JPH0351143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to a loop type network system that allows information to be transmitted without any trouble even when a transmission line is disconnected.

<<Background of the Invention>> An example of a conventional loop type network system is the one disclosed in Japanese Patent Application Laid-Open No. 129048/1983. As shown in Figure 1, for example, three stations A, B, and C are each connected in a loop with a single transmission path, and information is transmitted in one direction of the loop (indicated by an arrow in the figure). It is transmitted only in the counterclockwise direction (as shown).

By the way, in a network system connected in a loop through a single transmission line as described above, if a break in the transmission line occurs, information may be transmitted only in one direction of the loop. Normally, information is no longer transmitted beyond the point of disconnection, causing the entire system to go down.
A loopback method is used to prevent downtime.

This means that, for example, if the transmission line _L3 for transmitting information from station C to station A is disconnected, station A will detect the disconnection of this transmission line _L3 and detect the disconnection of this transmission line _L3 . In addition to informing stations B and C, the necessary information can be transmitted to each station by performing bidirectional communication at predetermined timings such as A→B→C→B→A→B→... This is how it was done.

As shown in Fig. 2, each station (station B is shown as a representative in Fig. 2) is configured to perform loopback processing in the event of a break in the transmission line, as described above. It is equipped with a switch circuit 1 for switching, and when the transmission line is normal, the input line In is connected to the transmission line _L1 from the previous station A so that information is transmitted in one direction of the loop as shown in the figure. connected,
The output line OUT is connected to the transmission line _L2 to the next stage station C.

When a disconnection occurs, the switch circuit 1 is switched at a predetermined timing to switch the transmission/reception direction.

In the figure, CPU2 is a microcomputer that controls communication, SCI (serial
Communication interface) 3 is an interface for inputting and outputting transmission and reception signals,
It has parallel/serial conversion and serial/parallel conversion functions.

ROM 4 and RAM 5 are memories, and interface 6 is an input/output port. An example of a one-chip microcomputer with such a configuration is HD-6801 manufactured by Hitachi.

The structure of the information transmitted in the above network system is, for example, as shown in FIG.
Two channel slots SLT for control data
1, SLT2, and a disconnection information slot SLT3 that notifies the disconnection of the transmission line.
The slot SLT3 for sending the disconnection information is 8.
It has a bit structure.

For example, if a disconnection occurs in the transmission line _L3 between station C and station A,
Since station A does not receive information from station C for a predetermined period of time, the transmission line
It is detected that a disconnection has occurred in _L3 , and from then on, the most significant bit (MSB) of the disconnection information slot SLT3 is
Data with D ₇ as “1”, that is, [10000000]
Data like this, if expressed in binary coded hexadecimal, is
The data of [80H] (H indicates a hexadecimal number) is transmitted to the next stage station B.

At station B, during a period when the transmission line is normal, the content of the disconnection information slot SLT3 is [OOH], but since its MSB is "1", it means that there is a disconnection in the transmission line. , and sends similar disconnection information to station C, and repeats switching of the transmission direction at a predetermined period T ₁ after a predetermined time T _B has elapsed.

Similarly, station C determines that a wire breakage has occurred based on the wire breakage information from station B, and thereafter moves to an operation of repeatedly switching the communication direction at a predetermined period _T1 after a predetermined time T _C has elapsed.

The above operation is schematically shown in FIG. In the same figure, before the wire breakage occurs (before the wire breakage detection time t ₀ )
In , each station A, B, and C had a constant counterclockwise transmission direction (indicated by L in the figure), but after the time t ₀ when station A detected a disconnection, each station The station has a constant period T ₁
The transmission direction is repeatedly switched between counterclockwise (L) and clockwise (R) to perform bidirectional communication.

In this way, after a break in the transmission line is detected, each station repeatedly switches the transmission line at a constant cycle _T1 , thereby transmitting information to all stations. .

