JP2001036553A - Data communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data communication system that can surely detect collision of data on a communication path without the use of an dedicated hardware. SOLUTION: A navigation device 2 adds collision detection data to a head of a frame at the transmission of a frame. Specific contents are set to the collision detection data by each device connected to a bus 5, and on the occurrence of two frames or over on the bus 5, the contents are destroyed without fail. A frame collision discrimination section 68 corresponding to a data transmission source compares added data actually sent/received on the bus 5 with additional data corresponding to its own device to detect collision of frames on the bus 5 in the case of dissidence. The frame collision discrimination section 86 corresponding to the data transmission destination compares additional data corresponding to each device connected to the bus 5 with additional data actually sent/received on the bus 5 to detect collision of frames on the bus 5 when they are dissident.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication system for asynchronously transmitting and receiving data between a plurality of devices, processors and the like.

[0002]

2. Description of the Related Art Conventionally, in asynchronous communication in which a plurality of data communication devices perform data communication using one communication medium, two data communication devices are used.
Simultaneous data transmission from one or more data communication devices may cause data destruction due to collision between transmitted data. When data is destroyed, the content of the transmitted and received data changes,
It is necessary to detect the occurrence of data collision in the transmission source device or the transmission destination device.

There are the following two typical methods for detecting destruction due to data collision. The first method is to provide a dedicated detection circuit for detecting data collision on a communication path. For example, if it is assumed that "0" is transmitted preferentially when each bit data of "0" and "1" collide on a communication path, the detection circuit provided in each transmission source device may be configured to transmit its own data. If the data "1" transmitted by the user has changed to "0" on the communication path, it is determined that the data transmitted by itself and the data transmitted by another transmission source have collided. Since a dedicated detection circuit is used, data collision can be detected in a short time, and transmission of the next data can be stopped, so that only high-priority data remains on the communication path. .

[0004] A second method is to continue transmitting data even if data collide on a communication path, and to detect data destroyed by the collision. For example, data destruction can be detected by examining the contents of the CRC code and the parity added in byte units in the data.

[0005]

However, the method of detecting a data collision using the above-described dedicated circuit requires special hardware for detecting the data collision, which leads to an increase in cost. There's a problem. In addition, when a general-purpose microcomputer for communication (hereinafter, referred to as a “microcomputer”) is used, since the above-described circuit for collision detection is often not provided, available microcontrollers are limited. The degree of freedom may be impaired.

In the method of detecting data collision by examining the contents of data using a CRC code or the like, even though the data is destroyed by collision, a correct CRC is accidentally obtained.
In some cases, a C code was obtained, and data collision could not be reliably detected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a data communication system capable of reliably detecting data collision on a communication path without using dedicated hardware. Is to provide.

[0008]

In order to solve the above-mentioned problems, in the data communication system of the present invention, when a frame is allowed to be transmitted on the condition that there is no frame transmitted on a communication path, a frame is transmitted. The additional data unique to the transmission source is added to the frame and transmitted to the communication path, and the collision of the frame on the communication path is detected based on the contents of the additional data actually transmitted to the communication path. By using additional data unique to each transmission source, when the additional data collide with each other on the communication channel, a part of the content is always destroyed, so that it is possible to reliably detect the collision between frames. it can. In addition, since it is only necessary to detect the collision of the frame, it is not necessary to use a dedicated circuit by hardware, and the cost of parts and the like can be reduced.

It is preferable that the collision detecting means provided at the transmission source of the frame detects a frame collision when additional data having a content different from that of the additional data transmitted by itself is detected. Since only the additional data transmitted by itself needs to be compared, the processing can be simplified.

The collision detecting means provided at the transmission destination of the frame includes the additional data corresponding to the frame received via the communication path in the list of additional data specific to the transmission source of the frame. It is desirable to detect frame collisions when not present. By providing the additional data of each transmission source as a list and making it a comparison target, it is possible to reliably detect a frame collision.

