JPH0646732B2 - Multiple communication system of single communication line - Google Patents

Description

TECHNICAL FIELD The present invention relates to a single communication line multiplex communication system suitable for use in, for example, exchanging signals between a plurality of devices mounted on a vehicle. .

"Prior Art" It is desirable that a transmitting system or a receiving system mounted on a vehicle has a simple structure and is lightweight. Therefore, conventionally, one that connects two nodes with one communication line (optical fiber, coaxial cable, etc.), one that connects multiple nodes with one communication line and one synchronization signal line,
In addition, a system for connecting a plurality of nodes with one communication line and one or more address lines has been developed to simplify the configuration.

[Problems to be Solved by the Invention] However, it cannot be said that the usage efficiency of the signal line in the conventional system is still sufficient, and the simplification is still a step away from the viewpoint of the configuration.

The present invention has been made in view of the above circumstances, and it is possible to perform transmission and reception between a plurality of nodes with only one communication line, which improves the utilization efficiency of the communication line and greatly simplifies the configuration. It is an object of the present invention to provide a multiplex communication system of a single communication line capable of achieving the above.

[Means for Solving Problems] In order to solve the above problems, the present invention connects input / output terminals of a plurality of nodes having digital signal transmission / reception functions with one communication line, and The node has a unique node address that does not overlap, the transmitting node sends its node address and the partner node address as node data, and the receiving node receives the data on the communication line as its own node. In a transmission / reception system configured to read this data only when it includes an address, the communication line is configured such that one of high and low levels has priority, and one bit of data is divided into the first half / second half period, It is assumed that the signal level in the first half period indicates the bit, while the signal level in the second half period is the inverted signal level in the first half period. The node which sets and transmits the data to the communication line or receives the data from the communication line, and the node which performs the transmission sequentially monitors the signal level on the communication line bit by bit and compares it with the transmitted data. , If the signal level corresponding to the transmitted data is the non-priority level, but the signal level on the communication line is the priority level, it is determined that there is data collision, and data collision is determined. The node stops the transmission operation and performs the transmission operation again when the signal level on the communication line becomes the non-priority level for a period corresponding to 1.5 bits of the data or more.

"Operation" Each of the nodes performing the transmission operation, although the signal level corresponding to the transmission data is the non-priority level,
When the signal level on the communication line is the priority level, it is determined that the data collide. Since the node that makes this determination stops the transmission operation, eventually, the node that outputs the bit corresponding to the priority level more continuously is alternatively selected, and only this node continues the transmission operation.

In addition, the node that has stopped the transmission operation detects that the communication line is in an idle state when the signal level on the communication line becomes the non-priority level for a period corresponding to 1.5 bits of data or more, and the transmission operation is performed. Since it is performed again, it is possible to reduce the idle period of the communication line and improve the utilization efficiency of the communication line.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an embodiment when the present invention is applied to a vehicle transmission / reception system for a motorcycle.
The transmission / reception system shown in the figure has a radio unit (node) 1 mounted on a vehicle, an air suspension unit (node) 2 capable of adjusting a vehicle height, and a radio switch unit (node) for a driver to arbitrarily control these units. Three
And air suspension switch unit (node) 4
And a radio switch unit (node) 5 for a passenger to control the radio unit 1, and a display unit (node) 6 for displaying operating states of both the radio unit 1 and the air suspension unit 2, respectively. Has been done. Input / output terminals 1a of the units 1 to 6
6a are respectively connected to one data line (harness) 10, and all signals are transmitted and received between the units 1 to 6 via only the data line 10. The above system can be regarded as a form of LAN (Local Area Network) for mutual data communication.

The units 1 to 6 are microcomputers 1b to, respectively.
6b. As shown in FIG. 2, the output terminal 1c of the microcomputer 1b is connected to a transistor Tr via a resistor.
Of the transistor Tr, the collector of the transistor Tr is connected to the data line 10 via the input / output terminal 1a of the unit 1, and the positive power source (voltage Vcc) via the resistor.
It is connected to the. The input terminal 1d of the microcomputer 1b is connected to the collector of the transistor Tr, and the emitter of the transistor Tr is grounded. The units 2 to 6 have the same configuration as the unit 1.

Next, the characteristics of the data line 10 will be described.

