JP2000004243A - Data communication method for programmable controller and programmable controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten time for transmitting the data of an own station to an other station by shortening a data link scan time. SOLUTION: A 2-port RAM 20e is provided with an area for storing the number of times of last time sequence scan at present and the number of times of last time data link scan at present. For every time when the one sequence scan is finished, a sequence control part 30 increments the number of times of sequence scan at present and after the end of the one sequence scan, only on the condition of (number of times of data link scan at present) > (number of times of last time data link scan), link refresh is performed so that the number of times of last time data link scan is updated. For every time when one data link scan is finished, a data communication control part 20 increments the number of times of data link scan at present and after the end of the one data link scan, only on the condition of (number of times of sequence scan at present) > (number of times of last time sequence scan), the data of an own station are transmitted to an other station and updated the data to the number of times of last time sequence scan.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication method for a programmable controller and a programmable controller, and more particularly, to a data communication of a programmable controller for realizing distributed control such as line control and plant control by a programmable controller used for various controls. A method and a programmable controller.

[0002]

2. Description of the Related Art FIG. 6 shows a hardware configuration of a programmable controller (hereinafter sometimes abbreviated as PC) having a data communication function.

The PC1 to PCn stations are connected by a communication cable 50 for executing communication between the PCs. Each PC (PC1, PC2... PCn) 100
A data communication control unit 110 for controlling a data link; and a sequence control unit 1 for controlling execution of a sequence program and an input / output unit (not shown) to a connected control device.
20.

The data communication control unit 110 includes a CPU 110a for performing communication control, a serial control bus 110b for controlling a bus for executing communication, a ROM 110c for storing software such as a communication control system program, and the like. It is composed of a RAM 110d for storing link data received from the line under the communication control and link data to be transmitted to the line, and a two-port RAM 110e for interfacing with the sequence control unit 120.

[0005] The sequence control unit 120 includes a CPU 120a for sequence control and a ROM 120b for storing software such as a system program for sequence control.
A RAM 120c for temporarily storing the operation results and other information in the sequence program,
Input / output interface 1 for exchanging OFF information
20d and a memory 12 for storing a sequence program
0e.

[0006] FIG. 7 shows a PC, as shown in FIG.
(PCn, PC2,..., PCn) are connected to each other, and the transmission processing flow performed by the data communication control unit 110 of each station (PC of each station) in the local area network using the token passing method. Is shown.

First, each station determines whether or not the sequence scan of the sequence program has been completed (step S100). If the sequence scan processing has been completed (Yes at Step S100), the two-port RAM 110e of the data received from each station via the two-port RAM 110e in response to the refresh request.
, And data of each station and data to be transmitted to other stations based on the sequence program are sent from the sequence control unit 120 to the two-port RAM 110.
Then, a link refresh process of writing to e is performed (step S101). Note that the refresh request means that the CPU 120a of the sequence control unit 120
Is a command for requesting that the data in the inside be rewritten with data received from another station.

When the link refresh processing is completed, it is next determined whether or not the own station has obtained a token from another station (step S102). If the sequence scan processing has not been completed (No at Step S100), the link refresh processing is not performed.
Immediately, the token acquisition is determined (step S102).

If the token has not been obtained (No at Step S102), the process returns to Step S100 to check whether there is a refresh request. On the other hand, if the token has been acquired (step S
102)), the data to be transmitted to the other station is transferred from the 2-port RAM 110e to the serial control bus 1
10b (step S103).
The data and the token are transmitted to another station (step S104). When the transmission is completed, the process returns to step S100, and the above processing is repeated.

As for this type of transmission system, as shown in FIG. 7, the sequence controller 120 controls the two-port RAM 110e and the RAM 120e for each sequence scan.
c, transmitting and receiving the data stored in the 2-port RAM 110e of the own station to another station every data link scan.
No. 14,365, as disclosed.
In the scan transmission method disclosed in this publication, the stored data is divided into blocks, specific bits are provided for each block, and the stored data is transmitted to other stations only when the specific bits change due to rewriting of the stored data or the like. Is transmitted.

[0011]

In the data communication method shown in FIG. 7, the data link refresh is performed at the end processing after the end of the sequence scan, the token is received during the sequence scan, and the data stored in the own station is stored. Is sent to other stations,
Even when there is no change in the data, the data is periodically refreshed and transmitted, so that the load on the CPU and the load on the line increase, and efficient data communication cannot be performed.

