JPH10215273A - Method for discriminating position of broken loop in loop interface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the method that discriminates a position of broken loop on the occurrence of the broken loop in a loop interface in a communication system where a master station and a plurality of slave stations are connected in a loop. SOLUTION: A master station is provided with a timer A and each slave station is provided with a timer B respectively, a time of the timer A is set longer than a polling period and the timer A is started simultaneously at the transmission of each polling information (S1), and when a broken loop is detected by the expiration of the time (S5), the timers B whose times are set sequentially longer toward a direction of data communication are started (S6). When each slave station receives data from a preceding station before its timer B expires, the slave station adds its won slave station number to the data and sends the resulting data to a succeeding station and when the timer B expires before the reception of the data, the slave station sends a slave station number of its own to the succeeding station. The master station discriminates a position of a broken loop based on information including the slave station number from the final slave station of the loop.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of judging a break in a loop interface of a communication system in which a master station and a plurality of slave stations are connected in a loop.

[0002]

2. Description of the Related Art FIG. 8 is a diagram showing an example of the configuration of a communication system in which a plurality of stations are connected in a loop, and the system shown in the figure comprises one master station and a plurality of slave stations. In FIG. 8, the master station includes a CRT 1, a control unit 2, and a keyboard 3, and the slave stations A, B, C, and D have the same configuration. The terminals of each station are connected by connection cables 4 and 5, and each terminal performs data communication via the connection cable 4. The connection cable 4 is connected from the master station S (transmission end) to the slave station A R (reception end), and from the slave station A S to the slave station B.
, And finally a loop connection that returns from the slave station S at the final stage to the master station R.

The connection cable 5 is a transmission path for a control signal for controlling the turning on and off of the power of each terminal. When the power of the master station is turned on, the information is transmitted to the slave station A via the connection cable 5, The power of the slave station A is also turned on. Slave station A
Is transmitted to the slave station B via the connection cable 5, and the slave station B is similarly turned on. Similarly, the power-on information is transmitted to the slave stations C and D, and the power is turned on. Thus, by turning on the power of the master station, the power of all the slave stations is also turned on. In general, the connection cable 4, which is a transmission line for communication data, can be used up to about 1 km in total length, and each terminal is often used in a relatively distant layout. In some cases, the terminals are placed in different offices. Sometimes used.

FIGS. 9A and 9B are block diagrams showing hardware configurations of the master station and the slave stations in FIG. FIG.
11A, reference numeral 11 denotes a CPU, 12 denotes a CPU peripheral circuit, 13 denotes a memory, 14 denotes a display unit control circuit, 15 denotes a display unit, 16 denotes an input control circuit, 17 denotes an input unit, 18 denotes a communication control circuit, 19 Denotes a CPU bus, and the master station and the slave stations are constituted by 11 to 19 described above. The respective units except the display unit 15 and the input unit 17 are connected by a CPU bus 19,
11. With this configuration, data input by the operator is displayed on the display unit 15, and data is transmitted / received to / from each terminal via the communication control circuit 18. FIG.
2B is a block diagram of the communication control circuit of FIG. 1A, and the communication control circuit 18 includes a control circuit 21, a receiving element 22, and a drive element 23. Then, the serial data is received by the receiving element 22, data processing is performed by the control circuit 21, and the serial data is output by the drive element 23.

FIG. 10 is a time chart showing a communication sequence when the power of the system shown in FIG. 8 is turned on. The loop interface of the system shown in FIG. 8 communicates by a polling method, and data used for polling (data for inquiring each terminal whether there is a transmission request at regular intervals) is called a "token". The following will be described. FIG.
In the time chart of 0, after the power supply to the system is turned on, the master station outputs a token to the slave station A, and the slave station A receives the token and indicates that its own device is in an operable state (CNA in the figure). And sends the data to the slave station B. Upon receiving the token, the slave station B sends data to the slave station C with data (CNB in the figure) indicating that the own apparatus is operable. The slave station C and the slave station D perform the same operation. Finally, the master station sends the token sent by the master station and the data (P, CNA, CNB, CNC, CND)
To receive. Thus, the master station checks the state of the slave station after the power is turned on. After that, the master station performs a polling operation of sending a token at a fixed period, and the slave station sends data to the master station by adding the data to be sent to the token when there is data to be sent from its own device. .