First, the output terminals 1c of the microcomputers 1b to 6b
Any one signal level from 6c is high level (H)
At the time, since the data line 10 is grounded through any one of the transistors Tr, the signal level on the data line 10 becomes a low level (L). When all the signal levels from the output terminals 1c to 6c are low level (L), the signal level on the data line 10 becomes high level (H). That is, in the data line 10, the low level (L) side is prioritized, and the units 1 to 6 are
If any of the input / output terminals 1a to 6a becomes low level,
The data line 10 is forced to the low level regardless of the level of the other input / output terminals.

Next, the data signal transmitted from the units 1 to 6 on the data line 10 will be described. This signal is start-stop synchronization type and is as shown in FIG. That is, the low level start signal (STR (L)) of 5.5 bit (STR
1), 0.5 of high level start bit (S (H))
bit, the start bit gap (G (L)) of 0.
5 bits, 8 bits of the data part, 0. of parity (P (H)).
5 bits, a parity gap (G (L)) of 0.5 bits and an end signal (END (H)) of 1 bit (total of 16.5 bits). In the data part, the first 0.5 bit is the data D and the remaining 0.5 bit is the gap G for every 1 bit, and the data D is at a high level (hereinafter referred to as H).
The gap G is set to L when, and the gap G is set to H when the data D is at a low level (hereinafter referred to as L). In this way, the gap G is provided for each bit of the data signal so that the usage state of the data line 10 and the collision of the data signals on the data line 10 can be detected immediately as described later. This is because. When a second, third or more data signal follows this data signal, the start signal (STR (L)) of these data signals is 1 bit (STR2) and the entire data signal is 12 bits.

Therefore, when a signal is being sent out on the data line 10 (when the data line 10 is in use), the signal level H on the line 10 is always 1 bit or less.
Therefore, the signal level H on the data line 10 is 1.5.
It is possible to detect whether the data line 10 is unused or not by detecting whether it is equal to or more than 1 bit. A receiving unit address and a transmitting unit address are stored in the data portion of the first data signal.

Two types of transmission methods are used for transmitting the data signal as described below. Among the units 1 to 6, the radio unit 1 and the air suspension unit 2 which have a large data processing amount are other units (slave units) 3
It is a master unit that manages the transmission of ~ 6. The data signal is transmitted from the master unit 1, 2 to the slave unit (display unit) 6 in the data format shown in FIG.
The third, third data signals D ₁ , D ₂ , D ₃ , ... Are unilaterally transmitted as shown in FIG. 1 (hereinafter, transmission by this transmission method is referred to as "asynchronous transmission"). Also, from slave units (switch units) 3 to 5 to master unit 1,
The data signal is transmitted to the slave unit 2 in the data format shown in FIGS. 4 (b) and 4 (c). As shown in FIG.
To any one of the units 4 and 5, the first in Fig. 4 (b)
Data signal is sent. After that, the receiving unit 3
Or 4 or 5 to the transmission source unit 1 or 2 designated by the transmission unit address of the first data signal, the respective data signals D ₁ , ₁ , 2, 3 ... Of FIG.
D _2, D _3, and transmits the ... (hereinafter the transmission by the transmission method called "synchronous transmission"). Thus, the master unit 1 or 2 manages the signal transmission of the slave units 3 to 5. More specifically, slave units 3 and 5
Is managed by the master unit 1, and the slave unit 4 is managed by the master unit 2. Therefore, the data signal is not unilaterally transmitted to the master units 1 and 2, and the master units 1 and 2 are not interrupted by the interruption for receiving the data signal.

"Operation of Embodiment" FIGS. 6 to 9 show the microcomputers 1b to 6b.
4 is a flowchart showing a processing procedure of transmission / reception of a data signal executed in the computer. As the procedure of asynchronous transmission, as shown in FIG. 6, first, in step 601, the collision flag and the ACK flag are reset (the functions of these flags will be described later), and then the data line 10
It is determined whether or not is unused (step 602). This determination is made by detecting whether or not the signal level of the data line 10 is at H level for a time corresponding to 1.5 bits. Then, when the determination result is affirmative (Yes), the process proceeds to the next step 603, and when the determination result is negative (NO), the same determination is performed and waits until the data line 10 is unused.

Next, in step 603, it is judged whether or not the collision flag is set, and if it is set, the routine proceeds to step 606 after the timer time TINT _{3 of} step 605 has passed, and if it is not set, step 6
Step 606 after the timer time TINT _{4 of} 04 has elapsed
Move to. In this case, the initial determination in step 603 is (NO) because the collision flag is reset in step 601. Further, the timer time TINT ₄ is set longer than the timer time TINT ₃ (the reason will be described later).

