JPH05235957A - Multiplex bus access method - Google Patents

Abstract

PURPOSE:To shorten a data transmission delay time by allowing data sent at first after data revision to acquire a token by taking preceding over re- transmission data when data are sent periodically or sent for plural number of times only at data revision. CONSTITUTION:A detected value of an idle time detection circuit 15 is set by a transmission control section 12 depending on the transmission state such as 1st transmission after data revision or re-transmission in the carrier sense multiplex access system with a collision detection function. When the transmission data are periodically sent or the transmission data are sent for plural number of times at the revision of the transmission data, a bus idle time is detected longer at the 1st data transmission data after the revision in the case of re-transmission of the transmission data and a token is provided to the transmission data sent at first after the revision with priority over the data to be sent again. Thus, the transmission delay time of 1st time data transmission after data revision is reduced when the bus is frequently in use.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a CSMA / CD system (carrier sense multiple access system with collision detection function).
The present invention relates to a multiple bus access method for transmitting a message in a multiplex transmission system using the.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a device arrangement in which a conventional multiple bus access method of this type is used, and FIG. 8 is a flowchart showing its operation. In FIG. 7, 1
5 to 5 are data transmitting / receiving devices (hereinafter referred to as devices), and 6 is a bus line for connecting these devices 1 to 5. Device 1
5 has the same configuration, and the specific configuration of each one 1 will be described.

In the apparatus 1, 11 is a driver section for transmitting transmission data to the bus line 6, 12 is a transmission control section which is connected to the driver section 11 and outputs the transmission data, 13 is itself and other apparatuses 2 to 2. The receiver unit 14 for receiving the data transmitted from the bus line 6 to the bus line 6 compares the received data from the receiver unit 13 with the transmission data from the transmission control unit 12, and the device 1 on the bus line 6 From the receiver unit 13 for detecting whether or not the data from the other device and the data from the other device collide with each other, and giving a collision detection signal to the transmission control unit 12 when the data collides. Is a vacant time (fixed) detection circuit for detecting a bus vacancy and giving the information to the transmission control unit 12, and 16 is a reception control unit.

The operation of this conventional example is as follows. Figure 8
In step S1, the idle time (fixed) detection circuit 15 of the device 1 determines that the bus line 6 is not set based on the reception data received by the receiver unit 13 via the bus line 6 from any of the other devices 2 to 5. It is determined whether or not it is empty. If the determination is NO, this operation is repeated, and if YES, the process proceeds to step S2, where the bus line 6 after the end code as shown in FIG. It is determined whether or not, and if the determination in step S2 is NO, step S
Return to 1.

When the determination in step S2 is YES, in steps S3 and S4 the transmission controller 12 transmits the start code and data as transmission data to the bus line 6 via the driver 11 as shown in FIG. The transmission data in this case is transmitted in the order of, for example, a start code (fixed), priority data (variable between high, medium, and low), data (variable), and end code (fixed).

Here, for example, as shown in FIG. 10 as an example at the time of data collision, when the transmission data are simultaneously transmitted from the other devices 2 to 5 onto the bus line 6, the priority data having the highest priority is given. Those who have will get the transmission right. For example, as shown in FIG. 11, when “1” is transmitted from the device 1 and “0” is transmitted from the device 2 as the priority data (arrow A in the figure), “0” is “1” in the circuit configuration. "
Therefore, the transmission data “0” exists on the bus line 6.

Therefore, in step S5, the comparison unit 1 of the device 1
4 receives the above data via the receiver unit 13, compares the transmission data of the device 1 and the reception data from the bus line 6 to determine whether or not the data collide, and when the two data are different from each other. Indicates that there is a collision, the determination in step S5 is YES, and in the next step S6, the transmission controller 12
Then, a collision detection signal is sent to interrupt the transmission of the transmission data, and then the process returns to step S1 to repeat the above operation.
On the other hand, when both data are the same, there is no collision and the determination in step S5 is NO, the data is transmitted in the next step S7, the message end code is transmitted in step S8, and the data transmission is completed in step S1. Return to.

In the example shown in the figure, "0" has priority over "1". Therefore, if the priority data is 8 bits, "0"
"0000000" has the highest priority, and "111111"
11 ”is the lowest.

As described above, the conventional CSMA / C
In the multiple bus access method using the D method, the devices (nodes) 1 to 5 that want to transmit after detecting a certain bus idle time (T shown in FIGS. 9 and 10) all at once send a message start code and priority. The data, data, and message end code are sequentially transmitted in this order as shown in FIG. When a plurality of devices (nodes) simultaneously send out messages, the data transmitted from the device itself and the data from other devices on the bus line 6 are compared in the priority data area to perform arbitration processing, When the transmission data from the device and the data on the bus line 6 are different, the transmission is interrupted, the constant bus idle time (T) is detected, and then the bus line 6 is accessed again. The device having the priority data is configured to acquire the transmission right.