FIG. 11 is a time chart showing an example of a data communication sequence from the master station to the slave station in the system shown in FIG. The master station of the system in FIG. 8 sends data to slave stations in a frame format. The symbols in the frame of FIG. 11 have the following meanings. BP: Indicates that data is added to the frame. ADB: Indicates the destination of the frame, and ADB indicates that the frame is addressed to the slave station B. ADM: Indicates the source device of the frame, AD
M indicates a frame transmitted by the master station. DATA: Indicates actual data to be processed. In the time chart of FIG. 11, it is assumed that the master station has transmitted a frame as shown to the slave station A. The slave station A analyzes the contents of the frame, determines that the frame is not addressed to itself, and sends the received frame to the slave station B as it is. The slave station B analyzes the content of the received frame, recognizes that the frame is addressed to the own apparatus, copies the data of the frame to the memory of the own apparatus, and sends the received frame to the slave station C as it is. The slave station C also recognizes that it is not a frame addressed to itself, and sends the received frame to the slave station D as it is. The slave station D also recognizes that the frame is not addressed to itself, and sends the received frame to the master station as it is. In this way, the master station performs required data communication with the slave station B.

FIG. 12 is a flowchart showing a communication control process of the master station in the system shown in FIG. 8. Numerical values following S in FIG. 8 indicate step numbers. In the flowchart of FIG. 12, after powering on the system (see S81), the master station starts its own timer (see S82) and sends a token to slave station A (see S83). Then, it is determined whether or not a token has been received from the slave station (see S84). If a token has been received (if the determination result in S84 is YES), it is determined whether or not data from the slave station has been added to the received token (see S85). Performs the analysis processing of the added data (see S86), and if the data is not added, proceeds to the next token output processing (see S87). If the result of the determination in S84 is NO (if no token has been received), it is determined whether or not the timer started in S82 has timed out (see S88). Returning to S84, if the time-out has occurred, the loop is interrupted and a recovery operation waits (see S89).

FIG. 13 is a flowchart showing the communication control processing of the slave station in the system shown in FIG. 8. Numerals following S in the figure show step numbers. In the flowchart of FIG. 13, after power-on to the system (see S91), each slave station starts its own timer (see S92),
It is determined whether or not a token has been received (see S93). If the token is received (if the determination result in S93 is YES), it is determined whether or not the received data is a frame addressed to the own device (refer to S94). Is copied to the memory in the apparatus (see S95), and the process proceeds to S96. If the frame is not the frame addressed to the own device, the process immediately proceeds to S96. In S96, the received frame is output as it is to the slave station next to the loop (see S96), and the next token waits (S9).
7). If the determination result of S93 is NO (if no token has been received), it is determined whether or not the timer of the own station started in S92 has timed out (S93).
98), if not timed out, S
Returning to 93, if the time-out has occurred, the loop is broken and the token waits (see S99).

[0009]

FIG. 14 is a diagram showing an example of a failure in the loop interface of the system shown in FIG.
In FIG. 14, the connection cable 4 between the slave station B and the slave station C is broken. In this state, the polling token transmitted from the master station is transmitted only to the slave station B, and the token does not return to the master station. In this case, both the master station and the slave stations determine that an abnormality has occurred in the loop interface due to the timeout of the token wait in the communication control processing of FIGS. 13 and 14, display a message indicating that the abnormality has been detected, and confirm with the operator. Prompt. The operator needs to check the wiring of each terminal device and the operation of each terminal device to investigate the cause of this interface abnormality.
When the terminal devices are installed separately from each other, there is a problem that the work of searching for the cause of the abnormality takes a considerable amount of time.

[0010]

