JP3785291B2 - Data communication method - Google Patents

Description

[0001]
BACKGROUND 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]
[Prior art]
Conventionally, in asynchronous communication in which a plurality of data communication devices perform data communication using a single communication medium, data is transmitted from two or more data communication devices at the same time. There was a case where the destruction of. When the data is destroyed, the contents of the transmitted / received data are changed. Therefore, it is necessary to detect that a data collision has occurred in the transmission source device or the transmission destination device.
[0003]
There are two typical ones for detecting destruction due to data collision. The first is a method of providing a dedicated detection circuit for detecting data collision on the communication path. For example, if each bit data of “0” and “1” collides on the communication path, “0” is preferentially transmitted. In this detection circuit provided in each transmission source device, When the data “1” sent by the client changes to “0” on the communication path, it is determined that the data sent by itself collides with the data sent by another transmission source. Since a dedicated detection circuit is used, a 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]
The second method is to continue sending data even if data collides on the communication path, and to detect data destroyed by the collision. For example, data corruption can be detected by examining the CRC code in the data and the contents of parity added in byte units.
[0005]
[Problems to be solved by the invention]
By the way, in the method of detecting data collision using the above-described dedicated circuit, special hardware is required for data collision detection, which raises a problem of increasing costs. In addition, when using a general-purpose microcomputer for communication (hereinafter referred to as “microcomputer”), there are many cases where the above-described collision detection circuit is not provided. There is also a risk of losing freedom.
[0006]
In addition, in the method of detecting data collision by examining the contents of data using a CRC code or the like, a correct CRC code may be obtained accidentally even though the data is destroyed due to collision. Data collisions could not be detected.
[0007]
The present invention was created in view of the above points, and an object of the present invention is to provide a data communication method capable of reliably detecting a collision of data on a communication path without using dedicated hardware. There is.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, in the data communication method of the present invention, when transmission of a frame is allowed on the condition that there is no frame transmitted on the communication path, additional data specific to the transmission source of the frame is added. The frame 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 content 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 path, a part of the contents is always destroyed, so that it is possible to reliably detect that the frames collide with each other. it can. In addition, since it is only necessary to be able to detect the collision of frames, it is not necessary to use a dedicated circuit by hardware in particular, and the cost of components and the like can be reduced.
[0009]
Further, it is desirable that the collision detection means provided at the frame transmission source detect 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 sent by itself needs to be compared, the processing can be simplified.
[0010]
Further, the collision detection means provided in the frame transmission destination is configured such that the additional data corresponding to the frame received via the communication path is not included in the list of additional data specific to the frame transmission source. It is desirable to detect frame collisions. By providing additional data of each transmission source as a list and using this as a comparison target, it is possible to reliably detect frame collisions.
[0011]
In addition, when the transmission / reception of the frame performed via the communication path is performed in the form of serial data, it is desirable that the above-described additional data is set to have the same content in a plurality of consecutive bits. Even when the transmission timing of a frame transmitted on the communication path is deviated, the collision of frames can be reliably detected as long as it is within a range of continuous bits.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a data communication system according to an embodiment to which the present invention is applied will be described with reference to the drawings.
[0013]
[First Embodiment]
FIG. 1 is a diagram illustrating an overall configuration of a data communication system according to the first embodiment. The data communication system according to this 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.
[0014]
The voice recognition device 1 performs voice recognition processing on the operation voice generated by the user's voice, and the recognition result is sent to other devices such as the navigation device 2 and the audio device 4 by data communication via the bus 5. It is done. The navigation device 2 detects the position of the host vehicle and displays a map around the position of the host vehicle, searches for a route to the destination selected by the user, performs route guidance, and the like.
[0015]
The CD changer 3 is loaded with a plurality of CDs, reads a signal recorded on the recording surface of the CD selected by the user, and reproduces music or the like. The audio device 4 is an all-in-one type audio device included in a single housing housed in a dashboard in a vehicle interior, and includes, for example, an operation panel having various operation keys in addition to a radio tuner and a cassette tape deck. Yes. Various operation instructions performed using the operation panel are performed on the CD changer 3, the voice recognition device 1, and the like in addition to those performed on 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 via the bus 5 by data communication.