In the scan transmission method disclosed in Japanese Patent Application Laid-Open No. 5-14365, only when a specific bit provided for each block of data stored in the own station indicates a change in data, that is, the local station information Only when the change has occurred, the own station information is transmitted to the other station, but the sequence controller does not determine whether the data communication controller has updated the other station information. The information is refreshed every time the sequence scan is completed. That is, refreshing between the sequence control unit and the data communication control unit is performed periodically even if there is no change in data, and there is a problem that a load is applied to the CPU accordingly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. A programmable controller which reduces the load on a CPU for data transmission, shortens communication time, and enables efficient data transmission. It is an object of the present invention to obtain a data communication method and a programmable controller.

[0014]

In order to achieve the above object, a data communication method for a programmable controller according to the present invention comprises a plurality of stations, and uses a token passing method to transmit data of the programmable controller in a local area network. In the communication method, an area for storing the number of current sequence scans and the number of previous sequence scans, and the area for storing the number of current data link scans and the number of previous data link scans are provided in a two-port RAM shared by each data communication control unit and the sequence control unit. The sequence control unit increments the current number of sequence scans each time one sequence scan ends, compares the current number of data link scans with the previous number of data link scans after the end of one sequence scan, and (current data link scan number)
Only in the case of> (previous data link scan times), the sequence control unit performs link refresh processing for reading data received from each station via the 2-port RAM and writing data to be transmitted to other stations to determine the current data link scan times. Stored in the previous data link scan count. The data communication control unit acquires the token, increments the current data link scan count each time one data link scan ends, compares the current sequence scan count with the previous sequence scan count after one data link scan ends, Only when “scan count”> (previous sequence scan count), the data of the own station is transmitted to another station, and the current sequence scan count is stored in the previous sequence scan count.

According to another aspect of the present invention, there is provided a programmable controller in a local area network using a token passing system, comprising a plurality of stations, the data controller having a data communication control unit and a sequence control unit. A 2-port RAM shared by the control unit and the sequence control unit is provided, and an area for storing the current sequence scan count and the previous sequence scan count, and the current data link scan count and the previous data link scan count is defined in the 2-port RAM. The sequence control unit increments the current number of sequence scans each time one sequence scan is completed, and after the completion of one sequence scan, the current data link scan count and the previous data link scan count. In comparison, only when (current data link scan count)> (previous data link scan count), the sequence control unit reads data received from each station via the 2-port RAM and writes data to be transmitted to another station by link refresh. The processing is performed to store the current data link scan count in the previous data link scan count, and the data communication control unit acquires a token, increments the current data link scan count each time one data link scan is completed, and After the link scan is completed, the current sequence scan count is compared with the previous sequence scan count, and only when (current sequence scan count)> (previous sequence scan count), the own station data is transmitted to another station, and the current sequence scan count is determined. The can count is for storing the previous sequence number of scans.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a programmable controller according to an embodiment of the present invention;

FIG. 1 shows a hardware configuration of a PC having a data communication function for implementing a data communication method according to the present invention. The PC1 station to the PCn station are connected by a communication cable 50, and communicate with each other on a local area network using a token passing method between the PCs, similarly to the conventional one. The PC 10 has a data communication control unit 20 and a sequence control unit 30.

The data communication control unit 20 includes a CPU 20a for controlling each unit of the data communication control unit 20, and a serial control bus 20 for controlling a bus for executing communication.
b, a ROM 20c for storing software such as a communication control system program, and an RA for storing link data received from the line, link data transmitted to the line, and the like.
M20d and a two-port RAM 20e for interfacing with the sequence control unit 30.

The sequence control unit 30 executes a sequence program and controls an input / output unit (not shown) of the PC 10.
And a ROM for storing software such as a sequence control system program.
30b, a RAM 30c for temporarily storing the operation result of the sequence program and other information,
An input / output interface 30d for exchanging N / OFF information, and a memory 3 for storing a sequence program
0e.

The two-port RAM 20e is shared by the data communication control unit 20 and the sequence control unit 30, and includes a current sequence scan count, a previous sequence scan count, a current data link scan count, and a previous data link scan count. The number of scans storage area 20f is defined by four memory areas for storing the number of times.

