JPH06208408A - Master link system for programmable controller - Google Patents

Abstract

PURPOSE:To prevent a programmable controller (PC) from processing the same request command outputted from an application work program included in a master computer twice without using a complicated communication control procedure program by judging whether the transmission of a request command is resending or not, and in the case of resending, comparing a stored request command with the newly received command. CONSTITUTION:The PC 2 stores a request command processed just before and judges whether command transmission from the master computer 1 to the PC2 itself is resending or not by resending discriminating information added to a command format. In the case of resending, the PC 2 compares the stored request command with the newly received command. When both the commands are the same, the PC 2 informs that the command has been processed to the computer 1 by the result code of a response data format. Then the computer 1 aborts the resending of the command. Consequently the PC 2 can be prevented from processing the same request command outputted from the computer 1 twice.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a programmable controller host link system for controlling communication between a programmable controller and a host computer.

[0002]

2. Description of the Related Art In a programmable controller system, a programmable controller and a host computer are mutually linked by a host link system in order to execute application programs such as system monitoring by a host computer such as a personal computer and a minicomputer. It has been conventionally performed to establish a communicable connection.

RS is used as a transmission line interface for communication between the programmable controller and the host computer.
232C, RS422, etc. are used, and as a communication control procedure, a non-procedure method is widely used to reduce the load on the communication software of the host computer.

[0004]

The transmission of a function request (command) from the host computer to the programmable controller by non-procedural communication and the response (response) of the processing result of the programmable controller to the host computer are as follows. When a situation occurs in which the responder does not reach the application program of the host computer due to communication failure or the like, the command is generally retransmitted to the programmable controller by the time-over control by the application program.

In this case, the resend command is processed twice by the programmable controller, resulting in a problem that the request command from the application program is processed twice. This dual processing does not cause a problem when the host computer reads the status variables from the programmable controller, but causes a malfunction in the application system consisting of the host computer and the programmable controller when writing or changing data. become.

The present invention has been made by paying attention to the above-mentioned problems in the conventional programmable controller high-order link system, in which the programmable controller is high-ordered without requiring a complicated communication control procedure program. It is an object of the present invention to provide a programmable controller host link system having a processing function of preventing a request command from a computer application program from being processed twice.

[0007]

According to the present invention, an object of the above is to perform processing immediately before a programmable controller in a programmable controller host link system for controlling communication between a programmable controller and a host computer. Storage means for storing one request command is provided, and retransmission identification information is added to the command data format transmitted from the host computer to the programmable controller, and whether or not the command transmission from the host computer to the programmable controller is a retransmission by the retransmission identification information. If it is a resend, the request command stored in the storage means and a new received command are compared, and if they are the same, the programmable controller transmits to the host computer that it has already been processed. Notifies the host computer as a result code scan Pons data format, the host computer is accomplished by the programmable controller upper link system, characterized in that it is configured to stop the retransmission of the command.

[0008]

According to the programmable controller host link system of the present invention, one request command processed by the programmable controller immediately before is stored in the storage means, and is retransmitted by adding the command data format transmitted from the host computer to the programmable controller. Whether or not the command transmission from the host computer to the programmable controller is a resend is determined by the identification information, and if the request command stored in the storage means and the new received command are the same at the time of resending, The fact that the processing has already been performed is notified to the higher-level computer by a response, which causes the higher-level computer to stop resending the command.

[0009]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of a programmable controller system to which an upper link system of a programmable controller according to the present invention is applied. In FIG. 1, reference numeral 1 denotes a host computer, 2 denotes N programmable controllers, and the host computer 1 and the N programmable controllers 2 are connected by a transmission line 3 so that they can communicate with each other.

The host computer 1 is a computer having a general structure such as a personal computer and a mini computer, which executes application programs such as system monitoring such as monitoring of the operating state of the programmable controller and the operating state of each relay. A function request (command) is transmitted to the programmable controller 2 according to the application program, and a response of the processing result is received from the programmable controller 2.

The programmable controller 2 may be a programmable controller having a well-known structure including an upper link unit, receives a command from the upper computer 1, performs processing in response to a command request, and returns a response. It is designed to be sent to.

FIG. 2 shows a communication processing flow of the host computer 1 in the host link system according to the present invention. In this communication processing flow, first, the count value N of the retransmission counter is reset to 0 (step 10), and then a command is transmitted to the programmable controller 2 (step 2).
0).

An example of the data format of this command is shown in FIG. The command data format includes a start delimiter part indicating the beginning of a command, a programmable controller number part of a request destination, a retransmission identification information part, a command part consisting of a code or number corresponding to a request function to the programmable controller, a data part and a command. It is composed of a delimiter part representing the end of the. The retransmission identification information of the retransmission identification information part of this command data format is the retransmission identification information for the same request set by the application of the host computer 1,
In this embodiment, it is given by the count value N of the retransmission counter whose initial value is set to zero.