However, as mentioned above, during two-way communication,
If the communication direction switching cycle is set to the same cycle _T1 for all stations, it is impossible to determine whether the information has been received by the destination station. It is necessary to increase the number of data transmissions or to make the switching period of the transmission direction relatively long, which results in a slow transmission speed.

In addition, since the communication direction switching cycle is based on a timer built into each station, variations in the precision of these timers may cause
There is a risk that a difference may occur in the communication direction switching timing for each station, and even if the difference is small at first, it becomes large after a long time, and the communication direction with the adjacent station may become completely opposite. (For example, when the own station is rotating counterclockwise, the adjacent station is rotating clockwise.) In such a case, it becomes impossible to transmit information.

《Object of the invention》 This invention was made in view of the above circumstances, and its purpose is to improve the reliability of communication when performing loopback type two-way communication after a disconnection occurs in the transmission line. It is an object of the present invention to provide a loop type network system that can improve performance and prevent information transmission from becoming impossible due to a shift in transmission direction switching timing.

<<Structure of the Invention>> Hereinafter, the structure of the present invention will be briefly explained using the claim correspondence diagram of FIG.

As shown in the figure, the loop type network system of the present invention has a plurality of stations (A, B,
C and D) are connected in a loop through one transmission path, and information is transmitted only in one direction of the loop during a period when the transmission path is normal.

Then, if each station does not receive a signal from the previous station in a predetermined communication direction for a certain period of time or more, it adds a position signal indicating the position of the station from the disconnection point to the communication data and transmits it, and then changes the direction of transmission and reception. a first means 101 for inverting the position signal; when the communication data to which the position signal is added is input, the position signal is converted into a position signal indicating the position from the disconnection point of the station based on the input position number; a second means 102 for determining whether the station is an end station by determining whether the station position indicated by the changed position signal is a predetermined station position; If the means 102 determines that the station is not at the predetermined station position, the third means 103 adds the changed position signal to the communication data and transmits it, and then reverses the transmission/reception direction.
If the second means 102 determines that the station is at the predetermined station position, the transmitting/receiving direction is reversed, the changed position signal is added to the communication data and transmitted, and the transmitting/receiving direction is changed again. and fourth means 104 for inverting.

When the disconnection is detected, a communication direction reversal operation is started from the station where the disconnection has been detected, and the communication direction reversal operation is sequentially transferred to the next stage station, and the station where the disconnection has been detected and the disconnection are The station is configured to repeatedly move the communication direction reversal operation back and forth between the station where the disconnection has been detected and the adjacent station as the turning point.

With this, for example, if the transmission line that transmits information from station D to station A is disconnected, the disconnection will be detected at station A, and the communication direction will be reversed from station A → B → C → The procedure is as follows: D→C→B→A→B→
The movement of the communication direction reversal operation will be repeated back and forth at all stations with the return point at .

<<Description of Embodiments>> Embodiments of the present invention will be described in detail below with reference to FIG. 6 and the subsequent drawings.

The configuration of the loop type network system of this embodiment is similar to the conventional network system shown in FIG.
It is formed by coupling C into a single transmission line loop. Furthermore, since the configuration of each station is the same as that shown in FIG. 2, FIGS. 1 and 2 are used instead for their configuration diagrams.

FIG. 6 is a flowchart showing the contents of the processing executed in the stations making up the loop type network system of this embodiment. The process shown in the figure is executed by the CPU 2 in FIG.

Below, based on the flowchart shown in the same figure,
Communication control processing of the loop type network system of this embodiment will be explained.

The format of the information transmitted between each station is the same as in the conventional example, as shown in Figure 3.
The frame has a marker slot for frame identification.
Consists of SYN and three data slots SLT1 to SLT3. Among the data slots, SLT
1 and SLT2 are channel slots,
Terminal equipment connected to each station (e.g.
Contains control signal data for headlamps, mirrors, turn signal lamps, etc.).