The data communication control unit 20 increments the current data link scan count in the scan count storage area 20f every time one data link scan is completed. The sequence control unit 30 increments the current number of sequence scans in the scan number storage area 20f every time one sequence scan ends.

The data communication control unit 20 obtains the token and, after completing one data link scan,
After incrementing the current data link scan count stored in the scan count storage area 20f of 0e, the current sequence scan count is compared with the previous sequence scan count, and when (current sequence scan count)> (previous sequence scan count) Only in this case, the data of the own station is transmitted to another station, and the current sequence scan number is stored in the memory area of the previous sequence scan number. As a result, the previous sequence scan count is updated.

The sequence control unit 30 has a two-port RAM of the data communication control unit 20 after one sequence scan is completed.
After incrementing the current sequence scan count stored in the scan count storage area 20f of 20e, the current data link scan count and the previous data link scan count are compared, and (current data link scan count)> (previous data link scan count) Only in the case of (2), link refresh is performed by reading data received from each station and writing data to be transmitted to other stations via the 2-port RAM 20e, and the current data link scan count is set to the memory area of the previous data link scan count. To be stored. As a result, the previous data link scan count is updated.

By the above-described series of processing, the data communication control unit 20 transmits the data of the own station to the other station only when one sequence scan is completed by the sequence control unit 30 and the data of the own station is updated. Is transmitted, and the sequence control unit 30 takes in data from another station only when one data link scan is completed in the data communication control unit 20 and data in another station is updated. As a result, the data communication time is reduced, and efficient data transmission becomes possible.

FIG. 2 shows a data communication control processing flow in the local area network. First, the current number of sequence scans and the number of data link scans are initialized to 0 (step S11).
Next, it is checked whether a token has been obtained (step S12). If the token has not been acquired (step S
(12 No), the process jumps to step S22.

If the token has been acquired (step S1)
(2 Yes) It is checked whether one data link scan has been completed (step S13). If one data link scan has not been completed (No at Step S13), this means that all the data of the other stations have not been received. In this case, Step S21 is performed without incrementing the current data link scan count. Jump to In step S21, only the token is transmitted to another station.

If one data link scan has been completed (Yes at step S13), it is determined that all data of the other stations have been received, and the current data link scan count is incremented (step S14). It is stored in the storage area 20f (step S15).

Subsequently, the current sequence scan count stored in the scan count storage area 20f of the two-port RAM 20e of the data communication control unit 20 is compared with the previous sequence scan count (step S16). Here, if (current sequence scan count)> (previous sequence scan count) is not satisfied (No at step S16), it means that the sequence scan has not been completed and the data to be transmitted is old. Is
The process jumps to step S21 to transmit only the token to another station (step S21).

On the other hand, if (current sequence scan frequency)> (previous sequence scan frequency) (Yes at step S16), it means that the sequence scan has been completed, that is, the data to be transmitted is the latest. In this case, subsequently, the data to be transmitted to the other station is transferred from the two-port RAM 20e to the serial control bus 20b (step S17), and the data of the own station is transmitted to the other station from the serial control bus 20b (step S17). Step S18).

After the data transmission is completed, the previous sequence scan count is updated to the current sequence scan count (step S19), and the updated last sequence scan count is updated to the scan count storage area 20f of the 2-port RAM 20e.
(Step S20).

In step S22, it is checked whether the data communication control unit 20 has been reset. If the data communication control unit 20 has been reset, the process returns to step S11. If not, the process returns to step S12.

FIG. 3 shows a sequence control processing flow in the local area network. First, the current number of sequence scans and the number of data link scans are initialized to 0 last time (step S31).

Next, it is checked whether one sequence scan has been completed (step S32). If it has not been completed (No at Step S32), this means that the data of the own station is old, and Step S39 is performed without incrementing the current number of sequence scans.
Jump to

On the other hand, if one sequence scan has been completed (Yes at step S32), this means that the data of the own station is the latest. In this case, the current number of sequence scans is incremented (step S33). ), And stores the data in the scan count storage area 20f of the two-port RAM 20e (step S3).
4).