The host computer 1 sets a timer in synchronization with the command transmission (step 30), and monitors whether a response is received from the programmable controller 2 within a predetermined time after the command transmission (step 40).
When the response is not received within the predetermined time, the count value N of the retransmission counter is incremented by 1 (step 5
0), then the count value N is a predetermined value, for example 4,
Whether or not it is determined is performed (step 60). If the count value N is a predetermined value abnormality, communication abnormality processing is performed (step 70), and if the count value N is less than or equal to the predetermined value, the process returns to step 20 and command transmission is performed again.

When a response is received from the programmable controller 2 within a predetermined time from the command transmission,
It is determined whether or not the processed result code is set in the result part of the data format of the response from the programmable controller 2 (step 8).
0). 1 if the processed result code is not set
This is the time when the response is normally obtained by sending the command twice, and in this case, the processing based on the result data of the received response is performed (step 90), and if the processed result code is set to this, It is the time when multiple command transmissions by the same request command are performed, and in this case, the command transmission by the same request command is stopped (step 100).

FIG. 3 shows a communication processing flow of the programmable controller 2 in the upper link system according to the present invention. This communication processing flow is started by the programmable controller upon receiving a command from the host computer 1, in which the count value of the retransmission counter is first determined based on the retransmission identification information of the retransmission identification information section of the command data format. N is 0,
Whether or not it is determined (step 200).

When the count value N is 0, it means that the command is received for the first time. In this case, the received request command is currently processed as a processed command such as a work memory of the programmable controller 2. It is stored in the storage means (step 210). Next, the request command is processed (step 220) and a response is transmitted to the host computer 1 (step 230).

An example of the data format of this response is shown in FIG. The response data format is made up of a start delimiter section that represents the beginning of the response, a request source programmable controller number section, a retransmission identification information section, a command section, a result section, a result data section, and a delimiter section that indicates the end of the response. .

When the count value N is not 0, it means that the command has been received more than once. In this case, the processed command stored in the storage means, that is, the one which the programmable controller 2 has processed immediately before. It is determined whether or not the request command and the newly received request command are the same (step 240), and the request command processed immediately before by the programmable controller 2 and the newly received request command this time. If the requested command is not the same, the process proceeds to steps 210 and 220 to newly store the requested command as a processed command in the memory of the programmable controller 2 and then process the requested command. However, one request command that the programmable controller 2 processed immediately before,
If the newly received request command is the same as this time, a result code indicating that processing has been completed is set in the result section of the response data format, and the response in which the result code indicating processing has been set is the higher order. It is transmitted to the computer 1.

Thus, the programmable controller 2
Does not process the request command from the application program of the host computer 1 twice in duplicate.

FIG. 6 shows a transition example of communication between the host computer 1 and the programmable controller 2.
In this example, a communication failure occurs in the process of transmitting the response B of the command B, so that the host computer 1 transmits the same command B to the programmable controller 2 after a predetermined time. In this case, since the processed result code is set in the result section of the response B due to the second transmission of the command B, the host computer 1 stops the transmission of the command B, and then It will proceed to the stage for transmitting C.

[0023]

As can be understood from the above description, according to the programmable controller host link system of the present invention, one request command processed immediately before by the programmable controller is stored in the storage means, and the programmable controller is operated by the host computer. It is determined whether or not the command transmission from the host computer to the programmable controller is a resend based on the resend identification information added to the command data format to be sent to the request command stored in the storage means at the time of resending. If the new received command is the same as the new received command, the higher-level computer is notified by the response that it has already been processed, and the high-level computer stops resending the command. It is prevented from being processed twice request command from Tsutomu program. This is to add re-transmission identification information management items to the application program without the need for a complicated communication control procedure program by adding re-transmission identification information that can be set and read by the application program in the host computer. Is easily realized with.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a programmable controller system to which an upper link system of a programmable controller according to the present invention is applied.

FIG. 2 is a flowchart showing an example of a communication processing flow of a host computer in the host link system according to the present invention.

FIG. 3 is a flowchart showing an example of a communication processing flow of the programmable controller 2 in the host link system according to the present invention.

FIG. 4 is an explanatory diagram showing a data format example of a command.

FIG. 5 is an explanatory diagram showing an example of a response data format.

FIG. 6 is a time chart showing a transition example of communication between a host computer and a programmable controller.

[Explanation of symbols]

 1 Host computer 2 Programmable controller 3 Transmission path

Claims (1)

[Claims] 1. In an upper link system of a programmable controller for controlling communication between a programmable controller and a host computer, the programmable controller is provided with a storage means for storing one request command processed immediately before, and the programmable controller is connected to the programmable controller from the host computer. Retransmission identification information is added to the command data format to be transmitted to the host computer, and it is determined whether the command transmission from the host computer to the programmable controller is a resend based on the resend identification information. Request command and new received command are compared, and if they are the same, the result code of the response data format is sent from the programmable controller to the host computer to indicate that processing has been completed. Programmable controller upper link system that notifies the computer, the host computer is characterized by being configured so as to stop the retransmission of the command.