The SLT3 includes 8-bit disconnection information as a position signal indicating the position of the station from the disconnection point. If there is no abnormality in the transmission path, this is expressed as [00H] in binary coded hexadecimal data (this is expressed in binary code as [00H]).
[000000000]).

During the period when the transmission path is normal, each station follows steps (1)→(2)→(3)→(4)→
(5)→(17)→(18)→(19) or (1)→(12)→
The processing of (13) → (14) → (17) → (18) → (19) is performed, and information is sent only in one direction (counterclockwise, as shown in Figure 1, similar to the conventional example) in a loop. will be communicated.

In the process of step (1), it is determined whether or not a received signal is input to the SCI 3 based on the state of the SCI 3.

In the process of step (2), the received signal input to the SCI 3 is read into the CPU 2.

In the process of step (3), a process of clearing a soft timer _TM1 for detecting transmission line disconnection, which will be described later, is performed.

In step (4), a flag FLG1 is set to store whether or not loopback type two-way communication is being performed.
It is determined whether or not is ON. In this case, since the transmission path is normal, FLG1 is OFF, the determination result is NO, and the process proceeds to step (5).

In step (5), the data in the disconnection information slot SLT3 in the received data is read and this data is
Determine whether “1” is written in the MSB of SLT3. If this MSB is “0”, it is determined that the transmission line is normal, and if it is “1”, it is determined that a disconnection has occurred. judge.

In step (17), processing is performed to set the data of the slot to be transmitted. this is,
This is because the configuration is such that data is transmitted for each slot each time the process shown in FIG. 6 is completed.

In step (18), the data for one slot set in step (17) is output from the SCI 3 to the transmission line.

In step (19), the above flag FLG1 is set again.
Determine whether it is ON or not, in this case
Since FLG1 is OFF, the determination result is NO.

In step (12), the same processing as in step (4) is performed.

In step (13), processing is performed to advance the soft timer _TM1 for wire breakage detection, and in the next step (14), it is determined whether the contents of the timer _TM1 have exceeded a preset timer time _T0 . A determination is made.

Next, processing when a disconnection occurs in the transmission line will be explained below in order for each station.

For example, if a disconnection occurs in the transmission line _L3 that transmits information from station C to station A, first, station A will not receive the information from the preceding station C, so step (1) in FIG. ) is NO, and the process of step (12) is then performed.

In step (12), a flag indicating whether or not bidirectional communication using the loopback method is being executed is set.
It is determined whether FLG1 is ON or not, and at station A, the flag is
Since FLG1 is still OFF, the determination result is
The result is NO, and the next steps (13) and (14) are performed.

In step (14), since a disconnection has occurred in the transmission line _L3 , the timer time _T0
Since no information is transmitted from station C to station A even if timer TM ₁
When the timer reaches the timer time _T0 , it is determined that a disconnection has occurred in the transmission line _L3 between the previous station C and the next station A, and the next step (15) is executed.

In step (15), distance data is stored in a distance memory Pset that stores the number of the next station from the point where the disconnection occurred. That is, as described above, since there is a disconnection between station C and station A, station A is the station at the disconnection location, and therefore "0" is stored in the distance memory Pset. Therefore, "1" is stored in the next station B, and "2" is stored in the station C. Details of these processes will be described later.

In the next step (16), the disconnection information slot
Write the information [80H] (H represents hexadecimal) to SLT3 in binary coded hexadecimal. That is, a process of writing "1" to the MSB (highest bit D ₇ ) of SLT3 consisting of 8-bit data is performed.

Thereafter, the process of step (10) is executed, the flag FLG1 is set to ON, and it is stored that the two-way communication operation will be started from now on.

Then, the process proceeds to step (11), where a process is performed in which 1 is added to the contents of the flag FLG2 for controlling communication direction switching.

As described above, in station A, upon detecting a wire breakage, processing is performed to set the contents of the distance memory Pset and the wire breakage information slot SLT3, and to set predetermined data in the flag FLG1 and the flag FLG2.