In the case where the transmission and reception of a frame through a communication path is performed in the form of serial data, it is desirable that a plurality of consecutive bits of the above-mentioned additional data have the same content. Even if the transmission timing of the frame transmitted on the communication path is shifted, it is possible to reliably detect the collision of the frame within a range of a plurality of consecutive bits.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A data communication system according to an embodiment of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a diagram showing the overall configuration of a data communication system according to a first embodiment. The data communication system of the present embodiment shown in FIG. 1 includes a voice recognition device 1, a navigation device 2, a CD changer 3, and an audio device 4, which are connected via a bus 5.

The voice recognition device 1 performs a voice recognition process on an operation voice generated by a user's voice, and the recognition result is transmitted by data communication via a bus 5 to another device such as the navigation device 2 or the audio device 4. Sent to the device. The navigation device 2 detects the position of the vehicle and displays a map around the position of the vehicle, searches for a route to a destination selected by the user, performs route guidance, and the like.

The CD changer 3 is loaded with a plurality of CDs, reads signals recorded on the recording surface of the CD selected by the user, and reproduces music and the like. The audio device 4 is an all-in-one type audio device included in one housing accommodated in a dashboard in a vehicle compartment, and includes, for example, an operation panel having various operation keys in addition to a radio tuner and a cassette tape deck. I have. Various operation instructions given using this operation panel are given to the CD changer 3, the voice recognition device 1, etc., in addition to those given to the radio tuner and the cassette tape deck included in the audio device 4 itself. There are also things. When an operation is performed on a device other than the audio device 4, an operation signal corresponding to the operation state is sent to the other device by data communication via the bus 5.

Next, the case where data communication is performed between the navigation device 2 and the audio device 4 will be described in detail. For example, a case where a predetermined frame is transmitted from the navigation device 2 to the audio device 4 will be described. FIG. 2 is a diagram illustrating a detailed configuration of the navigation device 2 and the audio device 4.

The navigation device 2 shown in FIG. 2 includes a navigation processing unit 20 and a data transmission unit 22. The navigation processing unit 20 performs a predetermined navigation operation such as a display process of a map image around the own vehicle position, a route search process, and a route guidance process.
For example, a frame indicating a voice interrupt request transmitted to the audio device 4 when performing voice guidance during route guidance is output to the data transmission unit 22. The data transmission unit 22 converts the data output from the navigation processing unit 20 into a communication format and transmits the data to another device. The transmission data generation unit 60, the transmission data buffer 62, It includes a data setting unit 64, a transmission processing unit 66, a frame collision determination unit 68, and a frame end determination unit 70.

The transmission data generating section 60 generates a frame by adding various data necessary for data communication to the transmission data output from the navigation processing section 20.

FIG. 3 is a diagram showing a data structure of a frame generated by the transmission data generating section 60. As shown in FIG. 3, the frames are sequentially assigned a communication type (T
YPE), destination address (DA), source address (SA), data length (LEN), transmission data (DAT)
A) and error detection data (ERR).

The communication type defines the type of communication using this frame. For example, normal one-to-one communication, broadcast communication, response, and the like are specified. In the transmission destination address, an address corresponding to a device to which the frame is transmitted is stored. The source address stores the address corresponding to the device that is the source of the frame. In the present embodiment, an address corresponding to the audio device 4 is stored in the destination address,
An address corresponding to the navigation device 2 is stored in the transmission source address.

The data length represents the data length of data to be transmitted (DATA shown in FIG. 3) in byte units. As the transmission data, data to be transmitted is stored. For example, the navigation processing unit 2
Data indicating a voice interrupt request output from 0 corresponds to this. The error detection data is added to detect an error in the content of each data from the communication type to the transmission data included in the frame. As the error detection data, for example, checksum data, a CRC code, or the like is used.

