JPS58127447A - Data transmission method - Google Patents

Abstract

PURPOSE:To simplify the procedure at the transfer of a master station, by bringing a moving contact of a changeover switch of a slave station for a prescribed time into contact with a fixed contact of other slave stations and taking a slave station which can receive a message before the prescribed is elapsed as the master station. CONSTITUTION:The 1st message is transmitted to controllers C2-Cn from a controller C1. With the 1st message, moving contacts Sc2-Scn of changeover switches SW2-SWn of the controllers C2-Cn are bronght into contact with other fixed contacts SB2-SBn for a prescribed time. The 2nd message is transmitted from the controller C1 to the controllers C2-Cn before the prescribed time is elapsed, and the controller C2 which can receive this 2nd message becomes a new master station.

Description

[Detailed description of the invention]

The present invention relates to a data transmission method. In a system that performs digital control using multiple digital control devices, it is recommended not to fix the master station because controlling the master station by fixing it may cause the entire system to go down due to a malfunction of the master station. A data transmission method is often adopted in which each digital control device in the system can act as a master station. In the conventional data transmission method, as shown in FIG.
The receiving terminal RX11 and the transmitting terminal TI TXn of C engineering~CCr1 are transmitted via input amplifiers AR□~ARゎ and output amplifiers AT□~ATn, respectively.
In those commonly connected to L1, one of the plurality of controllers C to Cn, for example, controller C1, is the master station, and the remaining p controllers C2 to Cr1 are the slave stations, and only between the master station and the slave stations. When mutual transmission of digital data is performed and the master station controller C□ no longer needs to request data from the slave stations controllers C2 to Cn, the controller C changes to the controllers C2 to Cn.
Sequential inquiries to Cn as to whether it is necessary to break up the relationship 1. When the destination of the inquiry needs to become the master station and the destination requests the controller C for the right to become the master station. , Controller C transfers the right to become the master station to the contact, and if no contact requests the right to become the master station, the controller C transfers the right to become the master station. -RaCyo holds the right to become RJfi6. For example, controller C makes an inquiry to controller C2. When the controller C2 requests the right to become a weir station from the controller C, the controller C transfers the right to become a master station to the controller C2. However, in this data transmission method, when the master station moves, it always makes inquiries to the slave stations, requests for rights from the slave stations, and
It is necessary to transmit data such as handing over to the station, and consideration must be given to the slave stations that have not been inherited.The procedures when transferring the R station are complicated, and the procedure for transferring the R station is complicated. Processing during transfer takes a lot of time, data transmission efficiency is low, and responsiveness is particularly low in digital control devices that require real-time performance. Therefore, an object of the present invention is to provide a data transmission method that can simplify the procedure for transferring a broken relationship, shorten the transfer processing time, and improve data transmission efficiency. An embodiment of this invention is shown in FIGS. 2 to 10,
, -ff: In other words, this data transmission method has the function of controlling the process according to a predetermined control algorithm as shown in Figure 1iR2, and also has the function of controlling data transmission. Yo~CCn receiving terminal R
Changeover switch SW for X engineering to RXn. One of the fixed contacts SA to SAn is connected to the transmitting terminals TXI to T of the controller body CC1 to CC.
The other fixed contact S of the changeover switch SW to Xn5n
B~SBn are connected to multiple controllers C~Cn
One of the fixed contacts SA□ to SAn and the movable contact S of each of the changeover switches SW to SWo. □ to Son are sequentially inserted in series in a loop-shaped transmission line L2, and one of the plurality of controllers C to Cn is used as a master station, and the rest of the plurality of controllers C to CD are As a slave station, data is transmitted between the master station and the slave station. In addition, the plurality of controllers C1 to CD normally have movable contacts S as respective changeover switches SW□ to SWo. ,~Sor
] is brought into contact with one of the fixed contacts SA-SAo, and the movable contact S of the change-over switch 5w-5w is used only when a signal is sent. □〜S
on to the fixed contact of the external power controller n, and transmit the message (message of releasing the master station) from the master station, %J, to the controller C, to all the slave stations, ie controller C). o-ra C2 to Cn, and by this message, all the slave stations, that is, the movable contacts SC2 to Soo of the changeover switches SW2 to SWo of the controllers C2 to CD are switched to the other fixed contacts SB2 to 5BnVc-B2. The master station is brought into contact with the master station for only a certain period of time, and then the master station is contacted with the master station before a certain period of time has elapsed. That is, controller C sends a second message (token message) to all slave stations, that is, controllers C2 to Cn: The slave station that was able to receive this second message, that is, controller C2, becomes the new master station. It is characterized by becoming. Let me explain in more detail. When controller C1 is the master station and controllers C2 to Cn are slave stations, the state in FIG. 2 is as follows.