[0016]
Next, a 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 showing a detailed configuration of the navigation device 2 and the audio device 4.
[0017]
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 predetermined navigation operations such as display processing of a map image around the vehicle position, route search processing, route guidance processing, and the like. For example, the audio device 4 performs voice guidance during route guidance. A frame indicating a voice interrupt request to be transmitted is output to the data transmission unit 22. The data transmission unit 22 is for converting the data output from the navigation processing unit 20 into a communication format and transmitting it to another device. The transmission data generation unit 60, the transmission data buffer 62, the head The data setting unit 64, the transmission processing unit 66, the frame collision determination unit 68, and the frame end determination unit 70 are configured.
[0018]
The transmission data generation unit 60 generates a frame by adding various data necessary for data communication to the transmission data output from the navigation processing unit 20.
[0019]
FIG. 3 is a diagram illustrating a data structure of a frame generated by the transmission data generation unit 60. As shown in FIG. 3, the frame is composed of a communication type (TYPE), a transmission destination address (DA), a transmission source address (SA), a data length (LEN), transmission data (DATA), and error detection data (in order from the top). ERR).
[0020]
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 designated. The transmission destination address stores an address corresponding to the device that is the transmission destination of this frame. The transmission source address stores an address corresponding to the device that is the transmission source of this frame. In the present embodiment, an address corresponding to the audio device 4 is stored in the transmission destination address, and an address corresponding to the navigation device 2 is stored in the transmission source address.
[0021]
The data length represents the data length of data to be transmitted (DATA shown in FIG. 3) in bytes. As the transmission data, data to be transmitted is stored, and for example, data indicating a voice interrupt request output from the navigation processing unit 20 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, CRC code, or the like is used.
[0022]
The transmission data buffer 62 temporarily stores frames generated by the transmission data generation unit 60. The head data setting unit 64 adds 1-byte “collision detection data” having a predetermined content set to detect a frame collision on the bus 5 to the frame.
[0023]
FIG. 4 is a diagram for explaining a frame to which collision detection data is added. As shown in FIG. 4, 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. The collision detection data uses a unique value for each device connected to the bus 5, and when a frame collision occurs on the bus 5, the collision actually sent onto the bus 5. By checking the contents of the detection data, frame collision is determined.
[0024]
Next, the content of the above-described collision detection data will be specifically described. FIG. 5 is a diagram illustrating an example of collision detection data. In this 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, as the content of the collision detection data, as shown in FIG. 5, eight patterns of 01h, 02h, 04h, 08h, 10h, 20h, 40h, and 80h are conceivable. Note that “h” added to the above-described collision detection data represents a hexadecimal number. In the present embodiment, the eight patterns of collision detection data described above are associated with each device connected to the bus 5. Specifically, as shown in FIG. 5, for example, 01h corresponds to the speech 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.
[0025]
The transmission processing unit 66 reads the frame (the frame after the collision detection data is added) stored in the transmission data buffer 62 in byte units, converts it into serial data, and further sets a start bit “0” at the head, Parity (for example, even parity) and stop bit “1” are respectively added to the rear part, and the result is transmitted onto the bus 5.
[0026]
The frame collision determination unit 68 extracts data for the first byte of the frame transmitted / received on the bus 5, and matches the content of the collision detection data added to the first byte of the frame output from the transmission processing unit 66. It is determined whether or not. If they do not match, the frame collision determination unit 68 instructs the transmission processing unit 66 to retransmit the frame.
[0027]
The frame end determination unit 70 determines the end of a frame transmitted / received on the bus 5 and outputs a frame signal. For example, a high-level frame signal is output after a predetermined time has elapsed since there is no data transmitted / received on the bus 5. This frame signal is used as a signal for permitting the transmission operation by the transmission processing unit 66. That is, the transmission processing unit 66 transmits a frame on the condition that a frame signal is output from the frame end determination unit 70, that is, on the condition that there is no frame transmitted on the bus 5 at that time.