Subsequently, the current data link scan count stored in the scan count storage area 20f of the two-port RAM 20e of the data communication control unit 20 is compared with the previous data link scan count (step S35). Here, if (current data link scan count)> (previous data link scan count) is not satisfied (step S27)
No), meaning that the data link scan has not been completed and all data has not been received. In this case, the process jumps to step S39.

On the other hand, if (current data link scan count)> (previous data link scan count) (Yes at step S35), it means that the data link scan has been completed and all data has been received. In step S36, a link refresh process is performed on the RAM 30c via the two-port RAM 20e.

After the link refresh processing is completed, the previous data link scan count is updated to the current data link scan count (step S37), and the updated last data link scan count is stored in the scan count storage area 20f of the two-port RAM 20e (step S37). S38).

In step S39, it is checked whether or not the sequence control unit 30 has been reset. If the reset has been performed, the process returns to step S23. If not, the process returns to step S24.

FIGS. 4A and 4B show station Nos. Of the data link system constituted by two stations. 1 and No. 2 is a time chart in which a horizontal axis represents a sequence scan and a data link scan.
The condition in the time chart in this example is: sequence scan (PC1) <data link scan 1 <sequence scan (PC2). (A) shows a case according to the present invention, and (b) shows a conventional example.

4 (a) and 4 (b), "4A" is a transmission / reception time including tokens and data of PC1 and PC2, "4B" is a transmission / reception time of only tokens of PC1 and PC2, and "4C". Are the token and data transmission time of PC1, the token and data reception time of PC2, the token transmission time of PC2 and the token reception time of PC1, "4
D ″ is the transmission time of the token of PC1, the reception time of the token of PC2, the transmission time of the token and data of PC2, and P
The C1 token and the data reception time are shown. “4N” to “4U” illustrate the flow of transmitting data to the PC 2 at a timing after the PC 1 is refreshed.

In the case of the conventional token passing method, the station No. 1, No. 2 always transmits all the data stored in the 2-port RAM when the token is acquired, so that transmission / reception of patterns other than “4A” is not performed.

"4E" to "4M" are timings for performing link refresh from the sequence control unit. Conventional PCs 1 and 2 transmit refreshed data to each station at timings "4E" to "4M".

Taking the PC1 side as an example, data refreshed at "4F" is transmitted to PC2 by data link scan of "4A"# 3, and data is reflected on PC2 by "4L" refresh. ("4O" is a line showing the timing). The data refreshed at “4E” is transmitted to the PC 2 by the data link scan of “4A” # 2, but is overwritten with the refreshed data at the timing of “4F”.
(“4N” is a line showing the timing).

Similarly, the data refreshed by “4H” is transmitted to PC2 by the data link scan of “4A” # 5, and the data is reflected on PC2 by “4M” refresh (“4Q” is changed to “4H”). This is a line showing the timing). The data refreshed by “4G” is transmitted to the PC 2 by the data link scan of “4A” # 4, but is overwritten by the refreshed data at the timing of “4H”, so that the data is reflected on the PC 2. (“4P” is a line showing the timing).

On the other hand, in the data link scan according to the present invention, when the data communication control unit 20 acquires the token, the station No. 1, No. If one data link scan, which is the transmission condition of the second data, is completed and the condition of (current sequence scan frequency)> (previous sequence scan frequency) is not satisfied, data transmission processing is not performed.

The data link scans satisfying the conditions at this time are "4B", "4C"# 1, "4C"# 2, "4C".
C "# 3," 4C "# 4," 4D "," 4B "does not transmit data to both PC1 and PC2, and" 4C "# 1 to # 4C.
"4C"# 4 is when PC2 does not transmit data, and "4D" is when PC1 does not transmit data. Taking the PC1 side as an example, the data refreshed in “4E” is transmitted to PC2 by the “4C” # 1 data link scan, and the data is reflected in PC2 by “4K” refresh (“4R”). Is a line showing the timing).

Similarly, the data refreshed by “4F” is transmitted to PC2 by the “4C” # 2 data link scan, and the data is reflected on PC2 by “4L” refresh (“4S” is changed to “4S”). This is a line showing the timing). The data refreshed by “4G” is transmitted to the PC 2 by the data link scan of “4C” # 3, but is overwritten by the refreshed data at the timing of “4H”, so that the data is reflected on the PC 2. (“4T” and “4U” are lines illustrating timing).