[0010]

A method of improving transmission reliability by using a method of transmitting data periodically or a method of transmitting a plurality of times only at the time of updating in the above-mentioned conventional multiple bus access method is further known. There is. However, in this method, when the priority data in the message is fixed, the state in which the retransmission data acquires the transmission right prior to the data transmitted for the first time when updating occurs, and the data transmission delay time deteriorates. There is a point.

In order to solve this, there is known a method of changing the priority data in the message according to the data transmission state (for example, the first transmission data after updating has a high priority and a retransmission data priority is low). However, this method has a problem that the processing becomes complicated and the scale of the hardware increases because the determination in the data transmission state is required in addition to the priority controlled by the data content originally.

Therefore, in view of the above-mentioned conventional problems, the present invention adopts a method of transmitting data periodically or a plurality of times only when updating data, in which case the data transmitted for the first time after updating is It is an object of the present invention to provide a multiple bus access method that is configured to acquire a transmission right prior to data to be retransmitted and to reduce a data transmission delay time.

[0013]

In order to achieve the above object, the multiple bus access method according to the present invention is a CSM.
In the A / CD-based multiplex transmission system, when the transmission data is transmitted periodically or when the transmission data is transmitted multiple times only when the transmission data is updated, the bus idle time is set as the initial data after the data update when the data is retransmitted. It is characterized in that it is detected longer than at the time of transmission, and the transmission right is given to the transmission data transmitted for the first time after the update by giving priority to the data to be retransmitted.

[0014]

With the above configuration, the bus vacancy detection time is changed according to the number of times data is retransmitted and the vacancy time is detected for a long time, so that data is updated in a state where the bus is frequently used due to data retransmission from each device. It is possible to reduce the transmission delay time of subsequent initial data transmission and preferentially transmit a message with a small number of retransmissions.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a multiplex transmission system using a CSMA / CD system (carrier sense multiple access system with a collision detection function) for implementing a multiple bus access method according to the present invention, and its basic configuration is completely the same as that of the conventional example of FIG. The same, 1 to 5 are data transmission / reception devices (hereinafter referred to as devices),
Reference numeral 6 is a bus line connecting the above devices 1 to 5. In each device, 11 is a driver unit, 12 is a transmission control unit,
Reference numeral 13 is a receiver section, 14 is a comparison section, 15 is a free time (variable) detection circuit, and 16 is a reception control section.

FIG. 2 is a block diagram showing an example of application of a multiplex transmission system for carrying out the method of the present invention to a vehicle. In the figure, 21 to 30 are left front data transmission / reception device, right front data transmission / reception device, and meter, respectively. A data transceiver, instrument panel data transceiver, left front door data transceiver, left rear door data transceiver, right front door data transceiver, right rear door data transceiver, left tail data transceiver, right tail data transceiver.

Further, FIG. 3 is a flow chart showing the operation of this embodiment, FIG. 4 is a timing diagram for updating the transmission data of this embodiment, FIG. 5 is a timing diagram for retransmitting the transmission data of this embodiment, and FIG. FIG. 6 is a timing chart of a specific example of this embodiment.

Next, the operation will be described. In FIG. 3, the idle time (variable) detection circuit 15 of the device 1 shown in FIG. 1 in step S11 converts the received data received by the receiver unit 13 via the bus line 6 from any of the other devices 2-5. Based on this, it is determined whether or not the bus line 6 is vacant. If the determination is NO, this operation is repeated. If the determination is YES, then in step S12 the transmission of the device is the first transmission after the transmission data update. Determine whether or not. Otherwise, if the determination is NO, the process proceeds to step S13, and if the determination is YES, the process proceeds to step S14.

In the present invention, the idle time of the bus (variable)
The detection value of the detection circuit 15 is set by the transmission control unit 12 according to the transmission state such as the first transmission or the re-transmission after the data update, and when the transmission data is re-transmitted, as shown in FIG. 4 and FIG. The detection of the bus idle time is longer than that at the time of the first data transmission, and in the case of FIG. 5, it is configured to perform nT time. That is, in step S13, the idle time (variable) detection circuit 15 of the device (1) is
However, as shown in FIG. 5, it is determined whether or not the bus is vacant for nT time based on the received data, and the determination is YES.
If so, the process proceeds to step S15 to retransmit the data, and if the determination is NO, the detection operation of this step is repeated until nT time is reached.

