JP3050665B2 - Multiplex transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a so-called non-destructive mediation type.
CSMA / CD (Carrier Sense Multiple Access / Collision De
tection) The present invention relates to a multiplex transmission method using a transmission method.

[0002]

2. Description of the Related Art In recent years, with the rapid development of car electronics, problems such as an increase in units and an enlargement of harnesses have arisen. Solving the problems of these transmission systems,
Distributed control type LAN (Local Area Network) as a highly reliable and versatile automotive multiplex transmission system
Have been proposed. Above all, open systems (for example, there is no need to change other nodes even if nodes are added or deleted due to grade differences, destinations, etc. in the same model), non-destructive that meets responsiveness and versatility requirements Arbitration-type CSMA / CD has attracted attention and is widely used.

[0003] In this non-destructive arbitration type CSMA / CD transmission system,
Each multiplex node checks the idle (idle) state of the multiplex transmission path, and starts data transmission for each frame in the idle state. Then, the transmission waveform of the own station is compared with the waveform on the multiplex transmission path (multiplex bus) for each bit, and if they do not match, it is determined that there is a signal collision, transmission is stopped, and the process returns to the confirmation of the idle state. . In addition, a multiplex node transmitting a signal having a high priority has the same waveform on a multiplex bus as its own signal, and thus continues transmission without detecting a collision.

In the nondestructive arbitration type CSMA / CD transmission system, since the transmission distance, which is a characteristic of an automobile, is short, and the transmission speed is relatively low, each multiplex node can simultaneously observe signals on a multiplex bus. It is excellent in that it has a high use efficiency and does not require complicated control procedures such as random back-off. Next, FIG. 4 shows an operation example of the non-destructive arbitration type CSMA / CD system when a plurality of multiplex nodes are connected via a multiplex bus composed of twisted pair wires or the like. FIG.
This shows a case where transmission of a high-priority message A (see FIG. 4 (a)) and a low-priority message B (see FIG. 4 (a)) compete on a multiplex bus. The transmission can be performed in the order of the messages (see FIG. 4 (c)).

[0005]

However, in an actual system, as shown in FIG. 5, due to the difference in the bit length of the reference clock caused by variations in the elements of the clock generation source, for example, a multiplex node having a slow reference clock generation is used. When a high-priority message A and a low-priority message B from a multiplex node generating a reference clock are waiting for transmission, the message A after the use of the multiplex bus shown in FIG. As shown in FIGS. 5B and 5C, when the confirmation time of the idle state of the message B is Ta and Tb, a time difference Tc occurs due to the speed difference of the reference clock.
Here, when the message B enters the transmission state, the transmission of the message A is stopped by the carrier detection function despite the high priority. In other words, there is a problem that priorities are ignored due to variations in the bit length of the reference clock of each multiplex node.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and performs priority control in accordance with the priority of a message reliably and at low cost without depending on the variation of the reference clock of each multiplex node. It is an object of the present invention to provide a multiplex transmission method that can perform the multiplex transmission.

[0007]

In order to solve the above-mentioned object, according to the present invention, there are provided a plurality of multiplex nodes connected to each other via a common multiplex transmission line. When transmitting data for each frame to a channel, an idle state of the multiplex transmission path is detected, and when the idle state reaches a predetermined time, transmission is permitted for the frame to be transmitted in a multiplex transmission scheme for transmitting the frame. A multiplex transmission method is provided in which a signal is added and transmitted to the multiplex transmission path, and when each multiplex node detects the transmission permission signal, the multiplex transmission system enters a state in which a frame can be transmitted.

[0008]

A transmission permission signal is provided after the end of all frames transmitted to the multiplex transmission path, and the multiplex node waiting for transmission detects the transmission permission signal or the idle state of the transmission path and starts transmitting a frame. Therefore, even if there are variations in the reference clocks between competing multiplex nodes, priority control can be reliably performed according to the priority of the message.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram showing an embodiment of a frame format of a message used in the multiplex transmission system according to the present invention. In FIG. 1, the message includes a transmission start code indicating the start of transmission, a data area for storing data, and a transmission end code indicating the end of transmission.

In the embodiment, the transmission start code is composed of a 6-bit dominant, a 1-bit passive, a dominant, and a passive. The transmission end code is a 1-bit passive for preventing a synchronization shift when codes are consecutive in the data area, a dominant synchronization unit a, a 6-bit passive indicating the end of a message, and a 1-bit each indicating a transmission permission. The bit pattern is a special pattern that does not occur in the message.

