JPH0946280A - Method for judging connecting state of communication line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for judging the connecting state of communication lines by means of a communication system attaining cost down by using a transmitter-receiver capable of alternatively switching a transmission mode or a reception mode. SOLUTION: A check command is transmitted from a master computer 1 to N-number of slave computers 2-1 to 2-N connected with an optical coupler 9 through optical communication equipments 5, 5-1 to 5-N capable of alternatively switching the transmission mode or the reception mode through optical fibers 7. The computers 2-1 to 2-N judges the state of a line to the computer 1, based on the check command and transmits an answer signal. The computer 1, communicates data between with the computers 2-1 to 2-N only for prescribed period. Then the computer 1 repeats polling consisting of the process like this and judges the state of the line to the computers 2-1 to 2-N, based on the polling result of at least one time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a communication line connection state determining method for performing 1: N (N is an integer of 2 or more) half-duplex communication using a single communication line.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of the configuration of a device that performs 1: 1 half-duplex communication between computers installed over a long distance. In FIG. 3, 1 is a master computer and 2 is a slave computer. The input / output terminal of the master computer 1 is connected to one input / output terminal of the communication device 3, and the input / output terminal of the slave computer 2 is connected to one input / output terminal of the communication device 3 '. The other input / output terminals of the communication device 3 and the communication device 3'are respectively connected to the ends of the communication line 4, which is a single-core optical cable or coaxial cable.

The communication device 3 comprises a transmitter 3a, a receiver 3b, a code decision device 3c, and a coupler 3d. The transmitter 3a outputs the output signal from the master computer 1 to C
MI (Coded Mark Inversion) modulation and communication line 4
Is transmitted to the communication line 4 after being subjected to modulation suitable for the transmission characteristics of. Further, the receiver 3b receives a signal transmitted via the communication line 4, CMI demodulates the received signal, and outputs the signal to the master computer 1. The code determiner 3c detects a CMI error and a CD (Carrier Detect) error of the signal received by the receiver 3b,
The detection result is output to the master computer 1. The coupler 3d demultiplexes the signal transmitted via the one-core communication line 4 and sends it to the receiver 3b, or sends the transmission signal of the transmitter 3a to the one-core communication line 4. Further, the communication device 3'has the same configuration as the communication device 3, and each component has the same function as that of the communication device 3.

In the above configuration, the master computer 1
When the data is output to the communication device 3, the transmitter 3a in the communication device 3 performs CMI modulation on the data and sends the data to the communication line 4. Then, the communication device 3 ′ receives the transmitted data by the receiver 3b ′, performs CMI demodulation, and outputs the data to the slave computer 2. Similarly, when the slave computer 2 outputs data to the communication device 3 '
The transmitter 3a 'therein performs CMI modulation and sends it out to the communication line 4, and the communication device 3 receives the signal transmitted from the communication line 4 at the receiver 3b, performs CMI demodulation and outputs it to the master computer 1. .

While communication is being performed between the master computer 1 and the slave computer 2, the receivers 3b, 3
b ′ constantly monitors the line, and when the transmitter 3a is transmitting data, the communication device 3 ′ prohibits the transmitter 3a ′ from transmitting data. Conversely, when the transmitter 3a 'is sending data, the communication device 3 prohibits the transmitter 3a from transmitting data. By thus preventing the transmitters 3a and 3a 'from transmitting data at the same time, half-duplex communication is realized between the master computer 1 and the slave computer 2. The code determiners 3c and 3c ′ constantly monitor the output signals of the receivers 3b and 3b ′,
When a CMI error or a CD error is detected, the master computer 1 and the slave computer 2 respectively
To output a CMI error signal or a CD error signal.

In the CMI modulation described above, modulation and demodulation are performed with a simple circuit configuration, an error is detected in the content of the CMI modulation signal, and the duty of the power is 50% in principle, so AGC (automatic gain control) ) Is a modulation method used when performing long-distance communication. Hereinafter, the CMI modulation described above will be described with reference to FIG. FIG. 4 is a timing chart showing the principle of CMI modulation and CMI demodulation. In FIG. 4, it is assumed that time has passed from left to right. Further, "data" in FIG. 4 is output from the master computer 1 and the slave computer 2 in FIG. 3 to the communication devices 3 and 3'in FIG. 3, respectively.