The transmission data buffer 62 temporarily stores the frame generated by the transmission data generation unit 60. The head data setting unit 64 adds 1-byte “collision detection data” having predetermined contents set for detecting a collision of a frame on the bus 5 to the frame.

FIG. 4 is a diagram for explaining a frame to which collision detection data is added. As shown in FIG.
The head data setting unit 64 adds the above-described collision detection data to the head of the frame stored in the transmission data buffer 62. As this collision detection data, a unique value is used for each device connected to the bus 5, and when a frame collision occurs on the bus 5, the collision actually transmitted to the bus 5 By examining the contents of the detection data,
A frame collision determination is performed.

Next, the contents of the collision detection data will be specifically described. FIG. 5 is a diagram illustrating an example of the collision detection data. In the present embodiment, the collision detection data is 8 bits, and only one of the 8 bits is set to "1" and the other 7 bits are set to "0". . In this case, the contents of the collision detection data include 01h and 02 as shown in FIG.
h, 04h, 08h, 10h, 20h, 40h, 80h
8 patterns are conceivable. Note that "h" added to the above-described collision detection data indicates that the data is a hexadecimal number. In the present embodiment, the above-described eight patterns of collision detection data are made to correspond to the respective devices connected to the bus 5. Specifically, for example, as shown in FIG.
1h corresponds to the voice recognition device 1, 02h corresponds to the navigation device 2, 04h corresponds to the CD changer 3, and 08h corresponds to the audio device 4, respectively.

The transmission processing unit 66 includes a transmission data buffer 6
2, the frame (the frame after the collision detection data is added) is read out byte by byte and converted into serial data, and a start bit “0” is added at the beginning.
A parity (for example, even parity) and a stop bit “1” are added to the rear part, respectively, and transmitted on the bus 5.

The frame collision judging section 68 extracts the data of the first byte of the frame transmitted / received on the bus 5 and the content of the collision detection data added to the first byte of the frame output from the transmission processing section 66. It is determined whether or not they match. If they do not match, the frame collision determination unit 68 instructs the transmission processing unit 66 to retransmit the frame.

The frame end judging section 70 judges the end of a frame transmitted and received on the bus 5 and outputs a frame signal. For example, a high-level frame signal is output after a lapse of a predetermined time since there is no more data transmitted and received on the bus 5. This frame signal is transmitted to the transmission processing unit 66
Is used as a signal for permitting the transmission operation by. That is, the transmission processing unit 66 sets the condition that the frame signal is output from the frame end determination unit 70,
That is, frame transmission is performed on the condition that there is no frame transmitted on the bus 5 at that time.

As shown in FIG. 2, the audio device 4 includes an audio processing unit 40 and a data receiving unit 42. The audio processing unit 40 realizes various functions of the audio device 4, and includes a radio tuner, a cassette tape deck, a power amplifier, and the like. The data receiving unit 42 is for receiving a frame transmitted from the navigation device 2 or another device, and includes a reception processing unit 80, a reception data buffer 82, a collision detection data table storage unit 84,
The configuration includes a frame collision determination unit 86.

When a frame is input in the form of serial data, the reception processing unit 80 detects a start bit and a stop bit and extracts data in byte units (if parity is included, the data is further extracted). After performing an error check using parity), this data is sequentially converted to parallel data to restore the frame shown in FIG. Then, after performing error detection processing using the error detection data and the like included in the frame, various data except for the transmission destination address and the error detection data and the like included in the frame are output to the reception data buffer 82. I do.

The reception data buffer 82 includes a reception processing unit 8
Various data output from 0 are temporarily stored. When this data storage operation is completed, a notification to that effect is sent from the reception data buffer 82 to the audio processing unit 40.

The collision detection data table storage unit 84
A table corresponding to the above-described collision detection data list shown in FIG. 5 is stored. Specifically, the collision detection data table storage unit 84 stores collision detection data corresponding to each of the voice recognition device 1, the navigation device 2, the CD changer 3, and the audio device 4 connected to the bus 5. I have.