[0028]
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 other devices, and includes a reception processing unit 80, a reception data buffer 82, a collision detection data table storage unit 84, a frame collision determination. A portion 86 is included.
[0029]
When a frame is input in the form of serial data, the reception processing unit 80 extracts data in units of 1 byte by detecting a start bit and a stop bit (if parity is included, an error due to parity is further generated. After the check), this data is sequentially converted into parallel data to restore the frame shown in FIG. Then, after performing error detection processing using the error detection data included in this frame, various data other than the transmission destination address and error detection data included in the frame are output to the reception data buffer 82 To do.
[0030]
The reception data buffer 82 temporarily stores various data output from the reception processing unit 80. 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.
[0031]
The collision detection data table storage unit 84 stores a table corresponding to the list of collision detection data shown in FIG. 5 described above. Specifically, the collision detection data table storage unit 84 stores collision detection data corresponding to each of the speech recognition device 1, the navigation device 2, the CD changer 3, and the audio device 4 connected to the bus 5. Yes.
[0032]
The frame collision determination unit 86 extracts the data of the first byte of the frame transmitted / received on the bus 5 and matches one of the collision detection data included in the table stored in the collision detection data table storage unit 84. Determine whether you are doing it. If they do not match, the frame collision determination unit 86 instructs the reception data buffer 82 to discard the received frame.
[0033]
The collision detection data described above corresponds to additional data unique to the frame transmission source. The transmission processing unit 66 corresponds to the frame transmission unit, and the frame collision determination units 68 and 86 correspond to the collision detection unit.
[0034]
The navigation device 2 and the audio device 4 of the present embodiment have the above-described configuration. Next, the frame performed in the frame collision determination unit 68 included in the navigation device 2 and the frame collision determination unit 86 included in the audio device 4. The collision determination operation will be described.
[0035]
FIG. 6 is a diagram showing a specific example of determining a frame collision, and shows a case where a frame transmitted from the speech recognition apparatus 1 and a frame transmitted from the navigation apparatus 2 collide on the bus 5. FIG. 6A is a diagram illustrating a waveform of collision detection data added to the head of a frame transmitted from the speech recognition apparatus 1, and FIG. 6B is a diagram illustrating a frame transmitted from the navigation apparatus 2. It is a figure which shows the waveform of the data for collision detection added to the head. FIG. 6C shows a case where the collision detection data corresponding to the speech recognition apparatus 1 shown in FIG. 6A and the collision detection data corresponding to the navigation apparatus 2 shown in FIG. 6B collide. FIG. 6 is a diagram showing waveforms on the bus 5. In the following description, it is assumed that when data “0” and “1” overlap due to data collision on the bus 5, “0” is set to have priority. To do.
[0036]
As shown in FIG. 6, when the collision detection data 01h corresponding to the voice recognition device 1 and the collision detection data 02h corresponding to the navigation device 2 collide, the data on the bus 5 becomes 00h.
[0037]
Therefore, in the navigation device 2 that is the transmission source of the frame, when the frame is transmitted from the transmission processing unit 66, the data for the first 8 bits of the frame transmitted / received on the bus 5 is the collision detection corresponding to the own device. A frame collision can be detected by determining whether the frame data 02h matches the frame data by the frame collision determination unit 68. In the above-described example, the data for 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 and does not match. It is determined that
[0038]
Also, in the audio device 4, whether the data for the first 8 bits of the frame transmitted / received via the bus 5 matches any of the collision detection data stored in the collision detection data table storage unit 84. By determining this by the frame collision determination unit 86, a frame collision on the bus 5 can be detected. In the above-described example, the data for the first 8 bits of the frame actually transmitted / received on the bus 5 is 00h, and any of the data stored in the collision detection data table storage unit 84 as shown in FIG. Since the data does not match, it is determined that the frames collide on the bus 5.
