JP2004328624A - Data communication device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the collision of data while suppressing power consumption and reducing costs of respective terminals. <P>SOLUTION: When a transmitting packet is sent on a channel 1, a packet transmitting part 11 sends the transmitting packet of which the data are added with header information including information for the collision detection of a specified code volume in which own address information and all code values are set to 1 or 0, and the packet transmitting part 11 receives it. A packet comparator 17 compares the address information of the transmitted packet and the address information of the received packet, and compares the collision detection information of the transmitted packet and the collision detection information of the received packet. As a result, if both the collision detection information do not agree, it is discriminated that data collision occurs on the communication channel 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data communication apparatus and method for transmitting and receiving data in a multi-drop type communication system by a step synchronization method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as techniques for avoiding data loss due to data competition or collision during data communication and suppressing a decrease in throughput, polling of a transmission control method and CSMA / CD of an access method in a LAN (Local Area Network) have been known. (Carrier Sense Multiple Access / Collision Detection) and CSMA / ACK are known.
[0003]
Polling is a transmission control method in which, when a plurality of terminals share a communication line, a host provided on a network inquires whether or not each terminal has a transmission request.
[0004]
CSMA / CD is used as an access method of Ethernet (registered trademark), and converts a digital signal output from a serial controller of a terminal into a Manchester code method or the like by a code conversion circuit and sends the data to a communication line. In this method, a collision detection circuit monitors whether a data collision has occurred. When the data collision is detected by the collision detection circuit, the data transmission of the terminal that transmitted the data is stopped, and the data is transmitted again after a randomly set waiting time.
[0005]
Further, the CSMA / ACK does not detect data collision itself, and returns an ACK signal to the data transmission side when data is correctly received at the data reception side. This is a method of recognizing collision.
[0006]
As a conventional data communication system, for example, a technology described in Patent Document 1 below is known. This data communication method uses a start-stop synchronization method at the time of data communication. When the communication path becomes idle, data transmission is performed, and then the transmitted data is received, and the transmitted data and the received data are transmitted. Compare words. When there is no mismatch between the two data, it is determined that no data collision has occurred in the communication path. When both data do not match, a data collision has occurred in the communication path. Is determined.
[0007]
[Patent Document 1]
Japanese Patent Publication No. 6-71262
[Problems to be solved by the invention]
However, in a data communication system employing polling, even when no transmission request is issued to any terminal, the host inquires whether a transmission request has been issued for each terminal. Will be consumed extra.
[0009]
In a data communication system employing CSMA / CD, it is necessary to implement hardware such as a code conversion circuit and a collision detection circuit, and it is difficult to reduce the cost of each terminal.
[0010]
Further, in a data communication system employing CSMA / ACK, it is not necessary to implement hardware called a collision detection circuit, but even if a collision occurs and the sign is inverted, data is transmitted from the data transmission side. Since transmission is continued, there is a problem that corrupted data occupies a communication path for a long time.
[0011]
Furthermore, the data communication system described in Patent Document 1 requires a circuit for monitoring whether a communication path is idle or not, and requires hardware cost as in the case of the CSMA / CD. Therefore, it is difficult to reduce the cost of each terminal.
[0012]
Therefore, the present invention has been proposed in view of the above-described circumstances, and provides a data communication device and method capable of detecting data collision while suppressing power consumption and cost of each terminal. The purpose is to:
[0013]
[Means for Solving the Problems]
The present invention relates to a data communication device that shares a communication line with another data communication device, sends serial data to the communication line, and receives serial data from the communication line. Then, a transmission packet is generated by adding header information storing collision detection information of a predetermined code amount in which its own address information and all code values are set to 1 or 0 from the head position of the packet to the data. Then, the transmitting means performs a communication synchronization process on the generated transmission packet in code units and transmits the packet.
[0014]
As a result, the transmission packet is sent out to the communication line, and becomes ready for reception by the receiving means. Then, in the data communication device, when the transmission packet transmitted from the transmission unit is received by the reception unit, the data collision detection unit compares the address information included in the transmission packet transmitted from the transmission unit with the transmission packet received by the reception unit. In addition to comparing the address information included therein, the collision detection information included in the transmission packet transmitted from the transmission unit is compared with the collision detection information included in the transmission packet received by the reception unit.
