JPH0666784B2 - Priority setting method in multiplex communication - Google Patents

Description

The present invention relates to a priority setting method in multiplex communication suitable for use in, for example, a multiplex communication system 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, a multiplex communication system has been developed in which a plurality of nodes can transmit and receive by one communication line. FIG. 3 is a block diagram showing the configuration of a transmission / reception system adopting this multiplex communication system.

In the figure, 1 is an audio unit (node) mounted on a vehicle, 2 is an air suspension unit (node) for adjusting the vehicle height, and 3 and 4 are radio switch units for controlling the above-mentioned units, respectively. (node)
And air suspension switch unit (node)
Is. The radio switch unit 3 and the air suspension switch unit 4 are operated by the driver. Reference numeral 5 is a radio switch unit for a passenger to operate, and reference numeral 6 is a display unit (node) for displaying the operating states of the audio unit 1 and the air suspension unit 2.

The input / output terminals of each of the units 1 to 6 described above are connected to one data line 10, respectively.
Data is transmitted and received only through 0.
Also, as can be seen from the above description, each unit is a LAN.
(Local Area Network).

Next, 1b to 6b are communication control units for controlling the exchange of data of the units 1 to 6, respectively, and each have a built-in microcomputer. In this case, the output terminal 1c of the communication controller 1b is connected to the base of the transistor Tr via a resistor as shown in FIG. Transistor T
In r, the collector is connected to the positive power supply terminal (voltage Vcc), is connected to the data line 10 via the input / output terminal 1a, and the emitter is grounded. Also,
The input end 1d of the communication control unit 1b is directly connected to the input / output end 1a. The communication control units 2a to 6a in each of the units 2 to 6 have the same configuration as that of the communication control unit 1b described above.

The characteristics of the data line 10 will be described below.
This data line 10 is connected to the correlator of the transistors at the input / output ends of each of the units 1 to 6. Therefore, if any one of the transistors Tr is turned on, it will be forced regardless of the states of the other transistors Tr. The ground level (low level). That is, the data line 10 is configured to give priority to the low level side, and when any one of the units 1 to 6 outputs the low level signal, the other units cannot output the high level signal. It is composed.

Next, the exchange of data in each of the units 1 to 6 will be described.

The signals output from the units 1 to 6 are start-stop synchronization signals as shown in FIG.
TR (1 or 5.5 bits), high-level start bit S, data part B (8 bits), parity bit, and high-level end signal. The start bit, data bit B, and parity bit are The 0.5 bits in the first half represent the contents of that bit (see drawing S or D), and the 0.5 bits in the latter half are the gap G at the level obtained by inverting the contents of the bits. The reason why the gap G is provided in this manner is, in part, to facilitate detection of the usage state of the data line 10. That is, according to the above-mentioned signal form, as shown in FIG. 5, when the signal is being output, it is always at a low level for a period exceeding at least 0.5 bit. Therefore, 0.5
By detecting whether or not the state of the line is at the low level for a period exceeding one bit (for example, one bit), it is possible to know whether or not the data line 10 is in use.

Data transfer between the audio unit 1, the air suspension unit 2 and the display unit 6 is unidirectional data transfer as shown in FIG. 3, and asynchronous transmission is performed. The form of transmission data in this asynchronous transmission is as shown in FIG. 6 (a). The data D ₁ shown in this figure is address data composed of a receiving unit address (that is, the address of the display unit address 6) and a transmitting unit address,
Further, the data D _{2 and} thereafter are various data used for display. In this case, the start signal STR of the data D ₁
Is set to 5.5 bit (hereinafter referred to as STR 1), the start signal STR of the data _D 2, _{D 3} ...... is set to 1 bit (hereinafter referred to as STR 2). Therefore, the display unit 6 determines whether the start signal is STR1 or STR.
By determining whether it is 2, it is possible to know whether the received data is address data or display data.

Next, the audio unit 1 and the radio switch units 3 and 5 are in a slave relationship with the master,
Similarly, the relationship between the air suspension unit 2 and the air suspension switch unit 4 is also a slave relationship with the master. Then, for the data exchange between the master and the slave, first, the master side outputs the data request signal shown in FIG. 6 (b), and then the slave side is shown in the same figure (c) under the control of the master side. It is designed to output a data reply signal. The bidirectional arrow shown in FIG.
The direction of data transfer is shown. The data request signal in this case is a signal of only the data D _{1 as} shown in FIG. 6 (b), and this data D ₁ is the same signal as the data D ₁ shown in FIG. 6 (a). Further, the data reply signal is composed of data of only data components as shown in FIG. 7C, and the data D ₁ , D ₂ ... Shown in this drawing are shown in FIG.
The data is the same as the data D ₂ , D ₃ ...

Next, in the above system, an operation of avoiding data collision when two or more units compete with each other to start transmission will be described.

Now, as shown in FIG. 7, it is assumed that the audio unit 1 and the air suspension unit 2 on the master side simultaneously start transmission. The transmission signal in this case is shown in FIG.
Since it is one of the signals shown in (a) and (b), the address data of the receiving unit is sent out after the start signal and the start bit. And until time t ₀ ,
Audio unit 1 and air suspension unit 2
And the same data, and these data are different after time t ₀ .