According to the present invention, there is provided a loop interface determining method for a loop interface in which a master station and a plurality of slave stations are connected in a loop, and polling information is transmitted from the master station to each slave station at predetermined intervals. A method for determining a loop break point of a loop interface in a system for performing data communication between a master station and a slave station and between slave stations, wherein a first and a second timer are provided for the master station and each slave station, The first timer has its value set to be longer than the transmission cycle of the polling information, and is started at the same time as the transmission of the polling information. The second timer is started after the detection of the loop break, and the timer value in each slave station is set according to the communication direction of data communication. Each slave station is set so as to be the next long time. When the slave station receives the slave station number from the preceding slave station in the communication direction before the timeout of the second timer, the slave station number of its own apparatus is included in the received information. The added information is transmitted to the next slave in the communication direction, and the timeout is used to transmit the slave number of the own device to the next slave in the communication direction, and the master station can receive from the last slave station in the communication direction. The loop break point is determined based on information including one or more slave station numbers. As a result, when a loop break occurs in the loop interface, it is possible to clearly determine which part of the loop interface is normal and which part is not normal, thereby improving the efficiency of the operator's work of searching for the cause of the failure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a flowchart showing a communication control process of a master station according to Embodiment 1 of the present invention. Numerical values following S in FIG. 1 indicate step numbers. The configuration of the communication system and the hardware configurations of the master station and the slave stations according to the first embodiment are shown in FIGS.
Is similar to The flowchart of FIG. 1 will be described. In S1 of FIG. 1, the timer A is started, and in S2, the token is sent to the slave station A. In S3, it is monitored that the token sent in S2 returns around the loop interface, and it is determined whether or not the token has been received. If a token has been received, the process proceeds to S4; otherwise, the process proceeds to S5.

In S4 of FIG. 1, it is determined whether or not data from a slave station has been added to the token. If data has been added, analysis processing of the added data is performed in S10. If the data from the slave station has not been added, the process returns to S1 to output the next token. If the token has not been received in S3, it is determined in S5 whether the timer A has timed out. Here, the value of the timer A is set to a time longer than the cycle of the token periodically transmitted from the master station in the normal operation state. Therefore, when the timer A times out, it means that the loop interface has a failure such as a break in the loop, and the token sent from the master station does not return after going around the loop. If the result of the determination in S5 is not a timeout, the process returns to S3 to monitor the reception of the token. If the result of the determination in S5 is a timeout, the process proceeds to S6 and the next timer B is started. Here, after the value of timer B is once broken,
The time is set to be longer than the time until data is sent from the slave station. Therefore, it is considered that there is no data transmitted from the slave station to the master station after the timer B times out.

In S7 of FIG. 1, it is determined whether or not data has been received from a slave station. If data has been received, the process proceeds to S8.
Then, the received data is analyzed to recognize the slave station that sent the data. Thereafter, the process proceeds to S9, and based on the recognition result in S8, the normally connected slave station and the abnormal slave station are displayed on the display unit to prompt the operator to confirm. If the result of determination in S7 is that data has not been received from the slave station,
At 11, it is determined whether or not the timer B has timed out. If not, the process returns to S7 to confirm whether or not data has been received from the slave station. If the result of the determination in S11 has timed out, the process proceeds to S9 and proceeds to S7.
A slave station determined to be not normal based on the determination result of S11 and S11 is displayed on the display unit to prompt the operator to confirm.

FIG. 2 is a flowchart showing a communication control process of the slave station according to the first embodiment of the present invention. Numerical values following S in FIG. 2 indicate step numbers. FIG. 2 shows a communication control process of the slave stations A, B, C, and D of the communication system. The flowchart of FIG. 2 will be described below. In S21 of FIG. 2, the timer A is started, and in S22, it is determined whether a token has been received. S23 when the token is received
The analysis of the received frame is performed to determine whether or not the frame is addressed to the own device. If the frame is addressed to the own device, the flow advances to S24 to copy the frame addressed to the own device to the memory in the device. Then, the flow advances to S25, and the received frame is directly sent to the next slave station (the slave station D is Station). If it is determined in S23 that the frame is not addressed to the own device, the process proceeds to S25, and returns to S21 to wait for the next token.

If it is determined in S22 that the token has not been received, the process proceeds to S26, where it is determined whether or not the timer A has timed out.
Return to step 22 to check whether the token has been received. Here, similarly to the case of the main station, the value of the timer A is set to be longer than the period of the token periodically transmitted from the main station in the normal state. If the result of the determination in S26 is a timeout, the process proceeds to S27, and the timer B is started. Here, the value of the timer B of each slave station is set in advance to a time longer than the time until the slave station number is transmitted from all the slave stations after detecting the loop break in S26. The timer values B ₁ , B ₂ , B ₃ , and B _{4 at} each of the slave stations A, B, C, and D are set to B ₁ <B ₂ <B ₃ <B ₄ so that the timer values B ₁ , B ₂ , B ₃ , and B ₄ sequentially become different values depending on the communication direction.
Are respectively set so that

After S27, the process proceeds to S28, in which it is determined whether or not data has been received from the slave station before the loop. If data has been received, the process proceeds to S29, where the slave data of the own apparatus is added to the received data. In addition, the data is sent to the next slave station in the loop. After that, in S30, it is displayed on the display unit that the terminal device has detected the loop break, and the operation waits for a recovery operation by the operator.