[0015]
As a result, the data communication device determines that a data collision has occurred on the communication line when the two address information do not match or the two collision detection information do not match, and The above-mentioned problem is solved by stopping transmission of transmission packets from the communication line to the communication line.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
For example, as shown in FIG. 1, in a multi-drop type data communication system, the present invention relates to a data communication terminal 2A and a data communication terminal 2B (hereinafter, simply referred to as "data communication terminals") that share a communication path 1 which is a serial bus. Terminal 2 ").
[0018]
[Configuration of Data Communication Terminal 2]
The data communication terminal 2 includes a packet transmission unit 11 and a packet reception unit 12 connected to the communication path 1 as shown in FIG. In this data communication terminal 2, when transmitting data to another data communication terminal 2, a packet is transmitted from the packet transmission unit 11 to the communication path 1, and a packet from the other data communication terminal 2 is transmitted via the communication path 1. When sent, the data is received by the packet receiving unit 12.
[0019]
Further, the data communication terminal 2 includes a data processing unit 13 that performs processing for generating data to be transmitted and various types of information processing on the received data. When data to be transmitted (transmission data) occurs, the data processing unit 13 stores the transmission data in the transmission buffer 14. As a result, the packet transmission unit 11 creates a transmission packet in which header information and the like are added to the transmission data stored in the transmission buffer 14, and transmits the transmission packet to the communication path 1. On the other hand, when the transmission packet is transmitted from the communication path 1 to the packet receiving unit 12, the data communication terminal 2 interprets the header information and the like by the packet transmitting unit 11 and receives the transmission packet. Stores the transmission packet as a reception packet in the reception buffer 15, reads out the reception data stored in the reception buffer 15 by the data processing unit 13, and performs various processes.
[0020]
The packet transmitting unit 11 operates in an asynchronous system in which synchronization is determined in code units (1 bit units), and transmits a transmission packet to the communication path 1 as serial data. Further, when a transmission packet is transmitted, the packet receiving unit 12 operates in a start-stop synchronization method that determines synchronization in code units (1 bit units), and receives a transmission packet of serial data.
[0021]
That is, the packet transmitting unit 11 and the packet receiving unit 12 add a start bit having a code value of “0” to the beginning of 1-byte data and a stop bit having a code value of “1” at the end of the 1-byte data. Is added. As a result, the packet transmitting unit 11 and the packet receiving unit 12 synchronize the serial data transmission and reception with reference to the start bit and the stop bit.
[0022]
In addition, the packet transmission unit 11 and the packet reception unit 12 in this example set the code value to “0”, set the low (Low) level value, and set the code value to “1”, set the code value to “High”. Serial data is generated as an NRZ (NonReturn-to-Zero) code as a level value. When a data collision occurs between the serial data of the NRZ code and other serial data on the communication channel 1, the code value is usually likely to be “0”.
[0023]
In the data communication terminal 2, the NRZ code transmitted / received as serial data may be any code that can uniquely determine the code value “1” or “0” from only the value detected during a certain sampling time. , A double-flow NRZ code or a single-flow NRZ code.
[0024]
Further, the data communication terminal 2 includes a transmission timing measuring unit 16 that monitors whether data transmission is being performed on the communication channel 1 in order to control the transmission timing of the packet transmitting unit 11. The transmission timing measurement unit 16 detects that no transmission packet has been sent to the packet reception unit 12, and when it is determined that data transmission has not been performed on the communication channel 1, 1 is notified that transmission of a transmission packet is possible.
[0025]
Furthermore, the data communication terminal 2 includes a packet comparison unit 17 that compares a transmission packet transmitted from the packet transmission unit 11 with a reception packet transmitted from the packet transmission unit 11 and received by the packet reception unit 12. . In the packet comparison unit 17, the transmission packet transmitted from the packet transmission unit 11 and stored in the transmission buffer 14 and the reception packet received by the packet reception unit 12 and stored in the reception buffer 15. The received packet is read and compared in code units. As a result, the packet comparing unit 17 determines whether or not the transmission packet and the reception packet match, and determines whether or not a packet collision has occurred in the communication path 1.