In step S14, the vacant time (variable) detection circuit 15 of the device 1 determines whether the bus vacancy continues for T time as shown in FIG. 4, and the determination is YES.
In this case, the process proceeds to step S15, the transmission control unit 12 is caused to transmit the start code as shown in FIG. 4, and the initial data transmission after the data update is performed. When the determination is NO, that is, when the bus has not been idle for T time, the process returns to step S11 and the above operation is repeated. In step S16, the priority data is output from the transmission controller 12 as in the conventional example shown in FIGS.

Further, in step S17, the comparison unit 14 of the apparatus
Compares the transmission data of its own device 1 with the reception data from the bus line 6 and determines whether or not the data collide. If they are different, it means that there is a collision and the determination is YES.
Then, in step S18, the transmission control unit 12 suspends the transmission and returns to step S11. On the other hand, when both data are the same, there is no collision, the determination is NO, and the process proceeds to step S19 to output the data to the transmission control unit 12. After that, the process proceeds to step S20, the message end code is output to complete the data transmission, and then the process returns to step S11.

FIG. 6 is a timing chart showing a concrete example of the above embodiment in which the transmission reliability is improved by transmitting data three times every data update. The operation of this specific embodiment is as follows.

A) As shown in a) of the figure, regarding the transmission of the initial transmission data after the end of the data update, the message is transmitted when the following conditions are satisfied. (1) When the bus idle state continues for “T” time from the detection of the end code of the previous message, or (2) Other devices until the bus idle state of “T” time is detected from the detection of the end code of the previous message ( When the sending of a message from a node) is detected.

B) As shown in b) of the figure, regarding the first transmission of the transmission data, the message is transmitted when the following conditions are satisfied. (1) When the bus idle state continues for "3T" time from the detection of the end code of the previous message, or (2) "3T" time after detecting the bus idle state of "2T" time from the detection of the end code of the previous message. When sending of a message from another device (node) is detected before the bus free state of is detected.

C) Regarding the second transmission of the transmission data as shown in c) of the figure, a message is transmitted when the following conditions are satisfied. (1) When the bus empty state continues for "5T" time from the detection of the end code of the previous message, or (2) "5T" time after detecting the bus empty state of "4T" time from the detection of the end code of the previous message. When the message transmission of another device (node) is detected until the bus idle state of is detected.

[0026]

As described above, according to the present invention, even when the data is retransmitted to improve the communication reliability and the bus is frequently accessed, the message contents (priority data, priority data, (Data), the first transmission data has priority over the re-transmission data to obtain the transmission right, thereby reducing the data transmission delay time, and giving the transmission right by giving priority to the message with a small number of retransmissions. There is an effect that a quick backup can be performed at the time of occurrence.

[Brief description of drawings]

FIG. 1 is a block diagram showing a multiplex transmission system using a CSMA / CD method for implementing a multiplex bus access method according to the present invention.

FIG. 2 is a block diagram showing an example of use of the system of FIG.

FIG. 3 is a diagram showing a flowchart for explaining the operation of the embodiment of the present invention.

FIG. 4 is a timing diagram when updating transmission data in the embodiment of FIG.

5 is a timing diagram at the time of retransmission of transmission data in the embodiment of FIG.

FIG. 6 is a timing diagram of a specific example of the embodiment of FIG.

FIG. 7 is a block diagram showing a system for implementing a conventional method.

FIG. 8 is a timing diagram showing the operation of the conventional method.

FIG. 9 is a timing chart of data transmission in the conventional example.

FIG. 10 is a timing chart at the time of data collision in the conventional example.

FIG. 11 is a specific timing chart at the time of data collision in the conventional example.

[Explanation of symbols]

 1 to 5 data transmitter / receiver (device) 6 bus line 11 driver unit 12 transmission control unit 13 receiver unit 14 comparison unit 15 idle time detection circuit

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[Procedure amendment]

[Submission date] June 11, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

C) Regarding the second transmission of the transmission data as shown in c) of the figure, a message is transmitted when the following conditions are satisfied. (1) When the bus empty state continues for "5T" time from the detection of the end code of the previous message, or (2) "5T" time after detecting the bus empty state of "4T" time from the detection of the end code of the previous message. When the sending of a message from another device (node) is detected before the bus free state of is detected.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 is a timing chart at the first transmission after updating the transmission data in the embodiment of FIG.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

FIG. 8 is a diagram showing a flowchart for explaining the operation of the conventional method.

Claims (1)

[Claims] 1. In the CSMA / CD multiplex transmission system, when the transmission data is transmitted periodically or when the transmission data is transmitted a plurality of times only when the transmission data is updated, the bus idle time is set as the data when the data is retransmitted. A multiple bus access method, characterized in that the data is detected longer than when the initial data is transmitted after the update, and the transmission right is given to the transmission data transmitted for the first time after the update by giving priority to the data to be retransmitted.