Then, in step 606, it is determined again whether or not the data line is unused. If this determination is (NO), the process returns to step 602, and if it is (YES), the process proceeds to step 607. In step 607, it is judged whether or not the data to be transmitted is D ₁ , and if it is D ₁ , step 60
It transmits a start signal STR1 moves to 8, and sends a start signal STR2 Turning to D ₁ unless step 609 (see FIG. 4). Next, in step 610, one bit of data is transmitted, and in step 611, the transmitted data is checked to determine whether a collision has occurred on the data line. This determination operation detects a match / mismatch between the data on the data line 10 and the transmitted data, and when the mismatch is detected, it is determined that a collision has occurred. It is as follows. That is, as described above, the data line 10 is configured such that the low level side has priority. Therefore, if the level of the data line 10 is low when the high level signal (bit) is transmitted, another This is the case when the unit is sending out a low level signal and there is a data collision.

For example, as shown in FIG.
When but a has transmitted in competition, leading up to the time t _0, although the transmission signal and the data lines on the data of each unit is the same, at time t _0, the unit 1 in a low-level signal Is prioritized and the level of the data line 10 becomes low. Therefore, in the sending unit 2, the mismatch of the sending data is detected, and the data collision is detected here.

If a collision is determined in step 611, step 6
Set the collision flag at 12, then step 602
Then, the process waits until the data line 10 becomes empty.
That is, when a collision is detected, the transmission is stopped and the operation of waiting for the empty data line is performed. When the data line 10 is detected to be empty in the standby state, steps 603, 605 and then steps 606, 607, 60 are performed.
At 7,608, the data D _{1 is} retransmitted. In this case, the time from passing the step 605 to detecting the availability of the timer to sending the data is the timer time TINT _3, which is shorter than the timer time TINT ₄ before the collision detection. This is because the data transmission after the collision detection is the re-transmission of the data that has been once stopped (retransmission from the data D ₁ ).
This is because the data is transmitted at a slightly faster timing.

On the other hand, when no collision is detected, the determination in step 611 is (NO), and thus the process is step 613.
Moved to and the data sent is the data end (see Fig. 4)
Is determined, and if it is not the data end, the process returns to step 610 and the data transmission for each bit is continued. When the data end is detected in step 613, the process proceeds to step 614, and it is determined whether all the data to be transmitted have been transmitted, that is, whether the transmission has been completed. If this determination is (NO), step 60
After returning to 7, data transmission of data D ₂ , data D _3, ... Is performed. If it is determined to be (YES) in step 614, it is determined in step 615 whether or not the ACK flag is set. If it is (YES), the operation is terminated and the process returns to the predetermined main routine, and (NO If so, the process proceeds to step 616 to determine whether or not there is an ACK signal (acknowledge signal). In this case, since the ACK flag is reset in the initial reset in step 601, the first determination in step 615 is (NO), and the process proceeds to step 616. Also,
The ACK signal determined in step 616 is a signal that is output when the destination unit correctly receives the transmission data. When this ACK signal is output, the determination in step 616 is (YES). , And ends the series of transmission processes and returns to the main routine.

On the other hand, if the destination unit cannot correctly receive the transmission data and does not output the ACK signal, the determination in step 616 becomes (NO) and step 617.
Then, after setting the ACK flag here, the process proceeds to step 607 to restart the retransmission from the data D ₁ .
When this re-transmission is completed, the process proceeds to step 615 through the determination of step 614. After the retransmission, the ACK flag is set, so the determination in step 615 is (Y
ES), whereby the transmission process is ended without waiting for the determination of the presence or absence of the ACK signal (step 616), and the process returns to the main routine. That is, the re-transmission is done only once and then leaves the data lines empty for other units. Further, the function of the ACK flag is a function for ending the retransmission only once, as can be easily understood from the above description.

The above is the operation of the asynchronous transmission in this embodiment.

Next, the operation of the unit on the receiving side when there is the above asynchronous transmission will be described with reference to FIG.