The frame collision judging section 86 extracts the data of the first byte of the frame transmitted and received on the bus 5, and extracts the data of the collision detecting data contained in the table stored in the collision detecting data table storage section 84. It is determined whether any one of them matches. If they do not match, the frame collision determination unit 86 instructs the reception data buffer 82 to discard the received frame.

The above-described collision detection data corresponds to additional data unique to the transmission source of the frame. Further, the transmission processing unit 66 provides the frame transmission unit with a frame collision determination unit 68,
86 corresponds to the collision detection means.

The navigation device 2 and the audio device 4 according to the present embodiment have the above-described configuration, and then the frame collision determination unit 68 included in the navigation device 2
The operation of the frame collision determination performed by the frame collision determination unit 86 included in the audio device 4 will be described.

FIG. 6 is a diagram showing a specific example of judging a frame collision, showing a case where a frame transmitted from the voice recognition device 1 and a frame transmitted from the navigation device 2 collide on the bus 5. I have. FIG. 6 (A)
FIG. 6 is a diagram showing a waveform of collision detection data added to the head of a frame transmitted from the voice recognition device 1;
FIG. 3B is a diagram illustrating a waveform of collision detection data added to the head of a frame transmitted from the navigation device 2. FIG. 6C shows a case where the collision detection data corresponding to the speech recognition device 1 shown in FIG. 6A and the collision detection data corresponding to the navigation device 2 shown in FIG. 6B collide. FIG. 3 is a diagram showing waveforms on a bus 5. In addition,
In the following description, when data “0” and “1” overlap due to data collision on the bus 5,
It is assumed that “0” has been set to have priority.

As shown in FIG. 6, when the collision detection data 01h corresponding to the speech recognition device 1 and the collision detection data 02h corresponding to the navigation device 2 collide, the bus 5
The above data is 00h.

Therefore, in the navigation device 2 which is the transmission source of the frame, when the frame is transmitted from the transmission processing unit 66, the data of the first 8 bits of the frame transmitted and received on the bus 5 corresponds to its own device. The frame collision can be detected by determining by the frame collision determination unit 68 whether the data coincides with the collision detection data 02h. In the above-described example, the data of the first 8 bits of the frame actually transmitted / received on the bus 5 is 00h, and the collision detection data of the own device is 02h, which does not match. Is determined to be in effect.

In the audio device 4, the data of the first 8 bits of the frame transmitted and received via the bus 5 matches any one of the collision detection data stored in the collision detection data table storage unit 84. The frame collision determination unit 86 determines whether or not a frame collision has occurred, so that a frame collision on the bus 5 can be detected. In the above-described example, the data of the first 8 bits of the frame actually transmitted / received on the bus 5 is 00h, and as shown in FIG. 5, any of the data stored in the collision detection data table storage unit 84. Since they do not match the data, it is determined that the frames collide on the bus 5.

As described above, in the data communication system according to the present embodiment, when the collision detection data having a unique value corresponding to each device connected to the bus 5 is set and the frame is transmitted and received between the devices, , The collision detection data is added to the beginning of the frame. In particular, the collision detection data described above is devised so that when frames collide with each other on the bus 5, the data does not match any of the collision detection data set corresponding to each device. Therefore, it is possible to easily and reliably detect that a frame has collided on the bus 5 only by checking the content of the collision detection data added to the head of the frame transmitted on the bus 5. Moreover, since the comparison processing of this portion can be realized by a program processing by a microcomputer or the like, the cost can be reduced as compared with a case where a collision of a frame is detected using a dedicated circuit.

In the above-described embodiment, the data length of the collision detection data is 8 bits. However, the data length is not limited to 8 bits. Can be set to the number of bits. Further, as described above, the number of bits whose logic is set to “1” when generating the collision detection data is not limited to one bit. It is possible to set in the range of ~ (M-1) bits.