[0039]
Thus, in the data communication system of the present embodiment, when collision detection data having a unique value corresponding to each device connected to the bus 5 is set and frames are transmitted and received between the devices, This collision detection data is added to the head of the frame. In particular, the above-described collision detection data is devised so that it does not coincide with any of the collision detection data set corresponding to each device when frames collide on the bus 5. Therefore, it is possible to easily and surely detect that a frame has collided on the bus 5 only by examining the content of the collision detection data added to the head of the frame sent onto the bus 5. In addition, since this part of the comparison process can be realized by a program process using a microcomputer or the like, the cost can be reduced as compared with the case where a collision of frames is detected using a dedicated circuit.
[0040]
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, and a desired number of bits according to the communication format to be used. Can be set to Further, as described above, the number of bits for which the logic is “1” when generating the collision detection data is not limited to 1 bit, but is 1 for the data length M bits of the collision detection data. It is possible to set in a range of ~ (M-1) bits.
[0041]
Further, in the above-described embodiment, when detecting a frame collision, the collision detection data set in advance is compared with the collision detection data added to the frame actually transmitted / received on the bus 5. Although the collision of the frame on the bus 5 is determined, the logical state of each bit of the collision detection data added to the frame transmitted / received on the bus 5 is checked, and the number of bits whose logic is “1” is determined. By counting, the presence or absence of a frame collision on the bus 5 may be determined. In other words, in the above-described example, when the frames collide on the bus 5, the number of bits for which the logic is “1” always decreases, so that this can be detected to determine the collision of the frames. . In particular, when frame collision determination is performed in this way, the collision detection data table storage unit 84 provided in the reception-side apparatus that is the frame transmission destination is not necessary, so that the processing and configuration are simplified. The cost can be reduced.
[0042]
Further, the location where the collision detection data is added does not necessarily need to be at the head of the frame, and can be added to any predetermined location in the frame. In the above-described embodiment, the case where a frame is transmitted from the navigation device 2 to the audio device 4 has been described as an example, but conversely, the case where a frame is transmitted from the audio device 4 to the navigation device 2 or the like. The present invention can also be applied to transmission / reception of frames between these devices.
[0043]
[Second Embodiment]
By the way, since the data transmission unit 22 in each apparatus connected to the bus 5 includes the frame end determination unit 70, a plurality of frames whose transmission is started at different timing collide on the bus 5. There is nothing. However, there may be a case where the transmission timing of the frame from the transmission processing unit 66 is slightly shifted after the frame end determination unit 70 actually determines the end of the frame. In such a case, there may be a case where the waveform change point on the bus 5 and the sampling timing in the receiving-side apparatus are substantially coincident with each other. Therefore, there is a possibility that the frame collision on the bus 5 cannot be accurately detected. .
[0044]
FIG. 7 is a diagram illustrating a specific example of collision detection data used in the second embodiment. The collision detection data of this embodiment is considered so that the contents always change before and after the collision even when the collision detection data collide with each other.
[0045]
Specifically, when the start bit and parity added before and after the collision detection data are converted into serial data are considered, the logic is “1” and the logic is “0”. Are set so that 2 bits or more are consecutive. Therefore, 6 patterns of 1Eh, 66h, 78h, 86h, 98h, and E0h are considered as collision detection data.
[0046]
By using such collision detection data, even if the transmission timing of the two frames is shifted to a time corresponding to approximately 1.5 bits, the frame data can be obtained by examining the data for the first 8 bits. Can be reliably detected.
[0047]
FIG. 8 is a diagram illustrating a correspondence relationship between each device connected to the bus 5 and the collision detection data according to the present embodiment. As shown in FIG. 8, in this embodiment, among the six patterns of collision detection data described above, 78h is the voice recognition device 1, 86h is the navigation device 2, 98h is the audio device 4, and E0h is Each corresponds to the CD changer 3. The collision detection data table storage unit 84 included in the audio device 4 stores a table corresponding to the list of collision detection data shown in FIG.