If it is determined in S28 that data has not been received from the slave station before the loop, the flow advances to S31 to determine whether or not the timer B has timed out. To check if data is received from the slave station at the preceding stage of the loop. S3
If it is determined that the time-out has occurred at 1, the processing proceeds to S
Proceed to 32 to send the slave station number of the own device to the slave station next to the loop. Thereafter, the process proceeds to S30, and waits for a loop break recovery operation.

FIG. 3 is a sequence diagram showing a communication operation example of the master station and the slave station when the loop is broken according to the first embodiment of the present invention. The master station and the slave station perform the communication control processing of FIGS. 1 and 2, respectively. By performing the above operation, if an interface disconnection accident occurs between the slave station B and the slave station C as shown in FIG. 14, the operation is performed as shown in FIG. Hereinafter, the operation of FIG. 3 will be described. When power is supplied to the system, the master station sends a token (indicated by P in the figure) to the slave station A. Upon receiving the token, the slave station A adds data (indicated by CNA in the figure) indicating that the own device is operable to the token (P), and sends a frame to the slave station B. The slave station B also adds data (indicated by CNB in the figure) indicating that the own device is in an operable state to the reception data (P, CNA), and
Send the frame to

However, since there is a disconnection between the slave stations B and C, the slave station C does not receive the frames (P, CNA, CNB). Therefore, the token is not returned to the main station via the communication route indicated by the broken line in the figure, and the main station detects the timeout of the timer A after the elapse of the set time of the timer A (indicated by XX seconds in the figure). By detecting the timeout of the timer A, the master station determines that the loop has been broken, and does not output the next token, and waits for data from the slave station. Thereafter, the slave station A times out the timer B ₁ and sends the slave station A's slave station number (shown by A in the figure) to the slave station B. When the slave station B receives the slave station number (A) from the slave station A, it adds the slave station number of the slave station B (shown by B in the figure) and sends it to the slave station C. (A, B) is not received. The slave station B after the timeout of the timer A, but sends a further time out of the timer B ₂ of the own station when the slave station slave station number of B (B) in the slave station C, the slave station C is also not received.

After the timer A times out, the slave station C sends its slave station number (shown by C in the figure) to the slave station D when the timer of its own station B ₃ further times out. The slave station D receives it from the slave station C, adds the slave station number of its own device, and sends the data to the master station (indicated by C and D in the figure). The master station analyzes the data received from the slave stations and determines a normally connected slave station and an abnormal slave station.
In the example of FIG. 3, since the slave station numbers of the slave stations C and D have been sent, it is determined that a failure has occurred before the preceding stage of the receiving circuit of the slave station C. By this determination, the master station displays on the display unit that there is a failure before the preceding stage of the receiving circuit of the slave station C, and prompts the operator to confirm. Also, after detecting loop break,
When data is not sent from the slave station of the master station, it can be considered that a failure has occurred in a portion before the preceding stage of the receiving circuit of the master station. Note that the value of the timer B ₁ .about.B ₄ in each slave station A~D, as described in FIG. 2, B ₁ <
They are set so that B ₂ <B ₃ <B ₄ .

As described above, according to the first embodiment, the master station and the slave station are provided with data transmission / reception processing after detecting a loop break, and it is possible to clearly determine which part of the loop interface is normal and which part is not normal. Therefore, it is expected that the efficiency of the operation of searching for the cause of the failure by the operator is improved. Also, no special hardware is required for this function. For example, the timers A and B determine whether or not a time-out has occurred by comparing a timer setting value preset in a memory in a control unit of a master station or a slave station with a count value of a unit time signal such as a clock. Can be.

Embodiment 2 FIG. 4 is a diagram showing a communication control circuit of a master station and slave stations according to Embodiment 2 of the present invention. The configuration of the communication system according to the second embodiment is the same as that of FIG. 8, but the hardware configurations of the master station and the slave stations are different only in the communication control circuit in FIG. In FIG. 4, each communication control circuit 20 of the master station and the slave station according to the second embodiment includes a control circuit 2
1, receive element 22, drive element 23, relay 24
And 25. 26 is a relay control signal, S is a transmitting end, and R is a receiving end. The master station and the slave station have the same configuration.