Then, through the processing in steps (17) and (18), the disconnection information slot SLT3 (content: [8OH]) set in step (16) is sent to station B.

In the next step (19), the above steps
Since the flag FLG1 is turned ON in step (10), the determination result becomes YES, and the process of step (20) is then executed.

In step (20), the disconnection information slot
A determination is made as to whether or not the output of SLT3 has ended. While the disconnection information slot SLT3 is outputting, the determination result becomes NO, and when the output of the SLT3 is finished, the next step (21) is executed.

In step (21), it is determined whether the flag FLG3, which stores whether or not the output from the disconnection information slot SLT3 has ended, is ON after switching the communication direction. In this case, since FLG3 is still OFF, the determination result is NO, and the process of the next step (24) is executed.

In step (24), the result of adding the contents of the distance memory Pset set in step (15) above and the contents of the received disconnection information slot _SLT3R is [83H].
A determination is made as to whether or not it is. At this time, since information from station C is not received at station A, the above-mentioned SLT3 _R is undefined, and the determination result is OF _H (value when there is no predetermined signal).

Therefore, the process in step (25) is executed next, and the flag FLG2 set in step (11) above is
A determination process is performed to determine whether or not is ON (that is, whether a value of 1 or more is set), and in this case, the content of flag FLG2 is “1” in step (11). Therefore, the discrimination result is
YES, and the process of the next embodiment (26) is executed.

In the process of step (26), the above flag FLG
A process of subtracting 1 from the contents of 2 is performed, and as a result, the contents of the flag FLG2 at station A become "0" again.

Thereafter, the process of step (23) is executed, and a switching signal is output from the interface 6 to the switch circuit 1 for switching the transmission/reception direction shown in FIG. 2, thereby switching the communication direction (in this case, (reversal from counterclockwise to clockwise) is performed.

Looking at the above operation in the operation timing chart of FIG. 8, station A detects that a break in the transmission line between station C and station A has occurred at time ta ₁ , and detects the predetermined break. After transmitting the information to station B, change the communication direction from counterclockwise (L) to clockwise (R) (A ₁ in the diagram)
Ru.

From then on, at station A, step (1)
→(12)→(17)→(18)→(19)→(20)→(21)
→(24)→(25)→(1)→... The process is repeatedly executed.

Next, as shown in FIG. 8, station B receives disconnection information slot SLT3 from station A at time _tb1 .
The following processing is executed.

Upon receiving the information from station A, steps (1) -> (2) -> (3) -> (4) -> (5) are performed, and in step (5), the received disconnection information is processed. It is determined whether the MSB of slot SLT3 is "1" or not, and since SLT3 has been rewritten to [8OH] at the station A, the determination result is YES, and the next step is started.
Processing (6) is executed.

In step (6), the contents of disconnection information slot SLT3 sent from station B are as follows:
Disconnection information slot received from station A
Processing is performed to add "1" to SLT3 _R (content is [80H]). As a result, the content of SLT3 becomes [81H].

Next, in step (7), predetermined data is set in the distance memory Pset at station B. In other words, the received disconnection information slot SLT
3 After adding 1 to the contents of _R , set the MSB to “0”
Set the value set in Pset. At this time, at station B, the received disconnection information slot
Since the content of SLT3 _R is [80H], adding 1 will result in [81H], and setting the MSB to "0" will result in [01H] (hereinafter referred to as "1").

Next, in step (8), the distance memory Pset is
It is determined whether the content of is "2" or not. At this time, since Pset was set to "1" in step (7), the determination result is NO, and the next steps (10) and (11) are executed.

As described above, upon receiving SLT3 of [80H] from station A, station B sends the disconnection information slot SLT3.
Set the content to [81H] and set "1" to the distance memory Pset.
A process is performed to set the .

Then, the data is transmitted through the processing of steps (17) and (18), and the processing of the next step (19) becomes YES, so the steps (20) → (21)
→The processing in (24) is performed.