As a procedure of asynchronous reception, as shown in FIG. 7, first, it is determined whether or not a start signal is received (step 7).
01). This determination is made by detecting whether or not the signal level H of the data line 10 continues for a time corresponding to 1.5 bits or more. The determination result of step 701 is negative (N
In the case of O), this subroutine is immediately ended and the process returns to the main routine.

When the determination result of step 701 is affirmative (Yes), it is determined in the next step 702 whether a start bit is detected. When this determination is negative (NO), the same determination is performed, and the process waits until the start bit is detected. In this way, reading of data is started after receiving the start signal and detecting the start bit.

Next, when the start bit is detected and the determination result of step 702 is affirmative (Yes), the timer for start / stop synchronization is set to read the data (step 7
03, step 704), reading is performed at fixed time intervals by start-stop synchronization.

In the next step 705, data (16.5bit or 12b)
It)), that is, whether or not an end signal has been received. If the answer is negative (NO), the processing from step 703 is repeated. In this way, before the determination result of step 705 becomes affirmative (Yes), ST
Data of 16.5 bits or 12 bits from R to END is received. If the determination result of step 705 is affirmative (Yes), a parity check is performed to determine whether the data read in step 706 is correct. When the result of this determination is negative (NO), this subroutine is immediately terminated and the process returns to the main routine.

On the other hand, when the determination result of step 706 is affirmative (Yes), it is determined whether the received signal is data or address (step 707).

In this case, if the received data is the data D ₁ , the read data is the receiving unit address D.sub.D as shown in FIG. ADR and sender unit address S.D. AD
Since the R, determination is "ADRS" next step 707 also, if the received data is data D _2, D ₃ ......, read data from the DATA As shown, in step 707 The judgment is “DATA”.
Further, whether the received data is D ₁ or D ₂ , D ₃ , D ₄ ... Is determined by the difference in length of the start signals STR1 and STR2. Step 707 to Step 708
If the address data D. It is determined whether the ADR matches the address of its own station, and if it does not match, the reception process is immediately stopped and the process returns to the main routine. On the other hand, if it matches the address data of your own station,
In step 709, it is determined whether the reception is completed. If not completed, the above reception operation is repeated until all the data returned to step 702 is received. If it is determined to be “DATA” in step 707, the determination in step 708 is not necessary, so the process immediately proceeds to step 709.

When it is determined to be (YES) in step 709,
In step 710, an ACK signal is output as a response signal indicating that all data to be received has been completely received. As a result, the series of receiving operations is completed and the process returns to the main routine.

The above is the operation of transmission and reception in the asynchronous mode.

Next, transmission and reception operations in the synchronous mode will be described.

As a data request procedure in the synchronous transmission, as shown in FIG. 8, first, the collision flag and the ACK flag are reset (step 801) and it is determined whether or not the data line 10 is unused (step 802). Then, when the determination result is affirmative (Yes), the process proceeds to the next step 803, and when the determination is negative (NO), the same determination is performed, and the process waits until the data line 10 is unused. In step 803, it is determined whether or not the collision flag set in step 810 described later is set. When the result of this determination is negative (NO), after the elapse of the timer time TINT ₄ (step 804), the routine proceeds to the next step 806. When the determination result of step 803 is affirmative (Yes), after the elapse of the timer time TINT ₃ smaller than the timer time TINT ₄ (step 805), the process proceeds to the next step 806. In step 806, it is determined whether or not the data line 10 is unused as in step 802. If the determination result is affirmative (Yes), the process proceeds to the next step 807. The steps 801 to 806 are the same as the steps 601 to 606 of the asynchronous transmission subroutine of FIG.

Next, in step 807, STR1 is used as a start signal.
(5.5bit) is transmitted. In the next step 808, 1 bit of the data request signal of FIG. 4B is transmitted. Immediately after that, the transmission data collision is checked (step 809), and when the answer is affirmative (Yes), the collision flag is set (step 810) and step 802.
Then, the above process is re-executed. When the determination result of step 809 is negative (NO), it is determined in the next step 811 whether or not the signal (16.5 bit) is over, and when the answer is negative (NO), the processes of step 808 and subsequent steps are repeated. . The above steps 809 to 811 are executed in the same manner as steps 611 to 613 of the asynchronous transmission subroutine of FIG.

When the determination result of step 811 is affirmative (Yes), the start signal is verified, and it is checked whether the unit is in the reception mode and data is returned (step 812). If the determination result is negative (NO), it is determined whether or not the ACK flag is set (step 813). If the answer is negative (NO), the ACK flag is set (step 814) and step 807. The subsequent processing is re-executed, and the data request signal is transmitted only once again. When the determination result of step 813 is affirmative (Yes), this program is immediately terminated.