[0026]
[Data collision detection processing by data communication terminal 2]
Next, a data collision detection process for detecting a data collision in the communication path 1 in the data communication terminal 2 configured as described above will be described with reference to the flowchart in FIG.
[0027]
First, in the data communication terminal 2, in the packet transmission unit 11, the transmission timing is measured by the transmission timing measurement unit 16 (step S1). When it is determined that communication is not currently performed (step S2), the transmission packet is transmitted. By transmitting (step S3), a transmission packet is transmitted at a transmission timing when data transmission is not performed on the communication channel 1. When the transmission of the transmission packet is started, the packet transmission unit 11 continues to transmit the transmission packet until transmission data to be transmitted ends.
[0028]
The packet transmission unit 11 reads transmission data from the transmission buffer 14 in units of 1 bit, and transmits data at a timing when other data communication terminals 2 are not transmitting data. 1, the data collision occurs when another data communication terminal 2 transmits a transmission packet at exactly the same transmission timing, or when another data communication terminal 2 transmits another packet immediately before reading the first 1-byte transmission data for packet transmission. Only when the terminal 2 starts packet transmission.
[0029]
As a result, data in which data collision occurs in the communication channel 1 is within 2 bytes from the head even if the processing time for reading data is taken into consideration. When data collision occurs in the communication channel 1 as described above, the data communication terminal 2 stops the packet transmission of the packet transmission unit 11.
[0030]
In order to stop the packet transmission of the packet transmission unit 11 when the data collision occurs, the packet transmission unit 11 transmits the collision detection information for detecting the data collision in the header area of the transmission packet in step S3. Add. Then, in the data communication terminal 2, after transmitting the transmission packet to which the collision detection information is added to the communication path 1, the transmission packet is received by the packet receiving unit 12 (step S4). At this time, the packet receiving unit 12 stores the transmission packet including the collision detection information as a reception packet in the reception buffer 15 by detecting that the own address information is stored in the header area.
[0031]
In such a state, the transmission buffer 14 stores a transmission packet in which the collision detection information is stored in the header area, and the reception buffer 15 stores a reception packet in which the collision detection information is stored in the header area. . The packet comparing unit 17 compares the collision detection information included in the header area of the transmission packet stored in the transmission buffer 14 with the collision detection information included in the header area of the reception packet stored in the reception buffer 15. The comparison is performed in code units (1 bit units) (step S5).
[0032]
The packet comparing unit 17 determines whether or not the collision detection information of the transmission packet and the collision detection information of the reception packet match (step S6). Determines that no data collision has occurred in the communication path 1 (step S7), and causes the packet transmission unit 11 to continue packet transmission. On the other hand, when the packet comparing unit 17 determines that the two pieces of collision detection information do not match, it determines that a data collision has occurred in the communication channel 1 (step S8). Stop sending packets.
[0033]
[Specific example of data collision detection processing]
Next, the specific content of the data collision detection processing in the data communication terminal 2 as described above will be described.
[0034]
"First data collision detection processing"
First, a description will be given of a first data collision detection process when the own address information included in the header area is used as collision detection information.
[0035]
In the first data collision detection process, the packet transmission unit 11 adds its own unique address information to the beginning of a transmission packet. Then, as shown in FIG. 4, the process of transmitting the serial data with the code value “0101010101” from the data communication terminal 2A and the process of transmitting the serial data with the code value “0101010001” from the data communication terminal 2B are started simultaneously. In this case, a data collision occurs in the communication channel 1, and the serial data transmitted from the data communication terminal 2A changes from the code value “0101010101” to the code value “0010101001”.
[0036]
Then, the data communication terminal 2A compares the code value “0101010101” of the transmission packet with the code value “0010101001” of the received packet by the packet comparing unit 17, and determines that the code values are different. Detects that a data collision has occurred.
[0037]
In response, data communication terminal 2A stops data transmission after detecting a stop bit after transmitting the address information.