In step (24) above, the distance memory
The content of Pset is "1" and the content of the received disconnection information slot _SLT3R is "80H", so the addition result of these is [81H] and the determination result is
The result is NO, and the following steps (25) → (26) →
(23) After the process of →... is executed and flag FLG2 is reset to "0", the communication direction at station B is changed from counterclockwise (L) to clockwise (R).
An operation to switch to is performed.

Looking at the above operation in Figure 8, the above process is executed from time tb ₁ when station B receives SLT3 of [80H] from station A, and SLT3 of [81H] is sent to station C. Later, the communication direction will be switched from counterclockwise (L) to clockwise (R) (B ₁ in the figure). After that, step (1)
→(12)→(17)→(18)→(19)→(20)→(21)
→(24)→(25)→(1)→... The processing is repeated.

As described above, when station B switches the communication direction, information is communicated from station B to station A. At station A, the processing at this time is as follows: (2)→(3)→(4)→(17)→(18)→(19)→
(20) → (21) → (24) → (25) → (1) →..., and the communication direction is not switched. In addition, in the process of step (24) at this time, the content of Pset in station A is "0", and the disconnection information slot SLT received from station B is
Since the content of 3 _R is [81H], the result of these additions is [81H], and the determination result is NO.
Further, the flag FLG2 is OFF, and the determination result in step (25) is NO.

Next, at station C, the disconnection information slot whose content is [81H] is sent from station B.
The following processing is executed by receiving SLT3.

First, by receiving SLT3 of [81H] from station B, steps (1)→(2)→(3)→(4)
→(5)→(6) are performed, and in step (6), the process of adding 1 to the content [81H] of the received _SLT3R as the content of the disconnection information slot SLT3 sent from station C. As a result, [82H] is rewritten as the contents of SLT3.

Next, in step (7), the arithmetic processing described for station B is executed in the distance memory Pset in station C, and as a result, data "2" is stored in Pset.

Therefore, the determination result in the next step (8) is YES, the process in step (9) is executed, and the flag is set.
Set the contents of FLG2 to “1”.

After the flag FLG1 is turned ON in step (10), the process in step (11) is performed, whereby the content of the flag FLG2 becomes "2".

Then, step (17) → (18) → (19) →
(20) is executed and the disconnection information slot is
When SLT3 is output, step (21)→
The process in (24) is executed. Note that the SLT3 output in step (18) is sent toward the transmission path where the disconnection occurred, since the station C has not yet switched the communication direction.

In step (24) above, the distance memory
Since the content of Pset is "2" and the content of disconnection information slot SLT3 _R received from station B is [81H], the result of addition of these is [83H], the determination result is YES, and the next The process of step (27) is executed.

The processing in step (27) is performed when the own station
This process determines whether the stations on both sides of the disconnection information (hereinafter referred to as end stations) are located. Specifically, this process determines whether the content of the distance memory Pset is either "0" or "2". Execute processing to determine whether or not. Since the value of Pset at this station C is "2", the determination result is YES and the process of step (28) is subsequently executed.

At step (28), flag FLG2 is set to “1”.
A process is performed to set the . At this time, since the value of the flag FLG2 has already been set to "2" in step (11), the content of the flag FLG2 changes from "2" to "1".

Then, in step (30), a flag FLG3 is set to store whether or not the output of SLT3 has ended.
Set to ON.

Next, when the process starts again from step (1), steps (1) → (12) → (17) → (18) → (19) →
Processing from (20) to (21) is executed, and this time, flag FLG3 is ON, so the process of step (22) is performed next, and flag FLG3 is turned on.
After turning off, the process in step (23) is executed. The process of step (23) is a process of switching the communication direction, and thereby the communication direction of station C is switched from counterclockwise to clockwise.