In the above-described embodiment, when detecting a frame collision, the collision detection data set in advance and the collision detection data added to the frame actually transmitted and received on the bus 5 are compared. Although the collision of the frame on the bus 5 is determined by comparison, the logic state of each bit of the collision detection data added to the frame transmitted and received on the bus 5 is checked, and the logic is “1”. By counting the number of bits, the presence / absence of a frame collision on the bus 5 may be determined. That is, in the above-described example, when a frame collides on the bus 5, the number of bits whose logic is "1" always decreases, and this can be detected to determine the frame collision. . In particular, when the frame collision determination is performed in this manner, the collision detection data table storage unit 84 provided in the receiving-side apparatus to which the frame is to be transmitted becomes unnecessary, so that the processing and configuration are simplified. Cost can be reduced.

The location where the collision detection data is added does not necessarily have to be at the beginning of the frame, but can be added at any predetermined location in the frame. Further, in the above-described embodiment, the case where the frame is transmitted from the navigation device 2 to the audio device 4 has been described as an example. However, on the contrary, the case where the frame is transmitted from the audio device 4 to the navigation device 2 or
The present invention can be applied to the case where frames are transmitted and received between other devices.

[Second Embodiment] Since the data transmission unit 22 in each device connected to the bus 5 has the frame end determination unit 70, transmission is started at different timings. A plurality of frames do not collide on the bus 5. However, after the frame end determination unit 70 actually determines the end of the frame, the transmission timing of the frame from the transmission processing unit 66 may be slightly shifted. In such a case, a change point of the waveform on the bus 5 may substantially coincide with the sampling timing of the device on the receiving side, so that it may not be possible to accurately detect a frame collision on the bus 5. .

FIG. 7 is a diagram showing a specific example of collision detection data used in the second embodiment. The data for collision detection according to the present embodiment is designed so that even if the data for collision detection collides with each other, the contents always change before and after the collision.

More specifically, when considering the start bit and parity added before and after each collision detection data is converted into serial data, the logic is "1".
And the bit whose logic is “0” are 2
It is set to be continuous for more than bits. Therefore, as the data for collision detection, 1Eh, 66h, 78
h, 86h, 98h and E0h.

By using such collision detection data, the transmission timing of the two frames becomes approximately 1.5.
Even if the time is shifted up to the time corresponding to the bit, the frame collision can be reliably detected by examining the data of the first 8 bits.

FIG. 8 is a diagram showing the correspondence between the devices connected to the bus 5 and the collision detection data of the present embodiment. As shown in FIG. 8, in the present embodiment, among the above-described six patterns of collision detection data, 78h is assigned to the voice recognition device 1, 86h is assigned to the navigation device 2, and 98h is assigned to the navigation device 2.
h corresponds to the audio device 4 and E0h corresponds to the CD changer 3, respectively. Note that the collision detection data table storage unit 84 included in the audio device 4 stores a table corresponding to the collision detection data list shown in FIG.

The data communication system of the present embodiment transmits and receives frames using the collision detection data as shown in FIGS. 7 and 8 described above. Next, a specific example of frame collision detection will be described. explain.

FIG. 9 is a diagram showing a specific example of a frame collision in the second embodiment. 9A is a signal waveform showing 98h which is collision detection data corresponding to the audio device 4, and FIG. 9B is a signal waveform showing 86h which is collision detection data corresponding to the navigation device 2. It is a waveform. For example, a case where the transmission start timing of two frames is shifted by about 1.3 bits is shown. FIG. 9C shows the signal waveforms shown in FIG.
The signal waveform shown in (B) is a waveform that has collided on the bus 5.