FIGS. 5A and 5B show station Nos. Of a data link system constituted by two stations. 1 and No. 2 is a time chart in which a horizontal axis represents a sequence scan and a data link scan.
In this example, the condition in the time chart is as follows: sequence scan (PC1)> data link scan 1 <
This is a sequence scan (PC2). 5A shows a case according to the present invention, and FIG. 5B shows a conventional example.

Also in FIGS. 5A and 5B, "4A"
Is the transmission and reception time including the tokens and data of PC1 and PC2, "4B" is the transmission and reception time of only the tokens of PC1 and PC2, and "4C" is the transmission time of the token and data of PC1 and the reception of the token and data of PC2. Time, PC2 token transmission time, PC1 token reception time,
“4D” indicates the transmission time of the token of PC1, the reception time of the token of PC2, the transmission time of the token and data of PC2, and the reception time of the token and data of PC1. Also, “4N” to “4V” illustrate the flow of transmitting data to PC2 at what timing after PC1 refreshes.

In the case of the conventional token passing method, the station No. 1, No. 2 always transmits all the data stored in the 2-port RAM when the token is acquired, so that transmission / reception of patterns other than “4A” is not performed.

"4E" to "4M" are timings for performing a link refresh from the sequence control unit.

The conventional PCs 1 and 2 are “4E” to “4E”.
The refreshed data is transmitted to each station at the timing of "M".
The data to be refreshed with “K” is “4A”.
The refresh data of E "is reflected (4N is a line showing the timing).

The data refreshed by "4L" reflects the refresh data of "4F" transmitted to the PC 2 by the data link scan of "4A"# 6 (4Q is a line showing the timing). is there). The data refreshed in “4E” is “4A” #
4 is sent to PC2 in the data link scan,
Since the data is overwritten with the refreshed data at the timing of “4F”, it is not reflected on the PC 2 (4
O is a line showing the timing).

The data transmitted at the timing of "4E" at "4P" is the same as the data transmitted at the timing of "4Q", and wasteful transmission is performed. The data refreshed by "4G" is transmitted to the PC2 by the data link scan of "4A"# 7, and the data is reflected on the PC2 by the refresh of "4M"("4R" is a line showing the timing). ).

In the data link scan according to the present invention, when the data communication control unit 20 acquires the token, the station No. 1, No. If one data link scan, which is the transmission condition of the second data, is completed and the condition of (current sequence scan frequency)> (previous sequence scan frequency) is not satisfied, data transmission processing is not performed.

The data link scans satisfying the conditions at this time are “4B”, “4C” # 1, “4C” # 2, “4C”.
C "# 3," 4C "# 4," 4D "," 4B "does not transmit data to both PC1 and PC2, and" 4C "# 1 to" 4C "# 4 does not transmit data to PC2. , “4D”
Is a case where the PC 1 does not transmit data.

To describe the PC1 side as an example, data refreshed at "4E" is transmitted to PC2 by data link scan of "4C"# 1, and data is reflected on PC2 by "4K" refresh. ("4S" is a line showing the timing).

Similarly, the data refreshed by “4F” is transmitted to PC2 by the data link scan of “4C” # 2.
Is transmitted to PC2 by refreshing “4L”.
(“4T” is a line showing the timing). Note that the data refreshed by “4G” is transmitted to the PC2 by the data link scan of “4C” # 3.
However, since it is overwritten with the refreshed data at the timing of “4H”, it is not reflected on the PC 2 (“4S” and “4T” are lines showing the timing).

As a result, the time per one data link scan can be reduced, and the time from when a link refresh request is issued by the sequence control unit 30 to when the data of the own station is transmitted to each station is also reduced. Data processing efficiency can be improved.

[0060]

As can be understood from the above description, according to the data communication method of the programmable controller according to the present invention, the sequence control section increments the current number of sequence scans every time one sequence scan is completed, and Only when [link scan count]> (previous data link scan count), link refresh is performed, the current data link scan count is stored in the memory area of the previous data link scan count, and the data communication control unit acquires a token. Each time one data link scan is completed, the current data link scan count is incremented, and only when (current sequence scan count)> (previous sequence scan count), the own station data is transmitted to the other station, and the current sequence scan count is set. Number of scans Since the data is stored in the memory area of the number of previous sequence scans, the sequence scan time and the data link scan time can be reduced, and the effect of transmitting the data of the own station to other stations can be reduced. .