Looking at this state in Figure 8, the above process is executed from time tc ₁ when station C receives SLT3 [81H] from station B, and once SLT3 [82H] is disconnected. transmission line
L After being output in ₃ directions, the communication direction is clockwise (R)
(C ₁ in the figure).

Next, go to station C again and repeat step (1).
When processing starts from step (1)→(12)→
(17)→(18)→(19)→(20)→(21) are executed, and this time, since flag FLG3 is OFF, the process of step (24) is executed next.

At this time, the communication direction of station C is clockwise (R), and the transmission line _L3 on the receiving side is disconnected, so no information is received. Therefore, the determination result in step (24) is NO, and the process in step (25) is subsequently executed.

In step (25), since the flag FLG2 was set to "1" in step (28), the determination result is YES and the process in step (26) is executed. In this step (26), "1" is subtracted from the content of flag FLG2, and as a result, the content of LFG2 becomes "0".

Thereafter, the process of step (23) is executed and the communication direction is switched again. As a result, the communication direction of station C is clockwise (R).
The rotation is then switched to counterclockwise (L) again. Looking at this in Figure 8, after switching the communication direction clockwise at time C ₁ and sending SLT3 of [82H] to station B at time tc ₂ ,
At _C2 , the process of switching the communication direction to the counterclockwise direction is performed again.

Next, suppose that station B, whose communication direction has been switched clockwise, receives SLT3 of [82H] from station C at time tb ₂ in FIG. 8. Steps (1)→(2)→ (3)→(4)→(17)→
The processing is executed as (18) → (19) → (20) → (21) → (24), and in the process of step (24),
Since the content of the distance memory Pset at station B is "1" and the content of the disconnection information slot _SLT3R received from station C is [82H], the result of these additions is [83H]. The determination result becomes YES, and the process of step (27) is then executed.

At step (27), since the content of the distance memory Pset at station B is "1", the determination result is NO, and the process at step (29) is then executed.

In step (29), the contents of the disconnection information slot SLT3 sent from station B to station A and the value of distance memory Pset are changed.

The contents of disconnection information slot SLT3 sent from station B above can be changed by station C.
A process is performed in which 1 is added to the contents of the disconnection information slot SLT3R received from the _SLT3R , and this result is used as the data of SLT3. Now, since SLT3 of [82H] is being received from station C, the contents of SLT3 of station B are [82H] + 1 =
It becomes [83H].

In addition, the value of Pset is the new value with the MSB of SLT3 changed by the above processing as “0”.
Processing is performed to set the value of Pset, in this case SLT
Since 3 has been changed to [83H], the contents of Pset will be changed to "3".

After the above process is executed, the flag FLG3 is set to ON by the process of step (30).

Then, when processing starts again from step (1), steps (1) → (12) → (17) → (18)
→(19)→(20) are executed, and [83H] is sent from station B to station A.
SLT3 is sent.

When the output of SLT3 is finished, the process moves from step (20) to step (21), and since flag FLG3 is ON, flag FLG3 is turned OFF in step (22). By the process of the post-step (23), the communication direction of station B is switched from clockwise to counterclockwise.

Looking at this in Figure 8, the above process is executed from time tb ₂ when SLT3 of [82H] is received from station C, and SLT3 of [83H] is sent from station B to station A. After being transmitted (B ₂ in the figure), the communication direction is switched from clockwise to counterclockwise.

Then, station B will not switch the communication direction until information is received again.

Also, in this state, station C will receive the state of affairs from station B, but station C will receive the determination result in step (24) as NO.
And since the flag FLG2 is OFF, the communication direction is not switched.

Next, when station A, where the communication direction is switched clockwise, receives SLT3 of [83H] from station B (see Figure 8).
ta ₂ ), the following processing is executed at station A.

By receiving the information from station B, steps (1)→(2)→(3)→(4)→(17)→(18)
→ (19) → (20) → (21) → (24) are executed, and in the process of step (24), the content of the distance memory Pset at station A is “0” and the station Since the content of the disconnection information slot _SLT3R received from B is [83H], the determination result is YES and the process of step (27) is executed next.