Each communication control circuit 20 receives input serial data at a receiving element 22 via a relay 24, performs data processing at a control circuit 21, and outputs output serial data from a drive element 23 via a relay 25. The switching contacts of the relays 24 and 25 are controlled by the relay control signal 26 output from the control circuit 21 so that the communication direction of the loop interface is opposite to the next forward direction.

Forward communication Each switching contact of the relays 24 and 25 of the master station and each slave station is shown in FIG.
The state shown in (1) indicates the connection of the forward communication, and the forward communication order of the loop interface is as follows. Forward communication order: master station-slave station A-slave station B-slave station C-slave station D-master station A forward connection state for forming a forward communication path is as follows. Forward connection state: S of master station-R of slave station A-S of slave station A-
R of slave B-S of slave B-R of slave C-S of slave C-R of slave D-R of slave S-R of master.

Reverse communication The case where the switching contacts of the relays 24 and 25 of the master station and the slave stations are switched to the opposite side from the state shown in FIG. The direction communication order is as follows. Reverse communication order: master station-slave station D-slave station C-slave station B-slave station A-master station The reverse connection state for forming a reverse communication path is as follows. Reverse connection state: R of master station-S of slave station A-R of slave station A-
S of slave B-R of slave B-S of slave C-R of slave C-S of slave D-R of slave D-S of master.

FIG. 5 is a flowchart showing a communication control process of the master station according to the second embodiment of the present invention. The numeral following S in the figure indicates a step number. The flowchart of FIG. 5 will be described. In S41 of FIG. 5, both the timer A and the timer C are started. In S42, the master station sends a token to the slave station A. Here, the value of the timer C is set to be longer than the sum of the value of the timer A and the maximum value of the timer B. The purpose of the timer C is to switch the communication direction between the forward direction and the forward direction by the timeout of the timer C, and to change the value of the timer B of each slave station according to the switching. The value of the timer A is set in the same manner as in FIG. In step S43, it is monitored that the token transmitted in step S42 returns around the loop interface, and it is determined whether or not the token has been received. If a token has been received, the process proceeds to S44; otherwise, the process proceeds to S45.

In S44 of FIG. 5, it is determined whether or not data from the slave station is added to the token. If data is added, the data added is analyzed in S54. If the data from the slave station has not been added, the process returns to S41 to output the next token. S
If the token has not been received at 43, it is determined at S45 whether or not the timer A has timed out. If not, the process returns to S43 to monitor the reception of the token. If the result of the determination in S45 is a timeout, the process proceeds to S46, and the timer B is started.
The value of the timer B is set in the same manner as in FIG.

In S47, it is determined whether or not data has been received from the slave station. If data has been received, in S49,
The received data is analyzed to recognize the slave station that sent the data. Then, the process proceeds to S50. If the result of determination in S47 is that data has not been received from the slave station,
Then, it is determined whether or not the timer B has timed out. If not, the process returns to S47 to confirm whether or not data has been received from the slave station. If the result of the determination in S48 has timed out, the flow proceeds to S50. S5
In the case of 0, it is determined whether or not the timer C has timed out, and if it has timed out, the process proceeds immediately to S51, and if not, the process waits until the time out. When the timer C times out, the process proceeds to S51.

In S51, the switching contacts of the relays 24 and 25 in FIG. 4 are switched from the forward connection state to the reverse connection state (the switching contact in FIG. 4 is on the opposite side). Then, the process proceeds to S52. In S52, it is determined whether or not the check by the two-way communication path in the loop communication path before switching the switching contacts of the relays 24 and 25 in S51 and the backward communication path after switching is completed. Then, if the check has only been performed on the communication path in one direction, the process returns to S41 (see A in FIG. 5), and the processing in S41 to S51 is performed again on the communication path in the other direction.

If it is determined in S52 that the check by the two-way communication path has been completed, the process moves to S53, and based on the slave number from which the data acquired in S49 has been transmitted, the slave having a normal connection state and the slave having an abnormal connection state are determined. The result of the communication in both directions is displayed together on the display unit to prompt the operator to confirm.