In each device connected to the bus 5, the sampling timing is set in synchronization with the frame previously transmitted to the bus 5. For example, as indicated by an arrow in FIG. 9C, the sampling timing is set so that data is taken in for each bit at a timing shifted by 0.5 bit from the transmission start timing of the frame. For this reason, in each device connected to the bus 5, the data extracted from the waveform on the bus 5 shown in FIG. 9C is "00001000" in binary notation, which is "08h" in hexadecimal notation. , It does not match any of the collision detection data corresponding to each device. Therefore, the frame collision determination unit 68 or 86 can determine the collision of the frame on the bus 5.

In particular, in the present embodiment, since the collision detection data is set so that the logic of each successive bit in units of two bits from the beginning including the start bit is the same, up to about 1.5 bits Even if the transmission timing is shifted within the range, the collision of the frames can be reliably detected. For example, as shown by “*” in FIG.
Of the two bits set to the same logic, the value of the four bits whose transmission timing is later,
Even if the transmission timing of one frame is shifted, the same logic as in the case where the transmission timing is not shifted at all is obtained. Therefore, by examining the contents of these four bits, it is possible to reliably detect a frame collision.

The data for collision detection in the above-described second embodiment includes a high-level period and a low level when considering the start bit and parity added before and after the data is converted to serial data. Although the data is set so that the level period is continuous for 2 bits or more, the period for which the high level and the low level are continuous may be 3 bits or more or 4 bits or more. By setting such that three or more bits are continuous, it becomes possible to detect a collision of frames whose transmission timings are shifted within a range up to about 2.5 bits. Further, by setting such that four or more bits are continuous, it becomes possible to detect a collision of frames whose transmission timing is shifted within a range up to about 3.5 bits.

[0053]

As described above, according to the present invention, by transmitting a frame by adding unique additional data to each transmission source, when these additional data collide with each other on a communication channel, the data is always transmitted. Since a part of the content can be destroyed, it is possible to reliably detect that the frames have collided. In addition, since it is only necessary to detect the collision of the frame, it is not necessary to use a dedicated circuit by hardware, and the cost of parts and the like can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of a data communication system according to a first embodiment.

FIG. 2 is a diagram showing a detailed configuration of a navigation device and an audio device.

FIG. 3 is a diagram illustrating a data structure of a frame generated by a transmission data generation unit.

FIG. 4 is a diagram for explaining a frame to which collision detection data is added.

FIG. 5 is a diagram showing an example of collision detection data.

FIG. 6 is a diagram showing a specific example of determining a frame collision.

FIG. 7 is a diagram showing a specific example of collision detection data used in the second embodiment.

FIG. 8 is a diagram showing the correspondence between each device connected to a bus and the collision detection data of the present embodiment.

FIG. 9 is a diagram illustrating a specific example of a frame collision according to the second embodiment.

[Description of Signs] 1 Voice recognition device 2 Navigation device 3 CD changer 4 Audio device 64 Start data setting unit 66 Transmission processing unit 68, 86 Frame collision determination unit 70 Frame end determination unit 80 Reception processing unit 84 Storage of data table for collision detection Department

Claims (4)

[Claims] In a data communication system in which transmission of a frame is permitted on the condition that there is no frame transmitted on a communication path, additional data unique to a transmission source of the frame is added to the frame and transmitted to the communication path. 1. A data communication method, comprising: a frame transmitting unit that performs frame transmission; and a collision detecting unit that detects a collision of a frame on the communication channel based on the content of the additional data transmitted to the communication channel. 2. The apparatus according to claim 1, wherein the collision detecting means provided at the transmission source of the frame detects a collision of the frame when additional data having a content different from that of the additional data transmitted by itself is detected. Characteristic data communication system. 3. The frame according to claim 1, wherein the collision detecting means provided at a transmission destination of the frame is configured such that the additional data corresponding to the frame received via the communication path is the additional data unique to the transmission source of the frame. A data communication method characterized in that a frame collision is detected when the frame collision is not included in the list. 4. The transmission / reception of a frame performed through the communication path in the form of serial data according to claim 1 or 2, wherein a plurality of consecutive bits are set to the same content in the additional data. A data communication method characterized by the following.