In the process of step (27), since the content of Pset at station A is "0", the determination result is YES and the process of step (28) is executed. As a result, flag FLG2 is set to "1", and then step (30) is started.
flag FLG3 is set to ON.

Then, when the process starts again from step (1), steps (1) → (12) → (17) → (18) → (19) →
Processing is executed as (20) → (21), and this time the flag
Since FLG3 is ON, the flag FLG3 is turned OFF in step (22), and then station A is turned off by the processing in step (23).
The communication direction is switched from clockwise to counterclockwise.

Then, the process of step (1) is started again, and steps (1)→…→(17)→(18)→(19)→(20)
→The process in (21) is executed, and now the flag FLG
Since step 3 is OFF, step (24)
Proceed to. In this process, the contents of Pset are 0 and the communication direction is counterclockwise as described above, so there is no signal from station C, and the contents of SLT3R are OF _H (when there is no signal, the predetermined value OF _H ), so proceed to step (25). Flag FLG in step (30)
Since "1" is set in FLG2, the process proceeds to step (26), the contents of FLG2 are decreased by "1" (that is, it becomes "0"), and the communication direction is changed again by the process of step (23). A switching process is performed. As a result, the direction of communication at station A is switched from counterclockwise to clockwise.

Looking at the above process in Figure 8, after receiving SLT3 of [83H] from station B at time ta ₂ , the communication direction is switched from clockwise to counterclockwise at time A ₂ , and at time ta 3, the communication direction is switched from clockwise to _{counterclockwise} . , After sending SLT3 of [80H] to station B, at the time
At _A3 , the communication direction is switched from counterclockwise to clockwise again.

Next, when station B, whose communication direction has been switched counterclockwise, receives SLT3 of [80H] again from station A (tb ₃ in Figure 8), the following processing is performed. executed.

As the information is received from station A, steps (1)→(2)→(3)→(4)→(17)→(18)
→ (19) → (20) → (21) → (24) are executed, and in the process of step (24), the content of the distance memory Pset at station B at this time is changed to "3". and the content of the disconnection information slot _SLT3R received from station A is [80H], so the determination result is YES and the next step (27) is executed.

In the process of step (27), since the Pset of station B is "3" at this time, the determination result is NO, and the process of step (29) is executed to change the data of SLT3 and Pset again. Processing will be executed.

In other words, the process of adding 1 to the contents of disconnection information slot SLT3 received from station A. At this time, since the contents of SLT3 received from station A is [80H], adding 1 and the value of [81H] becomes the value of station A. SLT to be sent by B
It is set as data 3.

Also, the contents of SLT3 changed as above.
The content of Pset is changed to "1" by processing to set the value of Pset to a value with the MSB set to "0".

Then, in step (30), flag FLG3 is set.
After turning ON, processing starts again from step (1).

In the next process, step (1)→…→(17)→
The processes of (18)→(19)→(20) are executed, and SLT3 of [81H] is transmitted from station B to station C.

After that, the process in step (21) is executed, and since flag FLG3 is ON at this time, the flag is then set in the process in step (22).
After turning off FLG3, the communication direction is switched by the process of step (3). As a result, the direction of communication at station B is switched from counterclockwise to clockwise.

Then, station C receives SLT3 of [81H] from station B again, and station C performs the same process as described above, and receives SLT3 of [81H] from station B. After that, change the communication direction from counterclockwise to clockwise and use SLT3 of [82H].
After sending the data to station B, the process of switching the communication direction from clockwise to counterclockwise is performed again.

Thereafter, the same process as described above is executed at station B and station A, and as shown in FIG. The moving direction of the process is switched, and the process of reversing the communication direction is repeated back and forth between each station.