The transmitters 3a and 3a 'shown in FIG. 3 perform "modulation" on the "data" by the following method with a reference cycle from the rising edge of the transmission clock to the next rising edge. That is,
When the data is "0", modulation is performed so that the first half cycle is "1" and the second half cycle is "0", and CMI output is performed. If the data is "1", the logic ("1" or "0") of the CMI output when the data of "1" was previously modulated is stored, and the logic of the CMI output this time is that logic. Modulation is performed so that the logic becomes complementary to. Also, FIG.
The transmitters 3a and 3a 'therein modulate the CMI output in accordance with the transmission characteristics of the communication line 4 in FIG. 3 as shown in the "in-fiber modulation waveform" described in FIG. That is, the transmitter 2
a and 2a ′ are 1 when the CMI modulated signal has a logic of 1.
When the CMI signal has a logic of 0 for a pulse signal of 0.6 MHz, it is modulated and output to a pulse signal of 10.8 MHz.

Next, the CMI demodulation method will be described. When the above-mentioned pulse signal is transmitted from the communication line 4 in FIG. 3, the receivers 3b and 3b ′ in FIG.
The input clock is obtained and the reception clock is extracted. And
The receivers 3b and 3b 'perform CMI demodulation with the reference period from the fall of the received clock to the next fall. That is, the fall of the CMI input is detected at the fall of the reception clock, and this fall is detected.
The demodulated signal for a period is set to "0". Otherwise, that is, when the logic of the CMI signal does not change at the fall of the reception clock, the demodulated signal for one cycle is set to "1". In this way, demodulation of the CMI input is performed.

In the following, the above-mentioned CMI error, C
The D error will be described. Code determiner 3c in FIG.
3c ′ is the receiver 3 in FIG. 3 with the reference cycle from the rising edge of the reception clock to the next rising edge.
The output signals of b and 3b 'are monitored. According to the coding rule of CMI modulation, when the logic of the CMI input changes within the reference period, that is, when the original data is "0", the CMI
The input always changes from "1" to "0". When the logic does not change within the reference period, that is, when the original data is "1", the CMI input is a logic complementary to the logic when the logic did not change the previous time. When the two coding rules described above are violated, the code decision machines 3c and 3c ′ are not required to use the CMI.
An error is detected and a CMI error signal is output to the master computer 1 and the slave computer 2 in FIG. 3, respectively. In addition, the CMI output and the CMI input are not characterized by the same logic for longer than 1.5 cycles.
Therefore, the code determiners 3c and 3c 'store the logic of the CMI input every half cycle of the reception clock and sequentially compare four consecutive logics. If all four logics are the same, a CD error is output to the master computer 1 and the slave computer 2, respectively.

As described above, in the configuration shown in FIG. 3, the communication device 3 including the transmitters 3a and 3a ', the receivers 3b and 3b', the code decision devices 3c and 3c ', and the couplers 3d and 3d'. , 3'is used to realize 1: 1 half-duplex communication between the master computer 1 and the slave computer 2.

[0011]

By the way, between one master computer and N slave computers:
When performing N communication, one communication device described above is required on the master computer side and N communication devices are required on the slave computer side. However, when N is large, arranging N communication devices has a drawback that the cost becomes extremely high. The present invention has been made in view of the above points, and achieves cost reduction of a communication system by using a transmitting / receiving means capable of selectively switching a transmission mode and a reception mode, and in the communication system, a master computer and a slave computer are provided. It is an object of the present invention to provide a method for determining the connection state of a communication line that can realize the 1: N half-duplex communication between the communication line and the communication line and further determine the connection state of a plurality of communication lines.

[0012]

According to the present invention, one master computer that functions as a master and N (N is an integer of 2 or more) slave computers that function as slaves of the master computer are set in a transmission mode and a reception mode. 1 via a transmission / reception means capable of switching modes selectively
A method for determining a connection state of a communication line in a communication system in which data is communicated between the master computer and the slave computer by connecting a core wire to a communication network having a 1: N branch, The first step of transmitting a preset check command to the slave computer, and the master computer waits for a reply signal from the slave computer, and the slave computer transmits the check command transmitted from the master computer. A second step of judging the state of the line to the master computer based on the judgment result and transmitting the reply signal corresponding to the judgment result to the master computer, and presetting between the master computer and the slave computer. Data communication only during the specified period And a third step, repeatedly performs the polling made from the first step to third step, at least with respect to the slave computer 1
A method for determining a connection state of a communication line is characterized in that the state of a line to the slave computer is determined based on the result of polling of the number of times.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention are based on the technical ideas described below. That is,
One master computer that functions as a master and N that functions as a slave of the master computer (N is 2
In a 1: N communication system that communicates with (the above integer) slave computers, the cost of the communication system is reduced by using a communication device having a transmission / reception element. And, it means to realize 1: N half-duplex communication in this communication system. An embodiment of the present invention based on the above technical idea will be described with reference to the drawings. FIG. 2 is a block diagram showing a schematic configuration of a communication system to which the method for determining the connection state of the communication line of the present invention is applied. In this figure, the same parts as those in FIG. Is omitted. In the following description, it is assumed that a plurality of devices and the reference numerals of the components of the devices are attached with supplementary reference numerals to identify them.

