JPH04284750A - Multiplex transmission system - Google Patents

Abstract

PURPOSE:To implement information interrupt with high priority and to detect the information by providing an interrupt function to a multiplex node requiring the information interrupt. CONSTITUTION:Plural multiplex nodes send information via buses +24, -25. Suppose that a transmission request with high priority takes place during the transmission while monopolizing the buses +24, -25. A multiplex node implementing a transmission request closes a relay 26 to short-circuit forcibly the buses +24, -25 thereby causing disabled communication and interrupting the information transmission. Furthermore, when a transmission request comes from other multiplex node, the request is reserved, the relay 26 is opened to release the communication disable state thereby sending the information with high priority.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to CSMA (Carri
er Sense Multiple Access
) transmission method.

0002

[Prior Art] Conventionally, in this type of transmission system, CSMA
/CD (Carrier Sense Multipl
e Access / Collision Dete
A distributed control type multiplex transmission system using a transmission system has been proposed. As shown in FIG. 4, this CSMA/CD transmission method uses a multiplex transmission path (hereinafter referred to as "multiple bus") consisting of, for example, twisted pair cables, etc.
A plurality of multiple nodes N1 to N5 interconnected via
Each of the multiplex nodes N1 to N5 monitors the transmission status of the multiplex bus MB in advance, and when a transmission request occurs, the transmitting multiplex node that generated the transmission request waits until the multiplex bus MB becomes unused. Then, data is transmitted to the multiplex bus MB, and data is also received during the transmission. If a collision of signals on the multiplex bus MB is detected, that is, while the transmitting multiplex node is transmitting a signal that does not monopolize the multiplex bus MB, another multiplex node may transmit data and monopolize the multiplex bus MB. If the transmitting multiplex node detects that the transmitting multiplex node is in a state where the multiplex bus MB is in an unused state, it suspends its own transmission, waits until the multiplex bus MB becomes unused again, and then retransmits.

Furthermore, as shown in FIG. 5, a connection circuit for connecting the multiplex nodes N1 to N5 to the multiplex bus MB has also been proposed. In FIG. 5, the connection terminals of each multiple node are the switching elements 12, 13 of the connection circuit and the protective resistors 18, 1 of the switching elements 12, 13, respectively.
9 to bus +24 and bus -25, which constitute multiple bus MB. Further, the bus +24 and the bus -25 are respectively connected to the input terminals of the comparator 11, and the output terminal of the comparator 11 is connected to the receiving terminal of the multiple node. In addition, 14 and 15 are constant current circuits that flow a constant current to bus +24 and bus -25, and 16
, 17 are protection diodes, 20 and 21 are bias resistors,
22 and 23 indicate termination circuits.

In the above connection circuit, when the multiplex node outputs a high level to the transmission terminal as data transmission, both switching elements 12 and 13 are turned on, and the bus +24 is turned on.
The potential of becomes higher than the potential of the bus -25, thereby making the multiplex bus MB exclusive, and the same high level as the transmitting terminal is also input to the output of the comparator 11, that is, the receiving terminal of the multiplex node. On the other hand, if the multiplex node outputs a low level for data transmission or the multiplex bus MB is in an unused state, the switching elements 12 and 1
3 are both off, and the potential of bus +24 is bus -25.
, and the multiplexed bus MB becomes non-exclusive. As a result, a low level is input to the output of the comparator 11, that is, the receiving terminal of the multiple node.

As mentioned above, even while transmitting a signal, the transmitting multiplex node inputs the signal on the multiplex bus MB to the comparator 11.
are being received via. When the above-mentioned transmitting multiplex node detects a high level at the receiving terminal while outputting a low level as a transmitter, the multiplexed bus MB is in a state where the multiplexed bus MB is exclusively used for transmission by other multiplexed nodes, and the signal is transmitted on the multiplexed bus MB. It is determined that there is a collision and communication is not possible, and the transmission is stopped.
Retransmission was performed after waiting until the multiplex bus MB became unused again.