According to the programmable controller of the next invention, the two-port RAM shared by the data communication control unit and the sequence control unit is provided.
Defines an area for storing the current sequence scan count and the previous sequence scan count, the current data link scan count and the previous data link scan count, and the sequence control unit increments the current sequence scan count each time one sequence scan ends. Link refresh is performed only when (current data link scan count)> (previous data link scan count), and the current data link scan count is stored in the memory area of the previous data link scan count. Is acquired, and the number of current data link scans is incremented every time one data link scan is completed. Only when (current sequence scan frequency)> (previous sequence scan frequency), the data of the own station is transmitted to another station. Since the current sequence scan count is stored in the memory area of the previous sequence scan count, the sequence scan time and the data link scan time can be reduced, and the time for transmitting the data of the own station to other stations can be shortened. The effect that it can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a hardware configuration of a PC having a data communication function for implementing a data communication method according to the present invention.

FIG. 2 is a flowchart showing a data communication control process in the data communication method according to the present invention.

FIG. 3 is a flowchart showing a sequence control process in the data communication method according to the present invention.

FIG. 4 is a time chart showing timings of a sequence scan and a data link scan. (The condition in the time chart is sequence scan (PC1) <
Data Link Scan 1 <Sequence Scan (PC
2))

FIG. 5 is a time chart showing timings of a sequence scan and a data link scan. (The condition in the time chart is sequence scan (PC1)>
Data Link Scan 1 <Sequence Scan (PC
2))

FIG. 6 is a block diagram showing a hardware configuration of a conventional PC.

FIG. 7 is a flowchart showing a data communication control process in a conventional PC.

[Explanation of symbols]

10 PC, 20 data communication control unit, 20a CP
U, 20b Serial control bus, 20c RO
M, 20d RAM, 20e 2-port RAM, 20f
Scan count storage area, 30 sequence control unit,
30a CPU, 30b ROM, 30c RAM, 3
0d I / O interface 30e memory.

Claims (2)

[Claims] 1. A data communication method for a programmable controller in a local area network comprising a plurality of stations and using a token passing method, comprising: a current sequence scan count and a previous sequence scan count; and a current data link scan count and a previous data link count. An area for storing the number of scans is provided in a two-port RAM shared by the data communication control unit and the sequence control unit.
The current sequence scan count is incremented, and after the completion of one sequence scan, the current data link scan count is compared with the previous data link scan count. Only when (current data link scan count)> (previous data link scan count), the sequence control unit is executed. Performs a link refresh process of reading data received from each station via the 2-port RAM and writing data to be transmitted to another station, and stores the current data link scan count in the previous data link scan count. Token is acquired, the number of current data link scans is incremented each time one data link scan is completed, and the number of current sequence scans is compared with the number of previous sequence scans after one data link scan is completed. The data communication method of the programmable controller, wherein the data of the own station is transmitted to the other station and the current number of sequence scans is stored in the number of previous sequence scans only when (number of sequence scans)> (number of previous sequence scans). . 2. A programmable controller in a local area network comprising a plurality of stations and using a token passing method, comprising: a data communication control unit; and a sequence control unit, wherein the data communication control unit and the sequence control unit A two-port RAM that is shared between the two-port RAM and defines an area for storing the current sequence scan count and the previous sequence scan count, and the current data link scan count and the previous data link scan count in the two-port RAM; Increments the current number of sequence scans every time one sequence scan is completed,
After the completion of one sequence scan, the current data link scan count is compared with the previous data link scan count. Only when (current data link scan count)> (previous data link scan count), the sequence control unit receives each data link via the 2-port RAM. A link refresh process for reading data received from a station and writing data to be transmitted to another station is performed, and the current data link scan count is stored in the previous data link scan count. Each time a data link scan is completed, the current data link scan count is incremented, and after one data link scan is completed, the current sequence scan count is compared with the previous sequence scan count, and (current sequence scan count)> (previous sequence scan count) A programmable controller which transmits the data of its own station to another station only when the number of times of scanning is the same, and stores the current sequence scanning number in the previous sequence scanning number.