In this case, before time t ₀ , the level of the data line 10 is equal to the level of the output signals of the units 1 and 2, but at time t ₀ , the level of the output signal of the air suspension unit 2 is the same. It will be different from the level. This is data line 1 as described above.
This is because 0 is configured with priority on the low level side,
This is because the low level signal of the audio unit 1 at t ₀ has priority. In the air suspension unit 2, the level of the output signal and the data line 10
When a difference in level is detected, it is determined that a data collision has occurred. As a result, a collision is detected at time t ₀ , and the air suspension unit 2 thereafter suspends transmission. Then, only the audio unit 1 continues the transmission, and the collision is avoided. The collision detection of the audio unit 1 is performed in the same manner as above. In the conventional system, the data collision is avoided as described above, and as a result, the data can be exchanged between a plurality of units by one communication line.

Further, in the conventional system, as can be seen from FIG. 7, the priority is set by the address of the receiving unit, and the smaller address has the higher priority. That is, as long as the low level signal is continuously transmitted, the transmission is not stopped due to the collision of the transmission data.

The above is disclosed in the applicant's prior application (Japanese Patent Application No. 60-157807).

"Problems to be Solved by the Invention" However, the above-described conventional system has the following drawbacks.

Even if a collision actually occurs, in order to detect a data inconsistency, it is not possible to determine a collision without waiting for the data portion following the start bit, so a collision was detected and transmission was stopped. In that case, it is a dead time in the calculation processing time of the transmitter. For example, in the case shown in FIG. 7, there is a dead time from the start of transmission of the air suspension unit 2 to time t ₀ .

Since the priority is decided by the address of the node,
It is difficult to change the priority order, and it is impossible to arbitrarily change the priority order regardless of the address.

When the clock accuracy of the output signal is different for each node, the sampling frequency of the read data in the receiver becomes higher than the frequency of the data, and it has been difficult to send a large amount of data in a short time. This point will be described below.

Now, assuming that FIG. 8 (a) is an output signal waveform with a high precision clock and FIG. 8 (b) is an output signal waveform with a low precision clock, and the start signal is a signal deviated by Δd, the data line The change in level at 10 is as shown in FIG. 7C because the low level side is prioritized. In this case, although the error Δd is enlarged in the figure for explanation,
Actually, it is a slight error. Since the data mismatch detection for determining the collision is generally set to be insensitive to the deviation degree due to the error of the clock accuracy, in the case shown in FIG. Not done. Therefore, in the state shown in FIG. 8, both signals continue to be output with a phase difference of Δd.

On the other hand, since the node receiving the above signal receives the waveform shown in FIG. 8 (c), it receives a signal whose rising timing is later than normal and the period of high level is shorter than normal. Then, since the read timing of the received signal is performed at every predetermined interval from the rising edge of the start signal, if the high level state changes as described above, for example, a read error occurs at time t ₂ shown in FIG. (The reading timing is originally time t ₁ ). To avoid such read errors,
The read sampling frequency of the received signal needs to be higher than that of the input signal, and a large amount of data cannot be sent fast.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a priority order setting method in multiplex communication capable of eliminating all the above-mentioned drawbacks.

[Means for Solving Problems] In order to solve the above problems, the present invention has a plurality of nodes having a transmitting / receiving function, and each of the input / output terminals of each node has one communication line. In addition, the communication line is configured such that either the high level or the low level is prioritized, and one bit of data is divided into the first half / second half period, and the signal level in the first half period indicates the bit. ,
The node that sets the signal level in the second half period to be the signal level in the first half period inverted, and the plurality of nodes transmits or receives the data to or from the communication line, The signal level on the communication line is sequentially monitored bit by bit and compared with the output data, and the signal level on the communication line is the priority level even though the signal level corresponding to the output data is the non-priority level. In this case, in the multiplex communication system configured to stop the transmission operation, the node that determines that the data has collided and that has collided the data is provided with a start signal at the beginning of the transmission signal, and The signal level is set to the priority level of the communication line, and the length of the start signal is set to 1.5 bits or more in order of increasing priority. It is characterized in.

"Operation" When multiple nodes start transmission at the same time, the start signal has a length, so the data does not match when the start signal ends, except for the node that has issued the longest start signal among the competing nodes. Is detected and transmission is stopped, so that only the node issuing the longest start signal at that time continues transmission.

When the interrupting node outputs a start signal, the node that is transmitting detects a mismatch with the transmitted data and stops the transmission operation, while the node that is interrupting starts transmitting.

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

FIG. 1 is a waveform diagram showing a waveform of a transmission signal in one embodiment of the present invention. It should be noted that this embodiment is an embodiment in which the method according to the present invention is applied to the multiplex communication system shown in FIG.

In this embodiment, as shown in FIGS. 1 (a), 1 (b) and 1 (c), the length of the start signal STR1 is different. The length of the start signal STR1 in this case is set to a predetermined length for each receiving unit, each transmitting unit, or each type of data to be transmitted. However, the start signal STR1 is the start signal ST
It is set longer than R2 so that they are not confused.