[0006] In such a multiplex transmission system, in order to transmit a highly urgent signal preferentially over other signals, a special signal to be transmitted in an emergency is set in advance on the multiplex bus MB. The multiplex node that generated the signal outputs the emergency signal for a predetermined period on the multiplex bus MB, and the transmitting multiplex node detects the emergency signal and outputs the data to be transmitted after stopping the transmission. -20
There is a transmission interrupt method shown in Japanese Patent No. 8738.

[0007]

[Problem to be Solved by the Invention] However, in the above method, if an emergency signal occurs during transmission, the transmitting multiplex node must detect the emergency signal. An electronic circuit and an interrupt execution program for the central processing unit (hereinafter referred to as "CPU") are required to implement the interrupt function in the communication control circuit, making the configuration of each multi-node complex and increasing the manufacturing cost. There was a problem with that.

The present invention has been made in view of the above problems, and makes it possible to interrupt high-priority data and detect the interrupt by simply adding an interrupt function to multiple nodes that require data interrupts. The purpose is to provide a multiplex transmission system that can

[0009]

[Means for Solving the Problems] In order to solve the above object, the present invention has a plurality of nodes mutually connected via at least two common transmission paths, and each node is connected to the transmission path. multiplex transmission that constantly monitors the state of the transmission path, recognizes that the transmission path is in exclusive use, and transmits data via the transmission path when the transmission path becomes unused. In this method, when a sending node is transmitting a signal that exclusively uses the transmission path, and a request to send data with a higher priority than the data being sent occurs, the node making the transmission request uses each of the transmission paths. Forcibly puts the node in a communication disabled state, interrupts data transmission, and if there is a transmission request from another node, suspends the request, then releases the communication disabled state and transmits the high priority data. A multiplex transmission scheme for transmission is provided.

0010

[Operation] When a request to send high-priority data occurs,
After forcing each transmission path into a communication disabled state and interrupting data transmission, the communication disabled state is released and data transmission is performed. Therefore, by using the interrupt function added only to necessary multiple nodes, it is possible to transmit high priority data while other data is being transmitted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing a multiplex node N and a multiplex bus MB used in a multiplex transmission system according to the present invention. It can be used for LAN (Local Area Network). Further, FIG. 2 is a diagram showing an example of a message format of a frame transmitted over the network.

In FIG. 1, an input circuit 3 of a multiple node N
0 takes in various signals such as detection signals detected by various sensors in the vehicle and on/off signals of switches, and supplies the various signals taken in to the CPU 31. The CPU 31 is
When the multiplex node N is a transmitting multiplex node, the various input signals mentioned above are processed as necessary, and the signals that need to be transmitted are converted into data area information (D) in the frame shown in FIG.
ATA1 to DATA4), and the communication control circuit 32
supply to. In addition, when the multiplex node N is a receiving multiplex node, the CPU 31 determines whether the frame transferred from the communication control circuit 32 includes data necessary for the local station, and determines whether the frame's ID code (see FIG. 2) The received frame is selected based on the bit value of the ID code. Then, the necessary data DATA1~
DATA4 (see FIG. 2) is calculated based on the above value and is output to the output circuit 33.

When the multiplex node N is a transmitting multiplex node, the communication control circuit 32 generates and adds an error check code such as a CRC (cyclic code) to the information in the data area to be input, and then outputs the final information. Generate a frame (Figure 2
) and based on CSMA/CD control, the final frame is encoded as necessary and sent to the multiplex bus MB. Furthermore, if the multiplex node N is a receiving multiplex node,
The communication control circuit 32 receives the frame sent to the multiplex bus MB, encodes the frame as necessary, and further checks the received data based on an error check code, and if there is no error, the data is processed. CPU3
Transfer to 1.

When the output circuit 33 receives data from the CPU 31, it outputs the data to various devices in the vehicle connected to its own station. In addition, in FIG. 2, SO
M is an area indicating the start of a message, PRI is an area that determines the priority order when multiple multiplex nodes simultaneously send data to multiplex bus MB, CONT is a control data area containing data indicating data length, and EOD
is an area indicating the end of data, an ACK signal area is an area for returning ACK signals from all multiple nodes, and EO
M is an area indicating the end of the message.