[0038]
Thereby, in the data communication terminal 2A, when the serial data having the code value “1” and the serial data having the code value “0” collide, even if the code value becomes “0”, the difference between the code values becomes smaller. It is possible to detect that a data collision has occurred even if data transmission is started simultaneously with no difference in time for one bit from the data communication terminal 2B.
[0039]
Therefore, according to the data communication terminal 2, it is possible to suppress the power consumption as compared with a case where data collision is avoided by performing polling, for example. Further, according to the data communication terminal 2, there is no need to mount hardware such as a code conversion circuit and a collision detection circuit, and the cost of the terminal can be reduced.
[0040]
"Second data collision detection process"
Next, following the own address information included in the header area, 1-byte data with all code values set to “1” is added, and the 1-byte data with all code values set to “1” collides. A description will be given of the second data collision detection process in the case of the detection information.
[0041]
In the second data collision detection processing, the packet transmission unit 11 detects the collision at the beginning of the transmission packet following the unique address information of its own and the code value of the data between the start bit and the stop bit is all “1”. Information is added.
[0042]
Then, as shown in FIG. 5, when the data communication terminal 2A performs a process of transmitting the serial data of the code value “0111111111” following the address information of the code value “0101010101”, the data communication terminal 2A It is assumed that the data communication terminal 2B starts transmitting serial data when transmitting the eye data. Then, the serial data transmitted from the data communication terminal 2A collides with the serial data transmitted from the data communication terminal 2B, and the code value of the serial data received by the data communication terminal 2A is "010101010101111111111". In such a state, the data communication terminal 2A cannot detect a data collision only by comparing the contents of the address information, but the code value is changed from “1” to “0” at the third bit of the collision detection information. , The data comparison unit 17 can detect a data collision.
[0043]
In response, data communication terminal 2A stops data transmission after detecting the stop bit after transmitting the collision detection information. On the other hand, the data communication terminal 2B continues packet transmission because there is no mismatch between the collision detection information included in the transmission packet and the collision detection information included in the received packet.
[0044]
Therefore, according to the data communication terminal 2A, even if the data communication terminal 2B starts packet transmission at slightly different time and a data collision occurs with a shift of several bits, it is detected that the data collision has occurred. can do.
[0045]
Further, according to the data communication terminal 2, the case where another data communication terminal 2 starts packet transmission immediately before reading the first 1-byte transmission data for packet transmission, and the processing time for data reading is reduced. Considering this, the data in which the data collision occurs is within 2 bytes from the beginning, but it is necessary to detect the data collision reliably within the 2 bytes and stop the packet transmission without completing the transmission of all transmission data. Can be.
[0046]
"Third data collision detection processing"
Next, 1-byte data with all code values being "1" is added to the address information included in the header area, followed by 1-byte data with all code values being "0". The third data collision detection process in the case where the one-byte data whose all code values are “1” and the one-byte data whose all code values are “0” are used as the collision detection information will be described.
[0047]
In the third data collision detection process, the packet transmission unit 11 places, at the beginning of a transmission packet, data having a code value of all data “1” between the start bit and the stop bit, following its own unique address information. Collision detection information consisting of data in which the code value of the data between the start bit and the stop bit is all “0” is added.
[0048]
Then, as shown in FIG. 6, after performing a process of transmitting serial data having a code value of “0111111111000000001” following address information having a code value “0101010101” from the data communication terminal 2A, the data communication terminal 2B transmits Suppose you start sending. Then, the serial data transmitted from the data communication terminal 2A collides with the serial data transmitted from the data communication terminal 2B, and the code value of the serial data received by the data communication terminal 2A is “010101010101101111111110100000001”. In such a state, the data communication terminal 2A cannot detect the data collision only by comparing the contents of the address information, but the code value is changed from “0” to “1” at the third bit of the collision detection information. , The data comparison unit 17 can detect a data collision.