In this embodiment, the data format is NRZ (No.
n Return to Zero) method, the transmitting side always inserts one bit of an inverted code when the same code continues for five bits in the frame data, and the receiving side removes the inserted bits in the reverse procedure. Therefore, the frame data on the multiplex bus contains 6
No more than bits of passive appear, and the end of the message can be easily determined.

Next, the operation of the multiplex transmission system according to the present invention will be described with reference to the configuration diagram of the transmission system of FIG. 2 and the waveform diagram of FIG. Here, as shown in FIG.
It is assumed that the multiplex nodes 10, 20, and 30 are connected to a common multiplex bus MB.
It is assumed that a message is transmitted between 0. Further, when a passive state of 8 bits or more continues on the multiplex bus MB, it means that the multiplex bus MB is in an idle state, and each of the multiplex nodes 10, 20, and 30 places 8 bits on the multiplex bus. Message transmission can be started when the passive is detected.

In FIG. 3, there are a multiplex node 10 which is already transmitting a message (see FIG. 3 (a)) on a multipath bus MB, and multiplex nodes 20 and 30 which are waiting for transmission.
Reference numerals 0 and 30 denote the transmission end code synchronization unit a of the transmission-side multiplex node 10 to prevent the reference clock from being out of synchronization, and then synchronize at the rising edge of the transmission permission signal b to detect the transmission permission signal b. At the same time, transmission of a message (see FIGS. 3B and 3C) is started.

If the message of the multiplex node 30 has a higher priority than the message of the multiplex node 20, the transmission waveform of the multiplex node 20 and the waveform on the multiplex bus MB (FIG. 3D) ), The multiplex node 20 determines that a signal collision has occurred by the carrier detection function, and stops transmitting the message. As a result, only the message of the multiplex node 30 exists on the multiplex bus MB.

Therefore, in this embodiment, a transmission end code including a special bit pattern which does not occur in the message is added to the end of the message to synchronize the competing multiplex nodes immediately before the start of frame transmission (2 (Before a bit), it is not necessary to adjust clock time variations caused by variations in the elements of the clock generation source of each multiplex node, and the frame can be transmitted in accordance with the priority.

[0016]

As described above, according to the present invention, a plurality of multiplex nodes are connected to each other via a common multiplex transmission line, and data for each frame is transmitted from any of the multiplex nodes to the multiplex transmission line. When transmitting, the idle state of the multiplex transmission path is detected, and when the idle state reaches a predetermined time, in a multiplex transmission system for transmitting the frame, a transmission permission signal is added to the frame to be transmitted, After transmitting to the multiplex transmission path and each multiplex node detects the transmission permission signal, the multiplex node becomes ready to transmit the frame. Therefore, the multiplex node does not depend on the variation of the reference clock of each multiplex node, but according to the priority of the message. Priority control can be performed reliably and at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a frame format of a message used in a multiplex transmission system according to the present invention.

FIG. 2 is a system configuration diagram for explaining the operation of the multiplex transmission system according to the present invention.

FIG. 3 is a waveform chart for explaining the operation of the multiplex transmission system according to the present invention.

FIG. 4 is a waveform chart for explaining the operation of the nondestructive arbitration type CSMA / CD system.

FIG. 5 is a configuration diagram showing a schematic configuration of an automobile multiplex transmission system using the CSMA / CD system.

[Explanation of symbols]

 10, 20, 30 multiplex node MB multiplex transmission path (multiplex bus) A, B message a synchronization unit b transmission permission signal

──────────────────────────────────────────────────続 き Continuing from the front page (72) Kyosuke Hashimoto, Inventor Furukawa Electric Co., Ltd. 2-6-1 Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Yoshikazu Shintoki 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture No. Mazda Co., Ltd. (72) Inventor Hiroaki Sakamoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (72) Koji Terayama 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda shares In-company (56) References JP-A-63-94733 (JP, A) JP-A-5-3478 (JP, A) JP-A-2-121543 (JP, A) JP-A-2-121544 (JP, A) JP-A-2-250449 (JP, A) JP-A-5-110575 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/40 H04L 12/44 H04L 12 / 46

Claims (2)

(57) [Claims] 1. A multiplex transmission path comprising: a plurality of multiplex nodes connected to each other via a common multiplex transmission path, wherein when transmitting data for each frame from any one of the multiplex nodes to the multiplex transmission path, When the idle state reaches a predetermined time, in a multiplex transmission system for transmitting the frame, a transmission permission signal is added to the frame to be transmitted, and the frame is transmitted to the multiplex transmission path. The present invention provides a multiplex transmission system in which a frame transmission is enabled when the transmission permission signal is detected. 2. The transmission permission signal according to claim 1, wherein the transmission permission signal has a bit pattern that cannot occur in a frame.
The multiplex transmission method described.