FIG. 6 is a flowchart showing the communication control processing of the slave station according to the second embodiment of the present invention. The numeral following S in FIG. 6 indicates a step number. FIG. 6 shows a communication control process of the slave stations A, B, C, and D of the communication system. The flowchart of FIG. 6 will be described below. In S61 of FIG. 6, both the timer A and the timer C are started, and in S62, it is determined whether or not a token has been received. Here, the values of the timers A and C are set as in the case of FIG. When the token is received, the frame received is analyzed in S63, and it is determined whether or not the frame is addressed to the own device. If the frame is addressed to the own device, the process proceeds to S64, and after copying the received frame to the memory in the device, the process proceeds to S65,
The received frame is transmitted as it is to the next slave station in the loop (the slave station D is the master station). If it is determined in S63 that the frame is not addressed to the own device, the process proceeds to S65, and returns to S61 to wait for the next token.

If it is determined in step S62 that the token has not been received, the process proceeds to step S66, and it is determined whether or not the timer A has timed out. If not, the process returns to step S62 to confirm whether or not the token has been received. S6
If the result of the determination in 6 is a timeout, the process proceeds to S67 and the timer B is started. Here, timer B of each slave station
Is initially set in the same manner as in FIG. 2, but when the communication direction of data communication is subsequently switched from the forward direction to the reverse direction, the value of the timer B needs to be changed in accordance with this switching. That is, the timer values B ₁ ′, B ₂ ′, B ₃ ′, B ₄ ′ at the slave stations A, B, C, D in the forward direction are represented by B
₁ ′ <B ₂ ′ <B ₃ ′ <B ₄ ′, and the timer values B ₁ ″, B ₂ ″, B ₃ ″, B at the slave stations A, B, C, D in the reverse direction. ₄ "B _1">
B ₂ "> B _3"> each B ₄ so as to "set.

After S67, the process proceeds to S68, in which it is determined whether or not data has been received from a slave station at the preceding stage of the loop. If data has been received, the process proceeds to S71. If data has not been received, the process proceeds to S71. Goes to S69. In S71, the slave station number of the own apparatus is added to the received data, and the data is transmitted to the slave station next to the loop, and then the process proceeds to S72.

If it is determined in S68 that data has not been received from the slave station at the preceding stage of the loop, then in S69,
It is determined whether or not the timer B has timed out. If the time has not timed out, the process returns to S68 to confirm whether data has been received from the slave station at the preceding stage of the loop. If it is determined in S69 that the time-out has occurred, the flow advances to S70 to send the slave station number of the own apparatus to the slave station next to the loop. Then, the process proceeds to S72. In S72, it is determined whether or not the timer C has timed out,
If the time-out has occurred, the process proceeds directly to S73, and if not, the process waits until the time-out occurs. When the timer C times out, the process proceeds to S73.

In S73, the switching contacts of the relays 24 and 25 in FIG. 4 are switched from the forward connection state to the reverse connection state (the switching contact in FIG. 4 is on the opposite side). Then, the process proceeds to S74. In S74, it is determined whether or not the check has been made in the forward communication path of the loop interface before switching the switching contacts of the relays 24 and 25 in S73 and in the two-way communication path in the backward communication path after switching. If the check using only the one-way communication channel has been completed, the process proceeds to S75. If the check using the two-way communication channel has been completed, the process proceeds to S76.

In S75, the value of the timer B is changed from B 'to the value of B "previously stored in the program, and the flow returns to S61 to confirm the communication in the reverse direction (see FIG. 6A). ), And repeat the processing of S61 to S73.If it is determined in S74 that the communication confirmation in both directions has been completed,
Proceeding to S76, the value of the timer B is returned from B "to the value of B 'previously stored in the program, and the operation of the communication control processing of the slave station ends.

Here, the reason why the value of the timer B is changed in S75 and S76 will be described. Timer B sets the timing at which the slave station sends its own device number to the next station after detecting the loop break by timer A. Therefore, it is necessary to shift the time in each slave station so that each slave station does not output simultaneously, and the timer B of the slave stations A to D in FIG.
The value of ₁ .about.B ₄ has been described as _{B 1 <B 2 <B 3} <B 4. However, in the second embodiment, since there are two communication directions, it is necessary to change the value of the timer B of each slave station so that the time becomes longer sequentially according to the communication directions. That is, when the communication direction is forward communication (master station → slave station A → slave station B → slave station C → slave station D → master station), each slave station A, B, C,
The value of the timer B of D is B ₁ ′ <B ₂ ′ <B ₃ ′ <
B ₄ ′. In the case of reverse communication (master station → slave station D → slave station C → slave station B → slave station A → master station), B ₁ ″> B ₂ ″>
This is because it is necessary to satisfy B ₃ ″> B ₄ ″.