[0049]
On the other hand, in the serial data received by the data communication terminal 2B, the code value of the collision detection information following the address information is “01111111101”. In such a state, the data communication terminal 2B cannot detect a data collision only by comparing the contents of the address information, but the code value is changed from “0” to “1” by the start bit of the collision detection information. , The data comparison unit 17 can detect a data collision.
[0050]
Thereby, the data communication terminal 2A stops the packet transmission after transmitting the collision detection information having the code value of all “0”, and the data communication terminal 2B transmits the operation input signal having the code value of all “1”. Stop sending packets.
[0051]
Therefore, according to the data communication terminal 2, even if the code value after data collision does not always become “0” when packet transmission is started simultaneously or with a slight time difference from two or more terminals, Data collision can be reliably detected by adding the collision detection information whose code values are all “0”.
[0052]
That is, according to the data communication terminal 2, either the case where the code value is inverted from “1” to “0” due to the data collision, or the case where the code value is inverted from “0” to “1” due to the data collision. Even in this case, it is possible to reliably detect data collision. Further, according to the data communication terminal 2, for example, when a data collision occurs in which serial data with code values “0”, “1”, and “1” are transmitted from three terminals, the code value is changed to “ Even if it changes from "0" to "1", a data collision can be reliably detected.
[0053]
Further, according to the data communication terminal 2, when transmitting serial data by the double-flow NRZ method, the collision detection information in which the code values are all “1” and the code values in which the code values are all “0” are transmitted after the address information. Since the collision detection information is transmitted, the data collision is detected by the collision detection information having all the code values “1” by utilizing the possibility that the code value becomes “0” when a data collision occurs. Data collision can be detected in a short time.
[0054]
In the third data collision detection process, a case has been described in which, after address information, collision detection information having code values of all “1” and collision detection information having code values of all “0” are transmitted. If there is a high possibility that the code value becomes “1” when a data collision occurs, collision detection information having code values of “0” is allotted following the address information, and then the code value becomes “1”. The collision detection information “1” may be provided. Thus, the data communication terminal 2 can more efficiently detect a data collision.
[0055]
In the second data collision detection processing, the third data collision detection processing, and the data collision detection processing shown in FIG. 7, the transmission packet transmitted from the data communication terminal 2A and the transmission packet transmitted from the data communication terminal 2B are Even when the data collision occurs, since the data received by the data communication terminal 2B has no error, the data communication terminal 2B continues the packet transmission. Even in such a case, the data communication terminal 2B can normally continue the packet transmission by stopping the packet transmission by the data communication terminal 2A.
[0056]
Note that the above embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and other than the present embodiment, various modifications may be made according to the design and the like within a range not departing from the technical idea according to the present invention. Can be changed.
[0057]
【The invention's effect】
According to the present invention, the collision detection information included in the transmission packet transmitted from the transmission unit is compared with the collision detection information included in the transmission packet received by the reception unit, and both pieces of collision detection information are compared. If not, it can be determined that data collision has occurred in the communication line, so that power consumption can be suppressed as compared to a case where data collision is avoided by performing polling, for example.
[0058]
Further, according to the present invention, it is not necessary to implement hardware such as a code conversion circuit and a collision detection circuit, and the cost of the terminal can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a state where a plurality of data communication terminals to which the present invention is applied are connected to a common communication path.
FIG. 2 is a block diagram showing a functional configuration of a data communication terminal to which the present invention has been applied.
FIG. 3 is a flowchart showing a processing procedure of a data collision detection process by the data communication terminal to which the present invention is applied.
FIG. 4 is a diagram illustrating a change in a code value when a collision occurs in serial data transmitted from a plurality of data communication terminals, illustrating a first data collision detection process by the data communication terminal to which the present invention is applied; FIG.
FIG. 5 is another diagram showing a change in code value when a collision occurs in serial data transmitted from a plurality of data communication terminals, and illustrates a second data collision detection process by the data communication terminal to which the present invention is applied. It is a figure for explaining.
FIG. 6 is a still further diagram showing a change in a code value when a collision occurs in serial data transmitted from a plurality of data communication terminals, the third data collision detection processing by the data communication terminal to which the present invention is applied; FIG.