As described above, if the lengths of the start signals STR1 are made different, if the transmissions compete, the longer start signal will preferentially acquire the reception right. For example, Figure 1 (a), (b)
If the signals shown in FIG. 2 compete with each other, the shorter one of the start signals STR1 as shown in FIGS. 2 (a) and 2 (b) first detects a data mismatch and stops transmission. That is, the figure (b)
Immediately after the start signal STR1 shown in FIG. 3 is finished, the start signal STR1 shown in FIG. 6 (a) is still continuing, so the level of the data line 10 is at a low level, and as a result, FIG. That is, the transmission signals shown in the table have data mismatches at the monitor point P ₁ .

Comparing FIG. 2 with FIG. 7 described above, it can be seen that the dead time until the non-priority side stops transmission is significantly reduced in this embodiment.

Further, as shown in FIG. 8, even when the clock accuracy is different between the units, the difference in length of the start signal STR1 is usually sufficiently larger than the clock error, so that the start signal STR1 is the longest signal. except,
Be sure to stop the transmission so that no two or more units continue to transmit in parallel. Therefore, FIG.
A signal having a timing shift as shown in (c) is not output to the data line 10, and there is no concern that the receiving unit may cause a reading error.

If one node continues the transmission operation and another node outputs a start signal to perform the interrupt transmission, the level of the communication line is irrelevant to the transmission data which has continued the transmission operation. It becomes the priority level for 1.5 bits or more. Therefore, the node that has continued the transmission operation detects the mismatch with the transmission data and stops the transmission operation, and instead, the transmission operation of the node that performs the interrupt is started.

Therefore, when there is a transmission request, it is preferable for the data communication system that it is preferable to interrupt the transmission and perform the transmission even if another node is transmitting.

[Advantages of the Invention] As described above, according to the present invention, a plurality of nodes having a transmission / reception function are provided, and the input / output terminals of each of the nodes are connected by one communication line. Configure the communication line so that either level has priority,
One bit of data is divided into the first half / second half period, and the signal level in the first half period indicates that bit, while the signal level in the second half period is set to be the inverted signal level in the first half period, The plurality of nodes transmit the data to the communication line or receive the data from the communication line, and the node transmitting the data sequentially monitors the signal level on the communication line bit by bit and compares it with the transmission data. Although the signal level corresponding to is a non-priority level, when the signal level on the communication line is a priority level, it is determined that there is data collision, the node that has determined the data collision, In a multiplex communication system configured to stop the transmission operation, a start signal is provided at the beginning of the transmission signal, and the level of the start signal is set to the priority level of the communication line. As well as, the length of the start signal, a 1.5 or more bits, since the longer the order of priority, it is possible to achieve the following effects.

When a plurality of nodes start transmission at the same time, the node with lower priority stops transmission earlier in the period of the start signal, so that the dead time until the transmission is stopped can be significantly shortened.

In this case, the priority order can be set individually and independently regardless of the node address or the like. Moreover, since the change can be easily and quickly made, the priority order can be changed according to the change of the data processing situation.

A large amount of data can be sent in a short time without having to increase the data frequency so much with respect to the data reading sample frequency.

Even if another node is transmitting, it can be interrupted and interrupted for preferential transmission, so if it is preferable to incorporate interrupt communication processing as a system operating state, it is extremely useful. It is suitable.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a transmission signal in one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the transmission stop processing after collision detection in the embodiment, and FIG. 3 is mounted on a vehicle. FIG. 4 is a block diagram showing the configuration of the multiplex communication system, FIG. 4 is a circuit diagram showing the configuration of the data line 10 of the system shown in FIG. 1, FIG. 5 is a waveform diagram showing an output signal in the system, and FIG. FIG. 7 is a conceptual diagram showing an aspect of transmission data in the system, FIG. 7 is a waveform diagram for explaining transmission interruption processing when the conventional priority setting method is used, and FIG. 8 is a case where clock accuracy is different for each node. It is a waveform diagram for explaining a read error that occurs. 1 to 6 ... Unit (node), 1a to 6a ... Input / output terminal, 1b to 6b ... Communication control unit, 10 ... Data line, STR1 ... Start signal.

Claims (1)

[Claims] 1. A plurality of nodes having a transmission / reception function,
In addition, the input / output terminals of each node are connected by one communication line, and the communication line is configured such that one of the high and low levels has priority, and one bit of data is divided into the first half and second half periods. , 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, and the plurality of nodes transmit the data to the communication line. The node transmitting or receiving from the communication line and transmitting the signal sequentially monitors the signal level on the communication line bit by bit and compares it with the output data, and the signal level corresponding to the output data is the non-priority level. Nevertheless, if the signal level on the communication line is the priority level, it is determined that there is data collision, and the node that determines data collision is configured to stop the transmission operation. In the multiplex communication system, the start signal is provided at the beginning of the transmission signal, the level of the start signal is set to the priority level of the communication line, and the length of the start signal is 1.5 bits or more. A method of setting priorities in multiplex communication, characterized in that the priorities are set longer in descending order of priority.