Controller C, which is the master station, needs information held by controller C, which is the slave station. The controller C is requesting data from the controller Cn, and only the changeover switch SW is the movable contact S. , is in contact with the fixed contact SB□. The state in FIG. 3 shows the state in which controller C is sending a response message to the above request. Only the changeover switch SWn is a movable contact S. Fixed dipping of n,
5BflK is in contact. In the state shown in Figure 4, controller C□ does not need to be the master station, and controllers 02 to C
First message to n (message of letting go of the breakup)
It shows the state in which it is sending a signal, and only the changeover switch SW is the movable contact S. 1 is in contact with the fixed contact SB. In the state shown in FIG. 5, controllers C2 to C receive the first message from controller C and selector switch S
Movable contacts S of W2 to SWn. 2~50nt fixed contact S
2nd B2 from controller C by touching -8
Waiting for the message (token message) of Bn, :y indicates that only controller C2 has received the message of tIg2 when controller C sends the second message, in this case, it sends the second message. The controller 02 crab that was able to receive it will be a new catastrophe. Note that if the controller C2 does not need to become the master station, the controller C2 operates in the same manner as described above and changes the master station to the controller C.
Move to 3. With this configuration, the master station 10-RA C can be transferred to the master station without making any inquiries to the slave stations that are not connected to the line. If only controller C is connected in the line, as shown in FIG. 6, when controller C sends the second message. Controller C itself receives O's wI2 message, and it can be seen that nothing has been inherited. Data transmission between controllers 10-10-10-Cn is as follows. A start-stop synchronization method of 1 lbit/frame is used as the formant. The frame consists of a 1-bit star 1 as shown in Figure 7.
Bit S

[, 8-bit data bit b. ~b 1-bit header bit h (message 7
It consists of a 1-pin stop bit sp), and a 1-pin stop bit sp. Me, 7. 10-no (-11 For example, as shown in the 8th section i,
The transmission destination 71 consists of a block consisting of a address, control data, source address, number of data bytes, data 1 to data n, and a check code, and the destination address, etc. are all constructed from the frame shown in FIG. Only the destination address frame is Henogu Pinto ht-“l
” to indicate the beginning of the block. The destination address indicates the destination of the message block. The control data is written with data for performing various types of control. The source address indicates the source of the message block. The number of data bytes indicates the number of binary data shown below. The check code is for detecting errors.5 Specific data transmission operations will be explained with reference to the time charts of FIGS. 9' and 10. When controller C is a master station and needs data from controller C to be transmitted at a slave station, controller C1 sends a message M as shown in FIG. 9 to controller Cn.
Send (some kind of data g! message). After this, the controller C7 sends the data back to the controller C7 with the message M2 shown in Fig. 9 above.Switch switch when 0, -h 5W1゜sw, #-t
Movable contact S only when sending a message. l, SC! n is brought into contact with the fixed contact SB□' SBn. After this, when the controller C□ no longer needs to be the master station, the controller C□ sends a message M3 to the controllers C2 to Cn to release the master station as shown in Figure 1g10.
Send to all (global address). Core for this message M3) a-poor c2~c
n brings the movable contacts sC2 to So of the changeover switches SW2 to SWn into contact with the fixed contacts ``B2 to SBn'' within 13 hours, and holds that state for a certain period of time T. Meanwhile, the controller C sends a message M3. Next, after T2 time has elapsed, a token message M, '!i-T, is sent to all controllers 02 to Cn (global address). In this case, controller C1 sends a token message M.
4, transmission period T, only the changeover switch SW's movable contact S
Contact the fixed contact SB□. Here, if T21 is T3 and T2+T4<T3+T, token message M4 is received by the receiving station, so only controller C2 can receive token message M4, and controller C2 becomes the master station. and sends message M5. If only controller C is connected to the line, no station will receive token message M4,
Returning again to controller C, controller C□ shows that no other station has succeeded. In this way, in this embodiment, for example, control a is transmitted from the master station.