On the other hand, if the determination result of step 812 is affirmative (Yes), it is determined in the next step 815 whether or not a start bit is detected. When this answer is negative (NO), the same determination is made, and the process waits until the start bit is detected.

When the determination result of step 815 is affirmative (Yes), the timer for start / stop synchronization is set (step 816) and data is read (step 817).
Reading is performed at fixed time intervals by start-stop synchronization.

In the next step 818, it is determined whether or not the data (for 12 bits) has ended, and when the answer is negative (NO), the processing from step 816 onward is repeated. And step 8
When the determination result of 18 is affirmative (Yes), parity check is performed in the next step 819, and when this result is negative (NO), this program is immediately terminated.
When the determination result of step 819 is affirmative (Yes), the next step 820 is D ₁ , D ₂ , D of FIG. 4 (c).
₃ ... It is determined whether or not the reception of the data has been completed, and when the answer is negative (NO), the processing from step 815 onward is repeated. The determination result of step 820 is affirmative (Yes
In the case of s), an acknowledge signal (ACK) is transmitted (step 821) and this program ends. Steps 815 to 821 are steps 702 to 706 and steps 709 and 71 of the asynchronous reception subroutine of FIG.
It is executed in the same manner as 0.

As shown in FIG. 9, the procedure for data return in synchronous transmission is to first determine whether or not a start signal has been received (step 901), and if the answer is negative (NO), end this program immediately. To do.

When the determination result of step 901 is affirmative (Yes), it is determined in the next step 902 whether a start bit is detected. When this answer is negative (NO), the same determination is made, and the process waits until the start bit is detected.

When the determination result of step 902 is affirmative (Yes), a timer for start-stop synchronization is set and data is read (steps 903 and 904), and a fixed time interval is read by start-stop synchronization. Next step 90
In 5, it is determined whether or not the end of the data (16.5 bits) is reached, and if the answer is negative (NO), step 903.
The subsequent processing is repeated. If the determination result in step 905 is affirmative (Yes), parity check is performed in step 906, and if the result is negative (NO), this program is immediately terminated. When the determination result of step 906 is affirmative (Yes), the process proceeds to the next step 907. Steps 901 to 906 are the seventh
Steps 701 to 706 of the asynchronous reception subroutine in the figure
It is executed in the same manner as.

In step 907, the address of the data request signal is verified to determine whether the data request signal is the data request signal for the unit. If the result of this determination is negative (NO), this program ends immediately. When the result of this determination is affirmative (Yes), the ACK flag is reset (step 908), and the routine proceeds to the next step 909.

Next, the unit enters the transmission mode, first transmits STR2 as a start signal (step 909), and transmits 1 bit of data. Then, in step 911, it is determined whether or not the data (for 12 bits) has ended, and when the answer is negative (NO), the processing of step 910 and thereafter is repeated. Thus, the determination result of step 911 is affirmative (Y
12-bit data from STR to END is transmitted until it becomes es).

If the determination result in step 911 is affirmative (Yes), in the next step 912, D ₁ , D ₂ , and D in FIG.
₃ , it is determined whether or not the transmission (reply) of the data is completed, and when the answer is negative (NO), step 909.
The subsequent processing is repeated. Thus, by the time the determination result of step 912 becomes affirmative (Yes), D ₁ , D ₂ , D ₃ ,
Send the data of ...

When the determination result of step 912 is affirmative (Yes), ACK set by step 915 described later.
It is determined whether or not the flag is set (step 913). When the result of this determination is negative (NO), it is determined in step 914 whether or not there was an ACK (acknowledge signal). This acknowledge signal is transmitted by the data requesting unit when the data requesting unit correctly receives the return data.

When the determination result of step 914 is negative (NO), the ACK flag is set in the next step 915, and the processes of step 909 and the subsequent steps are reexecuted. In addition, step 91
When the determination result of 4 is affirmative (Yes), this program ends. The steps 911 to 915 are executed in the same manner as the steps 613 to 617 of the asynchronous transmission subroutine of FIG.

In addition, this embodiment has the following effects.