Furthermore, in station A, when receiving [83H] from station B, processing for switching the communication direction is performed, and processing for sending SLT3 of [80H] to station B is performed every time. When station B received [80H] from station A, it sent [81H] to station C and then switched the communication direction, and when it received [81H] from station C, it sent [83H] to station A. After that, an operation to switch the communication direction is performed. Then, when station C receives [81H] from station B, it executes processing to switch the communication direction, and sends SLT3 of [82H] to station B. In this way, the conditions for switching the communication direction and the data to be sent from the SLT 3 at each station are determined, and a summary of these conditions is shown in FIG.

As can be seen from Fig. 7, after a break in the transmission line occurs, the MSBs of the break information slot SLT3 are all set to "1" and communication is performed, and each station receives the received break information slot _SLT3R. Conditions are set such that the communication direction is switched when the sum of the content and the content of the distance memory Pset of each station becomes [83H].

Therefore, if the number of stations increases further, the same operation can be performed by changing the values serving as the conditions for the reversal operation shown in FIG. That is, for example, if there are 4 stations, the value of Pset will be 0 to 3, the data of SLT3 will be [80H] to [85H], and when the sum of both at each station is [85H], All that is required is a configuration that switches the communication direction.

Note that the general data is constantly output, and when the communication direction matches that of the adjacent station, the general data is exchanged. At this time, position signals are also exchanged along with general data; for example, as shown in Figure 7, with SLT3R and
If the total of Pset does not become [83H], no inversion operation is performed. The dotted line shown in FIG. 8 is a route of communication data (general data) to which an updated position signal (disconnection information) is added.

<<Effects of the Invention>> As explained in detail above, in the loop type network system of the present invention, when a disconnection occurs, the station that detects the disconnection notifies the next station in sequence of the occurrence of the disconnection. When the transmission is completed, the transmission/reception direction at the own station is reversed, and if the transmission line between the own station and the next station is broken, the transmission line from the previous station is When reception is completed, the direction of transmission and reception is reversed, so that necessary information can be reliably transmitted to all stations, and the transmission speed will not become extremely slow.

Furthermore, it is possible to prevent communication with an adjacent station from becoming impossible due to an error in the communication direction switching period for each station.

Furthermore, the program contents of the processing set in each station can be made common to each station, and the number of stations can also be changed freely.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the system configuration of a loop type network system, Figure 2 is a block diagram showing the hardware configuration of each station, Figure 3 is a diagram showing the format of communication data, and Figure 4 is a diagram of the conventional loop network system. FIG. 5 is a timing chart showing the operation of each station after a disconnection occurs in the loop type network system, FIG. 5 is a diagram corresponding to the claims of the present invention, and FIG. Flowchart showing the contents of processing executed at the station, No. 7
This figure shows the conditions for performing the reversal operation in each station, and FIG. 8 is a timing chart showing the operation after the detection of a disconnection in each station in the system of the same embodiment. A, B, C...Station, _L1 , _L2 , _L3 ...
...Transmission line, SLT3...Disconnection information slot, Pset
...Distance memory, 1...Switch circuit, 101...
...First means, 102... Second means, 103...
...Third means, 104...Fourth means.

Claims (1)

[Claims] 1. In a loop network system in which a plurality of stations are connected in a loop over a single transmission path to transmit communication data, each station transmits a signal from a preceding station in a predetermined communication direction. a first means for reversing the direction of transmission and reception by adding a position signal indicating the position of the station from the disconnection point to the communication data and reversing the direction of transmission and reception; and a first means for reversing the transmission and reception direction; When data is input, the position signal is changed to a position signal indicating the position from the disconnection point of the station based on the input position signal, and the position of the station indicated by the changed position signal is determined in advance. a second means for determining whether the station is an end station by determining whether the station is at the predetermined station position; a third means for reversing the transmission and reception direction after adding the changed position signal to the communication data and transmitting it; a fourth means for reversing the communication data, adding the changed position signal to the communication data and transmitting the communication data, and reversing the transmission/reception direction.