~ Send message M3 to separate the master station from C1,
By this message M3, controller 5C, which is a slave station,
The movable n contacts S.2-Son of changeover switch SW2-S of -C are brought into contact with the fixed contacts SB2-5BnK, and in this state, controller C sends token messages M, t-, and receives this token message M4. Since the controller C2 that has been transferred is set as the new master station, there is no need to know the addresses of the slave stations that have not succeeded to the MK when the failure leaves the master station.There is also no need to make inquiries to the slave stations. This simplifies the procedure when transferring the parent station, reduces the time required for processing when transferring the parent station, and improves data transmission efficiency.Another embodiment of the present invention is shown in FIG. 13. That is, this data transmission method responds to the first message from the controller C. Among the controllers C2 to Cn, the changeover switches SW2 to SWn of the controllers that need to become the master station are moved. Contact point S., ~
Soo is made to touch the fixed contacts SB2-5BnKIiI to wait for the second message from the controller C3. The rest is the same as the previous embodiment. In the state shown in FIG. 11, the controllers C2 to cn receive the first message from the controller C, and among the controllers C2 to Cn, the changeover switches sw3 to swn of the controllers 03 to Cn, which are required to become master stations, are activated. Movable contact S. 3-Soo are brought into contact with fixed contacts SB3-5BnK to wait for the second message from controller C□, and when controller C□ sends the second message, only controller C3 receives this second message. In this case, the controller C3 that was able to receive the second message becomes the new master station. In addition, controller C2-, which does not need to be a master station (token messages will be input, but this controller C2 is configured in software so that it does not receive token messages. In this way By configuring a trap, the controller C can transfer the master station without making inquiries to the slave stations that are not connected to the line and need to be broken.Note that any slave station within a line If the slave station does not need to become the master station, the 1g2 message sent from controller C returns to controller C again, as shown in Figure 912, requesting that any slave station become the master station. There is no controller C, 5', in this case,
The above procedure may be performed again after a while. The specific movement of data transmission will be explained with reference to the time chart of FIG. 13. Normal data transmission is similar to the previous embodiment. Thereafter, when the controller C no longer needs to be the master station, the controller C□1 intercepts the message M3 to release the R station from the pan of the controllers C3 to Cn (global address). The controllers c3 to C, which need to become master stations for M3, must switch switch SW3 to SW within 13 hours! 1 movable contact So3~
Soo is brought into contact with the fixed contacts SB3-5BnK, and this state is maintained for a certain period of time T. On the other hand, controller C sends a token message M, 12 hours after sending message M3! kT, controller C2 during time
~Cn (global address). In this case, controller C is token safe M
4 transmission period T4 only, the movable contact S of the changeover switch SW
. Contact the fixed contact SB. Here, T2>T
3 and T2+T4<T3+Te, the token message M4 is received by the receiving station. Only the controller C3 can receive the talk/message M4, and the controller C3 becomes the master station and transmits the message M5. In this embodiment, the changeover switches SW3 to SW of the slave stations that need to become the master station in response to the first message from the master station are
n movable contact S. 3~Son only fixed contact SB3~SB
This makes it possible to further improve the efficiency of data transmission, compared to the previous embodiment in which the master station is sequentially transferred to slave stations that do not need to become R stations. can. As described above, the data transmission method of the present invention is as follows. This has the effect of simplifying the procedure for transferring a broken relationship, shortening the transfer processing time, and increasing data transmission efficiency. Next, the first disclosed technique will be explained. Figure 914 shows a block diagram of a conventional serial data transmission system, in which PC□ to PC, H are control terminals, and L3 is a serial data transmission line. Serial data transmission between the input I-N of the control terminals PC~PCn and the output OUT of the control terminals PC3~PCn and PC respectively. Connected in a loop with AL3. FIG. 15 is a block diagram showing the internal configuration of each of the control terminals PC to PCn, and includes a serial data receiving section RR1.
Next, the received data is converted into parallel data by a serial-to-parallel converter Cv, read by the control unit CR, and again converted into serial data by a parallel-to-real converter Cv2, and sent from the serial data transmitter π. Transmission line L
It is set to be sent out on 3rd. However, in such a conventional serial data transmission system, the time required to convert serial data into parallel data, the time to read parallel data kR, the time to write parallel data to parallel-to-serial converter CV2, and the time required to convert parallel data to serial data and convert it into serial data Data transmission 1sL
The entire time for sending data in step 3 is the transmission delay time. Also,
There was a problem that if even one of the control terminals PCU to PCn went down, serial data could no longer be transmitted and the entire system would go down, resulting in low reliability. FIG. 16 is a block diagram showing the configuration of a control terminal that can increase the data transmission speed and improve the reliability of the system. In the figure, L3 is a serial data transmission line consisting of an electric wire for transmitting electrical signals or an optical fiber for transmitting optical signals, RR1 is a serial data transmission line, and converts the signals of , , etc. to the internal IC signal level. and import/Real data receiving section, T
T is a serial data transmitter that sends serial data to the serial data transmission line L3, and serial data receiver i
The output of RR is connected to the serial-to-parallel converter CV and one input end of the signal switching unit SS.