FIG. 7 is a still further diagram showing a change in a code value when a collision occurs in serial data transmitted from a plurality of data communication terminals, in which packet transmission is stopped by one data communication terminal and the other data is transmitted. FIG. 6 is a diagram for explaining that a communication terminal continues packet transmission.
[Explanation of symbols]
Reference Signs List 1 communication path 2 data communication terminal 11 packet transmission unit 12 packet reception unit 13 data processing unit 14 transmission buffer 15 reception buffer 16 transmission timing measurement unit 17 packet comparison unit

Claims (8)

A data communication device sharing a communication line with another data communication device, transmitting a serial data packet to the communication line, and receiving a serial data packet from the communication line.
From the head position of the packet, a transmission packet is created by adding header information storing collision detection information of a predetermined code amount in which its own address information and all code values are set to 1 or 0 are added to data, and communication is performed in code units. Transmitting means for performing a synchronous process and transmitting a transmission packet to the communication line;
Receiving means for receiving a transmission packet transmitted from the transmitting means;
The address information included in the transmission packet transmitted from the transmission unit is compared with the address information included in the transmission packet received by the reception unit, and the collision detection information included in the transmission packet transmitted from the transmission unit is compared with the address information. Comparing the collision detection information contained in the transmission packet received by the receiving means, and when both the address information do not match, or when both the collision detection information do not match, the communication line A data collision detecting means for determining that a data collision has occurred;
A data communication device, comprising: a communication control unit that stops transmission of a transmission packet from the transmission unit to the communication line when the data collision detection unit determines that a data collision has occurred. The transmission means, following its own address information, header information including 1-byte collision detection information in which all code values are set to 0 and 1-byte collision detection information in which all code values are set to 1 To the data to create a transmission packet and send it,
The data collision detection means includes two-byte collision detection information following the address information of the transmission packet transmitted from the transmission means, and two-byte collision detection information following the address information of the transmission packet received by the reception means. 2. The data communication apparatus according to claim 1, wherein data collision is detected by comparing information with information. The communication control means, if the data collision detection means determines that no data collision has occurred on the communication line, causes the transmission means to continue transmitting a transmission packet to the communication line. The data communication device according to claim 1 or 2, wherein 2. The data communication apparatus according to claim 1, wherein the transmitting unit transmits an NRZ code transmission packet as serial data to the communication line, and the receiving unit receives the NRZ code transmission packet as serial data. apparatus. When transmitting and receiving serial data packets by sharing a communication line with a plurality of data communication devices, a data communication method for detecting data collision of the communication line,
From the head position of the packet, a transmission packet is created by adding header information storing collision detection information of a predetermined code amount in which its own address information and all code values are set to 1 or 0 are added to data, and communication is performed in code units. Send a transmission packet to the communication line by performing a synchronization process,
Receiving the transmission packet;
The address information included in the transmitted transmission packet is compared with the address information included in the received transmission packet, the collision detection information included in the transmitted transmission packet, and the address information included in the received transmission packet are compared. Compare the collision detection information, if both address information does not match, or if both collision detection information does not match, it is determined that data collision has occurred in the communication line,
A data communication method comprising: stopping transmission of a transmission packet to the communication line when it is determined that the data collision has occurred. Subsequent to the address information, header information including 1-byte collision detection information in which all code values are set to 0 and 1-byte collision detection information in which all code values are set to 1 is added to the data. Create and send outgoing packets,
The two-byte collision detection information following the address information of the transmitted transmission packet is compared with the two-byte collision detection information following the address information of the received transmission packet. 6. The data communication method according to claim 5, wherein when the information does not match, a data collision of the communication line is detected. When data collision occurs in the communication line, the data communication device in which the two address information or the two collision detection information do not match stops sending a transmission packet to the communication line, 7. The data communication device according to claim 5, wherein a data communication device in which both address information or both of the collision detection information coincide with each other continues transmission of a transmission packet to the communication line. Method. When transmitting the transmission packet, serial data of an NRZ code is created and transmitted to the communication line, and when the transmission packet is received, the transmission packet of the NRZ code is received as serial data. 6. The data communication method according to 5.

Images