JP2003091301A - Error prevention method for programmable controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in programming to which a check function for arithmetic error and an overflow error is added, that user's load is large and the program is complicated. SOLUTION: A contact instruction based on a ladder chart is taken (S1), and it is checked whether there is an instruction having the fear of causing an error in executing the instruction in a rung or not (S2). If there is an instruction having the fear of causing an error, an instruction for setting an error flag in the rung to 0 is automatically inserted at the beginning of the rung (S3), and a function of determining whether the instruction is executed or not according to the determination of 0/1 of the rung error flag is automatically added to a write instruction of the rung in which the rung error flag instruction is inserted (S4) and expanded to a program instruction (S5). A programmable controller sets the error flag to 0 to execute each instruction when a rung error flag instruction is given, and stops execution of instruction when an error flag is set to '1' in executing the write instruction to thereby prevent wrong output.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a controller, and more particularly to an error prevention method in programming in a ladder language. [0002] Programmable controller (PC)
As shown in the block diagram in FIG. 4, the basic configuration of the device comprises a program memory unit 1, a control / calculation unit 2, an input unit 3 and an output unit 4. In this configuration, a programmable controller generally uses a stored program method, and transfers a program created by a loader 5 to a program memory unit 1 (including a memory of data and flags). The control / arithmetic unit 2 sequentially reads out the instruction group stored in the memory unit 1, performs an arithmetic operation according to the input condition from the input unit 3 based on the program, and outputs the arithmetic result from the output unit 4 as a control output. I do. [0004] Ladder languages capable of describing the above programs include four arithmetic operations instructions and conversion instructions (square root, BC).
D conversion, BIN conversion, etc.) are prepared, and the user performs programming by combining those instructions. [0005] As the data format of the program, there are usually bit data and word data (single precision type, double precision type, floating point type). When using word data, the single precision type is -32768 to +32768, and the double precision type is -214748648 to +21474836.
48, -3.4 × 10 ³⁸ to + 3.4 × 1 for floating point type
Although 0 ³⁸ can be handled as data, if it exceeds this range during calculation, an overflow will occur and a correct calculation result will not be obtained. In the conversion command, taking BCD conversion as an example, in the case of single precision, the data before conversion is 270F H (9
If it exceeds 999), an error occurs because the BCD cannot be represented by four digits, and a correct result cannot be obtained. [0007] The user must understand these points and incorporate a program so as not to output an incorrect operation result. As a countermeasure for preventing erroneous output, a method of incorporating an error flag and an overflow flag into an instruction as an execution condition, and executing the instruction if it is normal is generally used. FIG. 5 shows an example of this program. In the drawing, a not error flag contact is inserted in the contact sequence, so that the write command (WT) can be executed only when the error flag = 0. As described above, when a user performs programming without considering an overflow error and an operation error in programming, there is a risk that an incorrect result is output as it is. There is. As a countermeasure, there is a method of incorporating an error flag or an overflow flag into an instruction. The overflow flag is rewritten each time an arithmetic operation instruction is executed. Absent. Also, since the error flag, once set, is retained until the task is completed, a program using the knot error flag is effective.