The other input terminal of S is connected to the output of the parallel-to-serial conversion section CV2, and the output of this signal switching section SS is connected to the input terminal of the serial data transmission section. Signal switching section SS
consists of a relay coil RY and its relay contact "y", and is connected to the control section CR1 or the parallel-serial conversion section C■2.
It is controlled by the output of the monostable multi-pibra pMM1 which is controlled by the start signal from. Note that serial data can be sent and received using the IIA step synchronization method. Next, we will explain the operation. First, when serial data is sent, the signal is converted to an internal IC signal level by the serial-data receiving unit RR, and is read as data by the 1-control unit CR via the serial-parallel converter C. 1 and the signal switching unit SSK enters. Since the Q output of the monostable multivibrator MM is off and no current is flowing through the relay coil RY, the signal switching unit SS is
+7 L batch point ry switches to NC@ (NC-C0M
), the signal sent from the serial data receiving section RR is sent as is to the serial data transmitting section Yoi,
From there it is sent to an external serial data transmission IIL3. In this case, while the control section CR reads the serial data sent thereto, the serial data is sent out from the serial data transmission section without any delay. Next, when the serial data is sent from the outside and is sent from the control unit CR itself, the control unit CR outputs a start signal to start the monostable multivibrator MM, and its Q output is turned on. and relay coil RY
Apply current to the relay contact ry and switch it to No@ (No
-C0M), then the parallel data is supplied from the control unit CR1 to the parallel-serial converter Cv2, and a serial signal is output from the parallel-serial converter Cv2, and is sent to the serial data transmitter ■ through the signal switching unit SS, and from there External serial data transmission! Sent to 1L3. At this time, the monostable multivibrator MM□ is activated by the start signal and the time it takes to return to the original state is set to be slightly longer than the time it takes to send out 1 data of 7 real data in the asynchronous system, and the control unit CR When one data of serial data sent from YO is completed, the Q output of the monostable multivibrator MM automatically turns off, the current in the relay coil RY disappears, and the relay contact RY becomes N.
C@ (, NC-C0M), and the output side of the serial data receiving section RR is connected to the input end of the serial data transmitting section. In this way, when the control unit CR sends out serial data, F! Be sure to activate the monostable multivibrator MM for each piece of data and switch the signal switching section S.
S is switched to the data side from the control unit CR, and then serial data is sent out. As a result of this configuration, when the control unit CR reads data, the data can be transmitted to the serial data transmission line L3 with almost no delay. Further, even if some of the control terminals PC to PCn go down due to a runaway of the microcomputer or the like, serial data transmission continues, and the entire system does not go down, thereby increasing reliability. In FIG. 17, the signal switching section SS in FIG. 16 is configured with an IC gate instead of being configured with a relay, and the other configuration is the same as that in FIG. 16. In Figure 17, the Q output of the monostable multi-pie break MM is off,
That is, in the rHJ state, the output from the upper gate G is sent to the serial data transmitting section H□, and the serial data from the control section CRY is not transmitted. On the other hand, when the Q output of the monostable multivibrator MM□ is on, that is, in the rLJ state. The output of the upper gate G is in a high impedance state, and the output of the lower gate G2 is in a conductive state. In other words, serial data from the control section CR□ is sent to the serial data transmitting section RR, and the serial data is sent to the serial data receiving section RR.
Data from outside will not be transmitted. In addition, INIF! It is an inverter. In the case of Fig. 36, the monostable multivibrator MM was started by directly outputting the start signal from the control unit CR□, but when the switching speed of the signal switching unit SS is fast as shown in Fig. 17, parallel serial The output of the converter Cv2 is connected to the monostable multivibrator MM, and it also serves as the start signal for the monostable multivibrator MM.
The start signal from the machine can be eliminated. That is, when data is sent in the asynchronous method, the start bit of rLJ is always outputted first as shown in Figure 18, so the falling edge of this start bit causes the monostable multivibrator MM to switch to the 18th bit. Just start it up as shown in Figure CB). In addition, Figure 18 shows the serial data.
