JP3050666B2 - Synchronization method in multiplex transmission system - 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 synchronization system in a multiplex transmission system using a transmission system.

[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, as shown in FIG. 3 (b), terminates the use state of the multiplex transmission line (multiplex bus) composed of twisted pair lines and the like, and confirms the idle (idle) state of a certain length or more.
Data transmission for each frame is started in the idle state. Then, the transmission waveform of the own station and the waveform on the multiplexed bus are compared bit by bit. If they do not match, it is determined that there is a signal collision, the 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. As shown in FIG. 3A, the message format of the frame usually includes a start of message (SOM) indicating the start of a message, a data ID indicating the content of data that follows, a data area of a predetermined length, Error check code such as CRC, ACK signal area for returning acknowledgment signal (ACK signal) from all multiplex nodes in bit correspondence, EOM (End Of Message) indicating end of data In the transmission system, a digital transmission system in which an inversion code, that is, a so-called stuff bit, is always inserted by one bit when the same code continues for a predetermined bit in the frame data has been used.

Therefore, the receiving multiplex node first detects the rising edge of the SOM of the message transmitted on the multiplexing bus, synchronizes the frame at the rising edge, and then resynchronizes the bit at the rising edge of the data.

[0006]

However, in the above transmission method, the SOM of the message is, as shown in FIG.
This is a 6-bit dominant special code. If the SOM is followed by a dominant code, the time required for re-synchronization increases, and the bit length of the reference clock differs between multiple nodes. In the case where there is a tolerance due to the above, there is a problem that bit synchronization is lost due to the accumulation of the clock speed difference and a bit error occurs.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a multiplex transmission system capable of reliably achieving bit synchronization without depending on variations in reference clocks of each multiplex node. I do.

[0008]

According to the present invention, when transmitting data for each frame from a transmission multiplex node to a multiplex transmission line, the transmission multiplex node sets an idle state of the multiplex transmission line. When the idle state reaches a predetermined time, a frame having a start code is transmitted to the multiplex transmission path, and the receiving multiplex node detects the start code and synchronizes with the multiplex transmission method, The start code adds a special bit pattern to the end, and the receiving multiplex node detects the special code and provides a multiplex transmission scheme for re-establishing synchronization.

[0009]

A special bit pattern is added to the end of the start code of a frame transmitted to the multiplex transmission path, and synchronization is restored at the rise of the bit pattern. Therefore, even if the same code as the above-mentioned start code follows the start code, the time for re-synchronization is shortened, and synchronization can be reliably prevented by preventing a synchronization shift.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In the multiplex transmission method according to the present invention, a digital transmission method is used in which a NRZ (Non Return to Zero) code is used as a transmission code, a stuff bit is inserted into the NRZ code, and synchronization is achieved by the stuff bit.

[0011] The message frame according to the present invention is an SOM.
The configuration is the same as that shown in FIG. 3A except for the area of (frame start code). Therefore, FIG. 1 shows a configuration diagram of one embodiment of the SOM according to the present invention. In FIG. 1, the SOM is provided with a special code a consisting of a 6-bit dominant breaking the stuff bit rule, followed by a special bit pattern b consisting of a 1-bit passive (passive) and a dominant. The bit pattern b is SO
Even if the same code as the special code a of the SOM follows the M, each multiplex node is re-synchronized at the rising edge of the bit pattern b so as to prevent the synchronization shift.

In this embodiment, the transmitting side always inserts one bit of an inverted code when the same code continues for 5 bits in the frame data, and the receiving side removes the inserted bits in the reverse procedure. Therefore, no passive data of 6 bits or more appears in the frame data on the multiplex bus, 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 based on the configuration diagram of the transmission system in FIG.
Here, it is assumed that the multiplex nodes 10, 20, and 30 are connected to a common multiplex bus MB, and that messages are transmitted between the multiplex nodes 10, 20, and 30. When the passive state of 6 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, 30.
Can start transmitting a message when it detects a 6-bit passive on the multiplexed bus.

In FIG. 2, the multiplex node 10 is a transmitting node, and the multiplex nodes 20 and 30 are receiving nodes. Upon detecting the idle state of the multiplex bus MB, the transmitting-side multiplex node 10 starts transmitting a message, and transmits the SOM including the special code a and the special bit pattern b to the multiplex bus M.
B. The receiving-side multiplex nodes 20 and 30 detect the rising of the special code a from the transmitting-side multiplex node 10, synchronize the frames with the rising edge, and detect the rising of the special bit pattern b composed of passive and dominant. Then, bit synchronization is established at the rising edge, and the following frame data is fetched.

Therefore, in this embodiment, the SOM of the message
Is composed of a special code and a special bit pattern, and synchronization is re-established at the rising edge of the special bit pattern.Thus, even if the same code as the special code of the SOM follows the SOM, synchronization can be ensured. Synchronization deviation due to a clock tolerance or the like and a bit error accompanying the deviation can be prevented.

[0015]

As described above, according to the present invention, when transmitting data for each frame from a transmission multiplex node to a multiplex transmission line, the transmission multiplex node detects an idle state of the multiplex transmission line and When the state reaches the predetermined time,
Transmitting a frame having a start code to the multiplex transmission path,
In a multiplexing transmission system in which a receiving multiplex node detects the start code and performs synchronization, the start code adds a special bit pattern to the end, and the receiving multiplex node detects the special code and synchronizes. Because it is taken again, without depending on the variation of the reference clock of each multiplex node,
Bit synchronization can be ensured, which can increase the reliability of multiplex transmission.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a configuration of a message frame and waveforms on a multiplex bus.

[Explanation of symbols]

 10, 20, 30 Multi-node MB Multi-transmission line (multi-bus) A, B Message a Special code b Special bit pattern

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Matsuda 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Hiroaki Sakamoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Matsu Inside (72) Inventor Yoshikazu Shinnobu 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Corporation (72) Hideki Nakazono 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda In-company (56) References JP-A-61-251251 (JP, A) JP-A-2-250449 (JP, A) JP-A-5-110571 (JP, A) (58) Fields investigated (Int. . ^7, DB name) H04L 12/40 H04L 12/44 H04L 12/46

Claims (2)

(57) [Claims] 1. When transmitting data for each frame from a transmission multiplex node to a multiplex transmission line, the transmission multiplex node detects an idle state of the multiplex transmission line, and when the idle state reaches a predetermined time, the multiplex node transmits the multiplexed data. The transmission multiplex node transmits a frame having a start code to the transmission path, and the receiving multiplex node detects the start code and synchronizes the multiplex transmission method in the multiplex transmission system, in which the start code adds a special bit pattern to the end thereof, and A synchronization method in a multiplex transmission method, wherein the multiplex node detects the bit pattern and resynchronizes. 2. The synchronous system according to claim 1, wherein said special bit pattern is composed of passive and dominant codes.