[0048]
The data communication system of this embodiment performs frame transmission / reception 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.
[0049]
FIG. 9 is a diagram illustrating a specific example of a frame collision in the second embodiment. 9A is a signal waveform indicating 98h which is collision detection data corresponding to the audio device 4, and FIG. 9B is a signal waveform indicating 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 is a waveform in which the signal waveform shown in FIG. 9A and the signal waveform shown in FIG. 9B collide on the bus 5.
[0050]
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 captured for each bit at a timing shifted by 0.5 bits from the frame transmission start timing. 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 representation, and “08h” in hexadecimal representation. Therefore, it can be seen that the data does not match any collision detection data corresponding to each device. Therefore, the frame collision determination unit 68 or 86 can determine a frame collision on the bus 5.
[0051]
In particular, in this embodiment, since the collision detection data is set so that the logic of each successive bit including the start bit in units of 2 bits is the same, the range of up to about 1.5 bits is set. Even if the transmission timing is deviated, it is possible to reliably detect a frame collision. For example, as indicated by “*” in FIG. 7, the transmission timing of two frames on the bus 5 is shifted with respect to the 4-bit value of the later transmission timing of 2 bits set to the same logic. Even if it is a case, it has the same logic as the case where transmission timing does not shift at all. Therefore, by checking the contents of these 4 bits, it is possible to reliably detect a frame collision.
[0052]
Note that the collision detection data in the second embodiment described above has a high level period and a low level period when the start bit and parity added before and after conversion to serial data are considered. Although the data is set to be continuous for 2 bits or more, the period in which the high level and the low level are continuous may be 3 bits or more or 4 bits or more. By setting the bits to be continuous for 3 bits or more, it becomes possible to detect a collision of frames whose transmission timings are shifted within a range up to about 2.5 bits. In addition, by setting 4 bits or more to continue, it is possible to detect a collision of frames whose transmission timings are shifted within a range up to about 3.5 bits.
[0053]
【The invention's effect】
As described above, according to the present invention, a frame is transmitted by adding specific additional data to each transmission source, so that when the additional data collides on the communication path, a part of the content is always included. Since it can be destroyed, it is possible to reliably detect that the frames collide with each other. In addition, since it is only necessary to be able to detect the collision of frames, it is not necessary to use a dedicated circuit by hardware in particular, and the cost of components 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 illustrating an example of collision detection data.
FIG. 6 is a diagram illustrating a specific example of determining a frame collision.
FIG. 7 is a diagram illustrating a specific example of collision detection data used in the second embodiment.
FIG. 8 is a diagram illustrating a correspondence relationship between each device connected to a bus and collision detection data according to the present embodiment.
FIG. 9 is a diagram illustrating a specific example of a frame collision in the second embodiment.
[Explanation of symbols]
1 Voice recognition device
2 Navigation device
3 CD changer
4 Audio equipment
64 Lead data setting section
66 Transmission processing unit
68, 86 Frame collision determination unit
70 Frame end determination unit
80 Reception processing section
84 Data table storage for collision detection

Claims (3)

In a data communication method in which transmission of a frame is allowed on condition that there is no frame transmitted on the communication path,
Frame transmission means for adding additional data specific to the frame transmission source to the frame and sending it to the communication path;
A collision detection means for detecting a collision of frames on the communication path based on the content of the additional data sent to the communication path;
The provided, transmission and reception of frames are performed via the communication path is performed in the form of serial data, data communication method the additional data, wherein Rukoto plurality consecutive bits are set to the same contents. In claim 1,
The data communication system according to claim 1, wherein the collision detection means provided at a frame transmission source detects a collision of frames when additional data having a content different from that of the additional data transmitted by itself is detected. In claim 1,
The collision detection means provided at the transmission destination of the frame does not include 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. A data communication method characterized by detecting a collision of frames sometimes.

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