) in Figure 8 is a monostable multivibrator! It shows the Q output of M. Next, regarding the second disclosed technology, Figures 19 to 23
This will be explained with reference to the figures. In general, a data transmission/reception system between a plurality of combinators generally takes the form shown in FIG. 919. As shown in FIG. When we want to send data, we will refer to the data transmission control unit 2. By doing this, it is also possible to compensate for the disadvantage that when the CPU section 3 is connected in series to the data transmission line 1 as shown in FIG. 21, unnecessary data must also be input to the CPU section 3, which takes time. can become. However, in the data transmission/reception system shown in FIG. 20, a problem occurs when the CPU section 3 refers to the state of the data transmission path 1. The situation is shown in FIG. In other words,
If we look at the state of the data transmission path 1 when the CPU section 3 is in AA mode, we will see that data is present on the data transmission path 1 at this time. In a case like BB, even though there is data, the level is "0", so it is determined that there is no data, and as a result, data is output to data transmission path l, Data collision occurs. In order to avoid this, the CPU section 3 inspects the data transmission path l at regular intervals,
There is a way to check the presence or absence of data, but this is extremely inefficient. Not the best method. Therefore, the purpose of what will be described below is to detect the presence or absence of data on the data transmission path l in order to efficiently perform two data transmissions. FIG. 23 is a block diagram for explaining a data transmission/reception system that can achieve the above purpose, and is a stable multivibrator MM2 between the data transmission line l and the three CPU parts.
The structure is such that . To explain the operation, when data is on the data transmission path l, determine the time constant using the capacitor C and resistor RA of the monostable multivibrator MM2 so that it continues to oscillate while the data is being input. 0'' level continues, and the Q output of monostable multivibrator MM2 is ``1''.9. The CPU section 3 can confirm the presence or absence of data on the data transmission path 1 without making a mistake. Note that SP is a changeover switch, which is switched to the upper side when receiving data, and switched to the lower side when transmitting data. The effect is that when checking the presence or absence of data on the data transmission path 1, the CPU section 3 can confirm the presence or absence of the monitor without making a mistake when only the output of the monostable multivibrator MM2 is required. Regarding the third disclosed technology, FIG. This will be explained with reference to FIGS. 24 and 25. -4. In a data transmission system between a plurality of computers, data transmission and reception is generally performed in a system as shown in FIG. 19. Possible flows related to data transmission include a case where the sender transmits data and then waits for a response from the receiver, and a case where the sender moves to the next sequence as soon as the data has been transmitted. Now, let us consider a case where the data transmission line 1 is disconnected or for some other reason it becomes impossible to send and receive data. In both cases, since there is no response even though data has been transmitted, the CPU section 3 will continue to wait forever. In the latter case, the sending side will assume that the data has been sent and move on to the next step, but the receiving side may not actually have received the data, so it may run without processing it. In either case, the system would be incomplete. The purpose of what will be described below is to notify the user when the data transmission line 1 is disconnected for some reason or when data transmission and reception becomes impossible due to other reasons. FIG. 24 shows the configuration of each unit in the system shown in FIG. 19, in which a disconnection detection section 4 and a display section 5 are added to the system shown in FIG. Figure 25 shows the specific circuit configuration of the disconnection detection section 4 and display section 5. 1MM3 is a stable multivibrator with a retrigger function, R is a resistor, and CBF
i Capacitor, LED is monostable multivibrator M
This is a light emitting element connected to M3. I will explain the operation in detail. If there is data input, the monostable multivibrator MM3 continues to oscillate, so the output Q becomes "1" and one light emitting element LED does not light up. In addition, since the monostable multivibrator MM3 is used with a retrigger function, it will continue to oscillate as long as the interval between data is within a certain time T determined by the time constant of resistor RB and capacitor CB, so one light emission will occur. The element LED does not light up. However, if you receive the data due to disconnection or other reasons,
If there is no input even after one hour, the stable multivibrator MM3 stops oscillating and the Q output changes to rOJ, so that one light emitting element LED lights up. Through the above-described operations, it is detected that there is no data input. The effect is that in systems that operate while transmitting and receiving data to each other, if data transmission and reception becomes impossible for some reason, such as a fault, one light-emitting element LED lights up to indicate the status to the user. This means that the user can take action against it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining a conventional data transmission method, FIGS. 2 to 6 are block diagrams for explaining an embodiment of the present invention, and FIG. 97 is a configuration diagram of frame data. , 538 is a diagram of the data structure of l block, % FIGS. 9 and 1θ are time charts for explaining data transmission), and FIGS. 11 and 12 are other 1j! A block diagram for explaining the embodiment, FIG. 13 is a time chart for explaining data transmission, FIG. 14 is a block diagram of a conventional example of the first disclosed technology, and FIG. M15 is a concrete block diagram of the main part thereof. Figure, Figure 6a First of the first disclosed technology