FIG. 3 is a diagram showing a connection circuit according to the present invention. Note that, for convenience of explanation, the same components as those in FIG. 5 are given the same reference numerals and the explanation will be omitted. 3 is different from FIG. 5 in that an emergency signal request relay 26 is provided between the protective resistors 18 and 19 and the multiplex bus MB to short-circuit bus +24 and bus -25. , on/off control is performed by an emergency signal input from the CPU 31 via a control terminal. That is, when the relay 26 is turned on by the emergency signal, the bus +24 and the bus -25 are short-circuited and have the same potential, making it impossible for all multiplex nodes connected to the multiplex bus MB to transmit signals. The entire network becomes unable to communicate. The emergency signal request relay 26 may be added only to multiple nodes that require emergency data interruption.

That is, the present invention makes use of the failure mode of the multiplex transmission system, and when an urgent data transmission request occurs to a predetermined multiple node having an interrupt function, multiple nodes other than the multiple node concerned Multiple bus MB
When the multi-node is monopolizing the bus, the multi-node short-circuits the bus +24 and bus-25 by turning on the contact of the emergency signal request relay 26 between the bus +24 and the bus-25 within the node. Force the network system to become unable to communicate. When the system becomes unable to communicate,
A multiplex node that is transmitting data by exclusively using the multiplex bus MB detects communication failure due to its own failure mode and interrupts data transmission.

[0017] In this state, the multi-node that has received a request to transmit emergency data must open the contact of its own emergency signal request relay 26 to release the communication-disabled state and immediately continue transmitting emergency data. Can be done. Furthermore, other multiplex nodes, including the multiplex node that was transmitting earlier, cannot transmit data while the emergency data is being transmitted, unless a request for emergency data that takes priority over the emergency data occurs.

Therefore, in this embodiment, a relay for requesting an emergency signal having a simple configuration is provided in a multiplex node, and when a request for transmitting emergency data occurs, the contacts of the relay are connected to connect two multiplex buses. After forcibly short-circuiting the system and making the system unable to communicate, the contact of the above relay is opened to release the communication disabled state and continue to transmit emergency data.
Even if other multiple nodes are transmitting data, it is possible to interrupt the urgent data and send the urgent data preferentially, and it also prevents the configuration of multiple nodes from becoming complicated and reduces production costs. It is possible to reduce the

[0019]

As explained above, the present invention has a plurality of nodes interconnected via at least two common transmission paths, and each node constantly monitors the state of the transmission path. When the transmitting node recognizes that it is monopolizing the transmission path and the transmission path becomes unused, the transmitting node transmits data via the transmission path. When a request to send data with a higher priority than the data being sent occurs while a node is transmitting a signal that exclusively uses the transmission path, the node making the transmission request forcibly uses each transmission path to communicate. The communication disabled state is set to interrupt data transmission, and if there is a transmission request from another node, the request is put on hold, and then the communication disabled state is released and the high priority data is transmitted.
Interruption of high-priority data and detection of that interruption becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing multiple nodes and multiple buses used in a multiplex transmission system according to the present invention.

FIG. 2 is a diagram showing an example of a message format of a frame used in the present invention.

FIG. 3 is a diagram showing a connection circuit according to the invention.

FIG. 4 is a system configuration diagram of a multiplex transmission method using the CSMA/CD transmission method.

FIG. 5 is a diagram showing a conventional connection circuit.

[Explanation of symbols]

N, N1 to N5 multiple nodes MB multiplex bus 26 Emergency signal request relay 30 Input circuit 31 CPU 32 Communication control circuit 33 Output circuit

Claims (2)

[Claims] Claim 1: A plurality of nodes are interconnected via at least two common transmission paths, each node constantly monitors the status of the transmission path, and a sending node exclusively uses the transmission path. When the transmission path becomes unused, the transmitting node transmits a signal to exclusively use the transmission path in a multiplex transmission method that transmits data via the transmission path. During the process, when a request to send data with a higher priority than the data being sent occurs, the node making the request forcibly puts each transmission path into a communication disabled state and interrupts data transmission, Furthermore, if there is a transmission request from another node, the request is put on hold, the communication disabled state is canceled, and the high priority data is transmitted. 2. The multiplex transmission system according to claim 1, wherein the node making the transmission request short-circuits each of the transmission lines to forcibly disable communication on each of the transmission lines.