In FIG. 2, reference numeral 5 is an optical communication device, which is an LD.
(Laser diode) 5a, LD driver 5b, and amplifier circuit 5c. The LD 5a is an element capable of selectively switching between the transmission mode and the reception mode. The LD driver 5b performs CMI modulation on data and drives the LD 5a described above, and is controlled by the master computer 1. The amplifier circuit 5c amplifies the signal received by the LD 5a and performs CMI demodulation,
This is a circuit for detecting a CMI error and a CD error, and these received signals and error signals are transmitted to the master computer 1.
Is output to The optical communication device 5 and the optical communication devices 5-1 to 5-1
5-N has exactly the same configuration. Reference numeral 6 is an optical coupler formed by branching a one-core optical cable into 1: N. An optical fiber communication line 7 connects the optical coupler 6 and the optical communication devices 5 and 5-1 to 5-N. An optical communication device 5 is connected to one end of the optical coupler 6 via a communication line 7.
A master computer 1 is connected to the. Further, optical communication devices 5-1 to 5-N are respectively connected to the other N terminal ends via a communication line 7, and the optical communication devices 5-1 to 5-1 are connected.
Slave computers 2-1 to 2-N are connected to 5-N.

FIG. 1 is a flowchart showing a communication method for realizing 1: N half-duplex communication in the communication system shown in FIG. In this figure and FIG. 2, N = 10 and master computer 1 and slave computers 2-1 to 2-1.
It is assumed that the 2-10 performs 1:10 communication.
In FIG. 1, in step S1, an array F of 1 row and 10 columns that stores the connection states of the slave computers 2-1 to 2-10 is initialized, and all the elements of this array F are initialized to "0". Be converted. This array F is secured in the master computer 1, and the element of the array is "0" when the connection state of the communication line 7 is normal, and "1" when it is abnormal.
Becomes The variable n is the slave computer 2-1 to 2-1.
2-10 is a variable that specifies any one, and its initial value is set to 1. As a result, communication is first performed between the master computer 1 and the slave computer 2-1.

In step S2, the master computer 1
Sends a check command to the slave computer 2-1. Next, in step S3, it is determined whether or not the answer to the check command sent in step S2 has been received. If an answer is received,
Proceed to step S4. In step S4, since the line is normal, the master computer 1 stores the state. That is, since the current value of the variable n is 1, the array F
The element in the first row, first column of is 0. Further, in step S3 described above, if the answer is not received, the process proceeds to step S5, and it is determined whether a timeout has occurred. For this time-out period, for example, 1
6 msec is set. If it is determined in step 5 that the timeout has not occurred, the process proceeds to step S3.
Proceed to and it is determined whether an answer has been received. That is, in step S3 and step S5, when the answer is not received, the process of waiting for the answer is performed for 16 msec.

If it is determined in step S5 that the timeout has occurred, the process proceeds to step S6, and it is determined whether the element in the first row, first column of the array F is "1".
If this element is not "1", the process proceeds to step S7. In step S7, the master computer 1 stores that the line is abnormal. That is, the element in the first row, first column of the array F becomes "1". If the element in the first row, first column of the array F is “1” in step S6 described above, the process proceeds to step S8. In step S8, the master computer 1 determines that the line has not been established with the first slave computer.

After step S4 described above, the process proceeds to step S9 to determine whether or not the master computer 1 has data to be sent to the slave computer 2-1. If there is data to be sent, the process proceeds to step S10. In step S10, a data transmission time (160 msec) for transmitting data from the master computer 1 to the slave computer 2-1 is set, and asynchronous half-duplex communication is performed between the master computer 1 and the slave computer 2-1. This data transmission time is 160m
The reason for setting sec is to secure an effective data transfer rate. If there is no data to be sent in step S9, after step S7 and step S8
After, the process proceeds to step S11. Step S11
Then, the same time (160 msec) as the data communication time described in step S10 is set as the waiting time. During this time, the master computer 1 and the slave computer 2-1 interrupt the processing and measure the transmission / reception timing. . Step S10 and step S described above
After step 11, the process proceeds to step S12, and it is compared whether or not the value of the variable n is 10, and if the variable n is not equal to 10, the process proceeds to step S13. In step S13, the value of the variable n is incremented and the process returns to step S2. When the value of the variable n is 10 in step S12 described above, the process proceeds to step S14, "1" is assigned to the variable n, and the master computer 1
Becomes the slave computer 2-1 again.
Then, the process returns to step S2.

