed through the transmission path 1.
The reception control unit j-1 always receives frames transmitted over the top, and if the frame is addressed to the own station, the control unit j-1
This is done by sending the frame to No. 2 and discarding the frame if it is not addressed to the local station.

Further, if frames are simultaneously transmitted from another data transmission device on the transmission path 1 during transmission by the data transmission device 2-i and a collision occurs, the collision detection unit i-4 controls the control unit i- 2 is notified that a collision has been detected.

When the data transmission device 2-i transmits a normal data frame, it starts by receiving a token frame addressed to itself. When receiving a token frame addressed to itself and obtaining transmission rights, the data transmission device 2-
A data frame including the address of the data transmission device 2-i, the address of the own data transmission device 2-i, frame identification information indicating the data frame, the data to be transmitted, and the checksum Fe2 is transmitted to the transmission line 1''.

Note that all data transmission devices on transmission line 1 are always
It receives frames on transmission path 1, and discards them if they are not addressed to itself.

Therefore, when the destination data transmission device 2-j receives the data frame addressed to itself, it transmits the data frame to the source data transmission device 2-j.
- In order to notify i that the data frame has been received, the sender's address in the data frame is extracted and a response frame is constructed, and the sender's data transmission device 2
- Send the response frame to i.

Upon receiving the response frame from the destination data transmission device 2-j, the source data transmission device 2-i completes the transmission and transmits the next data in a predetermined order in order to relinquish the transmission right. Send a token frame to the transmission device.

Next, a case where the data transmission device 2-i of this embodiment performs emergency communication will be described.

First, when the data transmission device 2-i that performs emergency communication has already received a token frame, it performs emergency communication using a normal transmission operation.

Further, when the data transmission device 2-i that performs emergency communication has not yet received the token frame and the data transmission device 2-j has received the token frame, the data transmission device 2-j When receiving the token frame addressed to itself, the data transmission device 2-i transmits the addressed data frame to the data transmission device 2-i.
When the data frame transmitted above starts to be received, the frame is forcibly transmitted onto the transmission path 1, causing a collision.

Therefore, by detecting the collision, the data transmission device 2-j
Stop sending when you know there is an emergency message.

On the other hand, the data transmission device 2-i confirms that there are no more data frames to be transmitted on the transmission path 1, and transmits an emergency communication data frame to the data transmission device 2-h. -h receives the data frame of this emergency communication and returns a response frame indicating that it has been received to the data transmission device 2-i, so the data transmission device 2-i receives the response frame and transmits the emergency communication. complete.

Then, the data transmission device 2-i sends a message to a predetermined data transmission device in order to give up the transmission right.
l--Send a frame.

〔Effect of the invention〕

As explained above, the communication method of the local network system of the present invention forcibly transmits a frame when there is a frame being transmitted on the transmission path and causes a collision, thereby interrupting other transmissions. This has the effect that emergency communications can be made immediately without receiving a token frame.

■...Transmission line, 2-1.2-2. ~2-1. ~
2-j, ~2-N...Data transmission device, j-1
......Reception control unit, i-2...Control unit,
i-3...Transmission control unit, i-4...Collision detection unit.

Claims (1)

[Claims] 1. A transmission path on a bus and a plurality of data transmission devices connected to the transmission path, each of the data transmission devices transmitting frames of data to each other via the transmission path. In a communication method of a token bus type local network system that has a function of transmitting data in units of units and detecting data collisions due to simultaneous transmission, one of the data transmission devices transmits frames on the transmission path. when the data transmission device is transmitting a new frame and causing a collision with the frame already being transmitted, thereby interrupting the transmission of the other data transmission device and performing its own emergency communication; A communication method for a local network system characterized by transmitting a token frame and relinquishing transmission rights after the emergency communication is completed. 2. A transmission path on a bus and a plurality of data transmission devices connected to the transmission path, and each of these data transmission devices:
In a communication method of a token bus type local network system that has a function of mutually transmitting data in frame units via the transmission path and detecting data collisions due to simultaneous transmission, (A) emergency communication. When the first data transmission device that transmits the token frame has not received the token frame, the frame of the second data transmission device that has received the token frame is forcibly transmitted to the transmission path, and a new frame is forcibly transmitted. (B) upon detecting the collision, the second data transmission device interrupts its own transmission; and (C) detects the interruption of the transmission. (D) After the emergency communication is completed, the first data transmission device transmits a token frame and relinquishes the transmission right. Communication method of local network system featuring characteristics.