If the ACK signal is not sent from the receiving unit after the end of transmission, the same data is sent once again, so the same data is sent immediately even if there is a data transfer error. Therefore, the receiving unit can obtain correct data. Further, since the retransmission is performed only once, the same unit does not continue to use the data line 10 for the retransmission, and the data line 10 can be used efficiently.

Since the data line 10 is prioritized on the low level side, when there is a conflict in the transmission, the transmission is stopped when the higher level bit appears first, and the top portion of the data is the fourth portion.
Since it is the receiving unit address as shown in the figure, the receiving unit address can be used for prioritizing.

If the receiving unit has received data normally,
Since the ACK signal is output as the response signal, the transmitting unit can know whether the data transfer is possible or not.

[Advantages of the Invention] As described above, according to the present invention, the input / output terminals of a plurality of nodes each having a transmission / reception function for digital signals are connected by one communication line, and each node is unique. In the case where the node having the node address transmits the node address of itself and the node address of the partner as node data, and the node receiving the data includes the node address of itself on the communication line. In a transmission / reception system configured to read this data only in the first half, the communication line is configured so that one of the high and low levels has priority, and one bit of the data in the first half
Dividing into the second half period, the signal level in the first half period indicates the bit, while the signal level in the second half period is set to be the inverted signal level in the first half period, Is transmitted to the communication line or is received from the communication line, and the node transmitting the signal sequentially monitors the signal level on the communication line bit by bit and compares it with the transmitted data. Despite being the priority level, when the signal level on the communication line is the priority level, it is determined that there is data collision, the node that has determined the data collision, while stopping the transmission operation, When the signal level on the communication line becomes the non-priority level for a period corresponding to 1.5 bits of the data or more, the transmission operation is performed again. It can be achieved.

Since data can be transmitted and received between a plurality of nodes without interference by only one communication line, the system configuration can be greatly simplified.

Even if data collides on the communication line, the data sent from the node that does not stop the transmission operation is not lost, so that the reliability of communication can be secured.

To detect the empty state of the communication line, it is sufficient to detect the case where the signal level of the communication line becomes the non-priority level for a period corresponding to 1.5 bits or more. When the node that stopped the transmission operation detects this, the node repeats the transmission operation, so that the communication line can be operated with high efficiency, and the control between the nodes can be performed at high speed.

[Brief description of drawings]

FIG. 1 is a block diagram of a transmission / reception system for a vehicle to which the present invention is applied, FIG. 2 is an electric circuit diagram of the system of FIG. 1, FIG. 3 is a block diagram of a data signal, and FIG. 4 is a signal of FIG. Data format, FIG. 5 is an explanatory view showing the process of avoiding collision of two data signals, FIG. 6 is a flow chart showing the procedure of asynchronous transmission, FIG. 7 is a flow chart showing the procedure of asynchronous reception, and FIG. FIG. 9 is a flowchart showing a data request procedure, and FIG. 9 is a flowchart showing a data reply procedure. 1 to 6 ... Unit (node), 1a to 6a ... Input / output end, 1b to 6b ... Microcomputer, 10 ... Data line.

Claims (3)

[Claims] 1. The input / output terminals of a plurality of nodes having a transmission / reception function for digital signals are each connected by a single communication line, each node has a unique node address that does not overlap, and the node that transmits is its own node. A sending / receiving system configured to send out the node address of the node and the node address of the other party as node data and to read the data only when the node on the communication line includes the node address of itself. In the above, the communication line is configured so that one of the high and low levels has priority, one bit of data is divided into the first half and the second half period, and the signal level in the first half period indicates the bit, while the second half period Is set to be the signal level in the first half period inverted, and the plurality of nodes transmit the data to the communication line. Alternatively, the node receiving and transmitting from the communication line sequentially monitors the signal level on the communication line bit by bit and compares it with the transmitted data, and the signal level corresponding to the transmitted data is the non-priority level. Nevertheless, when the signal level on the communication line is the priority level, it is determined that there is data collision, and the node that has determined the data collision stops the transmission operation and the signal on the communication line is A multiplex communication system of a single communication line, wherein the transmission operation is performed again when the level becomes a non-priority level for a period corresponding to 1.5 bits of the data or more. 2. The multiple communication system for a single communication line according to claim 1, wherein the communication line is a single wire harness for a vehicle. 3. A single communication line multiplex communication system according to claim 1, wherein the nodes which are judged to have data collision transmit a non-priority level signal.