FIG. 7 is a sequence diagram showing a communication operation example of the master station and the slave station when the loop is broken according to the second embodiment of the present invention. The master station and the slave station perform the communication control processing of FIGS. 5 and 6, respectively. As a result, when an interface disconnection accident occurs between the slave station A and the slave station B and between the slave station B and the slave station C, the operation is performed as shown in FIG. Hereinafter, the operation of FIG. 7 will be described. When the power is turned on to the system, first, an operation by forward communication is performed. That is, the master station sends a token (indicated by P in the figure) to the slave station A. When the slave station A receives the token, it sends a frame (P, CNA) to the slave station B in which data (indicated by CNA in the figure) indicating that the own device is operable is added to the token (P). However, since the line between the slave station A and the slave station B is broken, the slave station B does not receive this frame.

Therefore, the slave station B starts the timer B ₂ ′ after the timer A times out, and
_{When 2} 'times out, it sends its slave station number to slave station C. However, the slave station B does not receive data from the slave station B because the slave station B and the slave station C are disconnected. Therefore, the slave station C starts the timer B ₃ ′ after the timer A times out. When the timer B ₃ ′ times out, the slave station C sends the slave station number (indicated by C in the figure) of the slave station to the slave station D. The slave station D receives the slave station number (C) of the slave station C, adds the slave station number (D) of its own apparatus to the frame (shown in FIGS. C and D), and sends the frame to the master station. The master station receives it.

When the time further elapses and each device detects the timeout of the timer C, the relays 24 and 25 of the communication control circuit are switched. That is, the communication direction is switched from forward communication to backward communication. The master station outputs a token to the slave station D by reverse communication, and the slave station D adds data indicating that the own device is in an operable state to the slave station (indicated by P and CND in the figure). Send the frame to The slave station C adds to the received frame data indicating that the apparatus itself is operable (P, C in the figure).
A frame is transmitted to the slave station B (indicated by ND and CNC). However, since the disconnection has occurred between the slave station C and the slave station B, the frame does not reach the slave station B.

Therefore, the slave station B starts the timer B ₂ ″ after the timer A times out. When the timer B ₂ ″ times out, the slave station B sends its slave station number (indicated by B in the figure) to the slave station A. However, slave station B
And the slave station A are also disconnected, so the slave station A does not receive anything. Therefore, the slave station A also starts the timer B ₁ ″ after the timer A times out, and when the timer B ₁ ″ times out, sends the slave station number (indicated by A in the figure) of its own device to the master station. The master station receives only the slave station number (A) of the slave station A. In the example of FIG. 7, since the slave station numbers of the slave station C and the slave station D are transmitted at the time of the first forward communication, it can be considered that the preceding stage of the receiving circuit of the slave station C is out of order. . At the time of the next reverse communication, since the slave station number of the slave station A has been sent, it can be considered that the preceding stage of the receiving circuit of the slave station A is out of order. Based on the two communication direction information, the master station can display on the display section that a failure has occurred in the stage before the receiving circuit of the slave station C and before the stage of the receiving circuit in the slave station A, and can prompt the operator to confirm. .

As described above, according to the second embodiment, the master station and the slave station are provided with the data transmission / reception processing after detecting the loop break, and the communication control circuits of the master station and the slave station are provided with relays to provide the communication direction of the loop interface. Is controlled to perform data transmission / reception processing in both the forward and reverse directions, so that a maximum of two failures can be detected by one search. In addition, if only one location has a failure by searching in both directions, the location can be specified, and it is possible to clearly determine which part of the loop interface is normal and which location is the failure. Can be expected to be more efficient.

The timers A, B, and C of the master station and the slave stations in the first and second embodiments correspond to the first, second, and third timers described in the claims, respectively.