Specific block diagram of the main part of the improvement example, @ Fig. 17 d Specific block diagram of the main part of the second improvement example of the first disclosed technology, Fig. 18
(B) is a waveform diagram of each part, FIG. 19 is a block diagram of a conventional example of the second disclosed technology, FIGS. 20 and 21 are specific configuration diagrams of its main parts, and FIG. 22 is a signal waveform diagram thereof, FIG. 23 is a concrete block diagram of the main part of the improvement example of the second disclosed technology;
Figure 4 t'i Pronk diagram of an improvement example of the third disclosed technology, second
Figure 5 is a specific circuit diagram of the main part. C□~Cn...Controller, cc~CCゎ Controller body, SW~SWo...Switching switch section
Ward V Sunmine PCI Fig. 13 Fig. 14 US of MMl to TTl Fig. 18 Fig. 19 Fig. 2 Fig. 20 Start Data Strike No. 22
Illustration procedure amendment (voluntary) 1. Case Description Bp, No. 1157 Patent Application No. 012163
No. 2, Invention name data transmission method 3, Relationship with the case of the person making the amendment Applicant Address Osaka Prefecture Industrial Works! City Oaza Kadoma 1 troweling site name (
583) Matsushita Electric Works Co., Ltd. Representative sound Iku Kobayashi Spontaneous correction 6, catch 11', target F! Description A and drawing 7, contents of amendment (1) On page 9, line 12 of the specification, after the words "as a format", "for example" is added. (2) Page 23, line 14 of the specification, “Level r
The phrase "because of OJ" was corrected to "because of level 1". (3) Page 24, line 12 of the specification, “Even if the input is rO
Correct the phrase "J level" to "even if the input is '1'level". (4) Line 16 of the 27th summer of the specification, “Data configuration diagram”
The statement has been corrected to read "a configuration diagram showing an example of data." (5) On page 27, line 17 of the specification, the phrase "data structure diagram" is corrected to read "configuration diagram showing an example of data." Agent Patent attorney Akino Miyai

Claims (2)

[Claims] (1) One fixed contact of a changeover switch is connected to the reception terminal of a controller body that has a function of controlling processes according to a predetermined control algorithm and also has a data transmission control function, and the changeover switch is connected to a transmission terminal of the controller body. One fixed contact and the movable contact of each of the four changeover switches of the plurality of controllers connected to the other fixed contact are successively inserted in series in a loop-shaped transmission path, and one of the plurality of controllers is is used as a master station, and the rest of the plurality of controllers are used as slave stations to transmit data between the master station and the slave stations, and each of the plurality of controllers normally has a changeover switch with a movable contact and one fixed contact. The movable contact of the changeover switch is brought into contact with the fixed contact of the external force only when transmitting a signal, and the first message is sent from the master station to the
This first message causes the movable contacts of the changeover switches of all the slave stations to contact the other fixed contacts for a certain period of time, and before the specified period of time, the master station sends a message. A data transmission method in which the second message is sent to all slave stations, and the slave station that is able to receive this second message becomes the new master station. (2) One fixed contact of a changeover switch is connected to the reception terminal of a controller body that has a function of controlling processes according to a predetermined control algorithm and also has a data transmission control function, and the changeover switch is connected to a transmission terminal of the controller body. One of the fixed contacts and the movable contact of each of the changeover switches of each of the plurality of controllers to which the other fixed contact of 1NM, and the remaining t slave stations of the plurality of controllers transmit data between the master station and the slave stations, and the plurality of controllers each have a changeover switch, usually a movable contact A, as a single-power fixed contact. The movable contact of the changeover switch should be brought into contact with the other fixed contact only when sending a signal. A first message is sent from the master station to all slave stations, and this first message causes the movable contacts of the changeover switches of all the slave stations that need to become the master station to contact the other fixed contacts. , the R station transmits a second message to all the slave stations before the specified period of time elapses, and this second message is received among all the slave stations that need to become the master station. A data transmission method in which the created slave station becomes the new master station.