As described above, polling is always repeated, and the master computer 1 determines the connection state of the line based on the results of the two polls. That is, when the previous polling result is "1" and the current polling result is "0", the process proceeds from step S3 to step S4, and it is determined that the previous polling result is abnormal. Regardless, slave computer 2-
It is determined that there is a line for 1. Also, when the previous polling result is "0" and the current polling result is "1", the process proceeds from step S6 to step S7, and it is determined that there is a line to the slave computer 2-1. However, if the previous polling result is "1" and the current polling result is also "1", the process proceeds from step S6 to step S8, and it is determined that there is no line to the slave computer 2-1.

Further, one cycle of the above-mentioned polling is 160 msec × 10 = 1.6 seconds when all the slave computers 2-1 to 2-10 have normal lines. The longest response time of any of 2-1 to 2-10 is approximately 1.6 seconds × 10 msec × 3 = 4.8 seconds. For example, assuming that the master computer 1 communicates with the slave computer 2-1, immediately after the answer from the slave computer 2-1 is received, the slave computer 2-1 and the optical communication device 5-are immediately connected. It is assumed that the connection with 1 is broken. In this case, the line is judged to be normal according to the result of the first polling, and the line is judged to be abnormal when the second polling is completed. But,
Since the result of the first polling out of the two polling results is normal, the master computer 1 determines that the connection is established and performs the third polling. At the time when the third polling is completed, it is determined that both the previous polling result and the current polling result are line abnormalities, so the master computer 1 determines that the slave computer 2-1 is not connected. The response time is the time from the last data communication to the next communication.
The longest response time at this time is the time from the last data communication until it is determined that there is no line.
Therefore, the longest response time is about three polling times.

The check command transmitted from the master computer 1 to the slave computers 2-1 to 2-10 is transmitted at a minimum period of 1.6 seconds and at a maximum period of 1.76 seconds. Therefore, the slave computers 2-1 to 2-10 determine that there is no line if the next check command is not sent within 1.5 cycles, that is, 2.4 seconds after the check command is sent. In addition,
The above communication method can be used for checking the line after the optical fiber construction work and for determining the presence or absence of the line deterioration or the line failure. Further, the communication method is not limited to the optical communication, and a coaxial cable or the like can be used. It is also applicable to the used telecommunications.

[0022]

As described above, in the method for determining the connection state of the communication line according to the present invention, the transmitting / receiving means capable of selectively switching the transmission mode and the reception mode is used,
Since the mode of the transmitting / receiving means is switched according to a predetermined procedure, 1: N half-duplex communication is possible between one master computer and N slave computers in a communication system for cost reduction. There is an effect that. Further, the master computer repeatedly polls the slave computer, and determines the state of the line to the slave computer based on the result of polling the slave computer at least once. As a result, it is possible to determine the connection state of the plurality of communication lines. Further, since the slave computer determines the state of the line to the master computer based on the check command transmitted from the master computer, the slave computer can determine the connection state of the communication line. effective.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method for realizing 1: N half-duplex communication according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a communication system to which the communication line connection state determination method of the present invention is applied.

FIG. 3 is a diagram illustrating a case where a long-distance computer according to the related art has a 1:
FIG. 3 is a block diagram showing a configuration example of a device that performs half-duplex communication of No. 1.

FIG. 4 is a timing chart showing the principle of CMI modulation and CMI demodulation.

[Explanation of symbols]

1 ... Master computer, 2-1, 2-2, 2-N ... Slave computer, 5-1, 5-2, 5-N ... Optical communication device, 5-1a, 5-2a, 5-Na ... LD ( Laser diode), 6 ... Coupler

Claims (1)

[Claims] 1. A transmission mode and a reception mode can be selectively switched between one master computer functioning as a master and N (N is an integer of 2 or more) slave computers functioning as slaves of the master computer. A method for determining a connection state of a communication line in a communication system in which data is communicated between the master computer and the slave computer by connecting one core wire to a communication network having a 1: N branch through various transmission / reception means. And a first step of transmitting a preset check command from the master computer to the slave computer, the master computer waiting for a reply signal from the slave computer, and the slave computer transmitting from the master computer. Based on the check command that has been The second step of determining the state of the line to the master computer and transmitting the reply signal corresponding to the determination result to the master computer, and the preset process between the master computer and the slave computer The third that carries out data communication only for a certain period
And repeatedly determining the state of the line to the slave computer based on at least one polling result of the slave computer. And a method for determining a connection state of a communication line.