[0044]

As described above, according to the present invention, the master station and a plurality of slave stations are connected in a loop, and the master station and the slave stations are connected to each other based on polling information transmitted from the master station to each slave station at predetermined intervals. And a method of determining a loop break point of a loop interface in a system for performing data communication between slave stations, wherein a first timer and a second timer are provided for the master station and each slave station, and the first timer Is set longer than the transmission cycle of the polling information,
The polling information is started at the same time as the transmission of the polling information, and the timeout causes the master station and the slave station to detect a loop break, respectively. The second timer is started after the loop break is detected, and the timer value in each slave station is communicated by data communication. Each slave station is set so as to take a long time sequentially according to the communication direction of the slave station. When the slave station receives the slave station number from the slave station in the communication direction before the timeout of the second timer, the slave station automatically includes the slave station information in the received information. The information to which the slave station number of the device is added is transmitted to the next slave station in the communication direction, and the slave station number of the own apparatus is transmitted to the next slave station in the communication direction due to the time-out. Since the loop break point is determined based on the information including the single or plural slave numbers which can be received from the slave station, the loop interface is determined. If the loop disconnection occurs in the scan, which part of the loop interface is normal, since what parts are not normal can be determined clearly, improving the efficiency of search work fault cause by the operator.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating communication control processing of a master station according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart illustrating a communication control process of a slave station according to the first embodiment of the present invention.

FIG. 3 is a sequence diagram illustrating a communication operation example of a master station and a slave station at the time of loop disconnection according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a communication control circuit of a master station and a slave station according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing communication control processing of a master station according to Embodiment 2 of the present invention.

FIG. 6 is a flowchart illustrating communication control processing of a slave station according to the second embodiment of the present invention.

FIG. 7 is a sequence diagram illustrating a communication operation example of a master station and a slave station when a loop is broken according to the second embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration example of a communication system in which a plurality of stations are connected in a loop.

FIG. 9 is a block diagram illustrating a hardware configuration of a master station and a slave station in FIG. 8;

FIG. 10 is a time chart showing a communication sequence when the power of the system in FIG. 8 is turned on.

11 is a time chart showing an example of a data communication sequence from a master station to a slave station in the system of FIG. 8;

FIG. 12 is a flowchart showing communication control processing of a main station of the system of FIG. 8;

FIG. 13 is a flowchart showing communication control processing of a slave station in the system of FIG. 8;

14 is a diagram illustrating an example of a failure in a loop interface of the system in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CRT 2 Control part 3 Keyboard 4 Connection cable 5 Connection cable 11 CPU 12 CPU peripheral circuit 13 Memory 14 Display part control circuit 15 Display part 16 Input part control circuit 17 Input part 18, 20 Communication control circuit 19 CPU bus 21 Control circuit 22 Receive element 23 Drive element

Claims (2)

[Claims] A system in which a master station and a plurality of slave stations are connected in a loop, and perform data communication between the master station and slave stations and between slave stations based on polling information transmitted from the master station to each slave station at predetermined intervals. In the method for determining a loop break point of a loop interface in the above, a first timer and a second timer are provided for each of the master station and each slave station, and the first timer has a value longer than a transmission cycle of the polling information. It is set to a time and started at the same time as the transmission of the polling information, the master station and the slave station respectively detect a loop break by the timeout, and the second timer is started after detecting the loop break, and The timer values in the slave stations are set so as to be sequentially longer according to the communication direction of data communication, and each slave station sets the second timer If the slave station number is received from the previous slave station in the communication direction before the timeout of, the information obtained by adding the slave station number of the own apparatus to the received information is transmitted to the next slave station in the communication direction. The slave station number is transmitted to the next slave station in the communication direction, and the master station determines a loop break point based on information including the one or more slave station numbers that can be received from the last slave station in the communication direction. Loop break point determination method of the loop interface to be performed. 2. A loop connection switching means for switching the communication direction for performing data communication by connecting the master station and a plurality of slave stations in a loop to a forward direction and a reverse direction is additionally provided for the master station and each slave station. Further, a timer value changing means for changing the value of the second timer in each of the slave stations so as to sequentially take a long time in accordance with the communication direction according to the switching of the loop connection switching means is additionally provided for each of the slave stations. Further, a third timer is additionally provided for the master station and each slave station, and the third timer calculates a value of the third timer by a sum of a value of the first timer and a maximum value of the second timer value. Is also set to a long time, is started at the same time as the transmission of the polling information, the connection is switched by the loop connection switching means and the timer value is changed by the timer value changing means due to the timeout, The station determines a loop break point in forward and reverse communication directions based on information including the single or plural slave numbers in both directions that can be received from the last slave in each communication direction. 2. The method for judging loop breakage of the loop interface according to 1.