If the error flag is raised even once in the same task, all rungs using the knot error flag contacts are not output, which affects the entire task. In order to reset the error flag to 0,
Although there is an instruction called an error flag coil, it is difficult to use the sequence because it is difficult to see in the sequence and the number of steps is large. An object of the present invention is to provide an error prevention method which solves the above problems. SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to the possibility that when a contact command based on a ladder diagram is input, an error may occur during execution of the command in the rung. When there is a certain instruction, an instruction for setting the error flag within the rung to 0 is automatically inserted at the head of the rung, and the write instruction of the rung into which the error flag instruction within the rung is inserted includes 0/1 of the error flag within the rung. The function of automatically determining whether or not to execute an instruction is automatically added according to the above determination, and is characterized by the following configuration. The program created by inputting each contact command for each rung according to the ladder diagram is transferred to the program memory section of the programmable controller, and the control / operation section of the programmable controller checks for an operation error and an overflow error. In an error prevention method of a programmable controller having a function and executing the program, when each contact command of each rung is input, there is an instruction that may cause an overflow or an operation error in execution of an instruction in the rung. Means for automatically inserting an instruction for setting the error flag within the rung to 0 at the beginning of the rung, and determining whether the error flag within the rung is 0/1 in the write instruction of the rung into which the error flag within the rung is inserted. To automatically add a function to determine whether instructions can be executed The control / arithmetic unit of the programmable controller executes each instruction with the arithmetic error flag and the overflow error flag set to 0 when the in-rung error flag instruction is present, and executes an error flag when executing the write instruction. Is set to 1, the erroneous output is prevented by stopping instruction execution. FIG. 1 shows a program creation processing procedure according to an embodiment of the present invention, in which a loader develops a ladder diagram into program instructions. From the ladder diagram created based on the specification, the user performs each contact logic, which is a component of each rung, by key input operation or the like, and sequentially captures each contact logic for each rung (S1). For example, the input of the rung of the contact configuration shown in FIG. When the fetch of the rung N is completed, it is checked whether or not there is an instruction which may cause an overflow or an operation error in the execution of the instruction in the rung N (S2). This check is performed, for example, when an overflow error in the four arithmetic operations when using single-precision type data or B
It is realized by describing, as a processing program, an error determination method conventionally assumed by a user in programming, such as occurrence of an operation error in CD conversion. If there is no instruction that may cause an error, each of the connected instructions of the rung N is directly expanded into a program instruction (S5). If an instruction which may cause an error is included, an instruction for setting the error flag within the rung to 0 is automatically inserted at the head of the rung N (S3). Further, a function for automatically determining whether or not to execute the instruction by determining whether the error flag in the rung is 0/1 is automatically added to the write instruction (WT) of the rung N in which the error flag instruction in the rung is inserted (S4). ). A function for deciding whether or not to execute these error flag instructions in the rung and whether or not to execute the instructions is added, and these instructions are expanded into program instructions (S5). FIG. 3 shows an example of this development. When the above processing is completed for all rungs (S6), the developed program instructions are loaded into the program memory unit (S7). The program thus input is
The data is transferred from the loader to the program memory unit 1, and is operated and controlled by the control and operation unit 2. The control / arithmetic unit 2 sets the arithmetic error flag and the overflow error flag to 0 when a certain rung N is read and there is an in-rung error flag instruction at the beginning in the execution of the arithmetic / control. Execute the instruction. If an arithmetic error or overflow error occurs during execution of the four arithmetic instructions or conversion instructions, this error flag is set to 1. Then, when the write instruction is executed, it is determined whether or not the error flag is 1, and if it is 1, the instruction execution is stopped. Therefore, when programming in the ladder language, if the user inputs each contact command as it is in accordance with the ladder diagram, programming can be performed in which erroneous output due to occurrence of an error is prevented. For example, even if the rung input shown in FIG. 2 may cause an overflow error,
Even if the user does not input the knot error flag as shown in (1), the loader side can automatically insert the error flag in the rung and insert the error flag determination function as needed. The error flag instruction within the rung automatically inserts only the rung in which an operation error or an overflow error may occur in the instruction within the rung, thereby minimizing the number of insertions of the error flag within the rung for all rungs. In this case, it is possible to reduce a decrease in the calculation speed of the control / calculation unit. As described above, according to the present invention, when there is an instruction that may cause an error, an instruction for setting the error flag in the rung to 0 is automatically inserted at the head of the rung. The function of automatically determining whether or not to execute the instruction by determining whether the error flag in the rung is 0/1 is automatically added to the write instruction of the rung in which the error flag instruction in the rung is inserted. There is. (1) The user is prompted for an overflow error,
Programming that prevents erroneous output can be performed without being aware of operation errors. (2) The user does not need to input a conventional knot error flag command for programming, and the program can be easily viewed. (3) Since an error is detected in units of rungs, the error detection processing is performed only on the rung in which an error may occur, and the number of instructions for erroneous error output is smaller than in the conventional method. Therefore, there is little influence on the processing speed of control and calculation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a program creation processing procedure showing an embodiment of the present invention. FIG. 2 is an example of a ladder diagram in the embodiment. FIG. 3 is a development view of a program memory in the embodiment. FIG. 4 is a block diagram of a programmable controller. FIG. 5 is an example of a ladder diagram in which a conventional knot error flag is inserted. [Description of Signs] 1 ... Program memory unit 2 ... Control / arithmetic unit 3 ... Input unit 4 ... Output unit 5 ... Loader

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Claims (1)

Claims 1. A program created by inputting each contact command for each rung according to a ladder diagram is transferred to a program memory section of a programmable controller, and a control / calculation section of the programmable controller is transferred. In the error prevention method of a programmable controller that executes the program with a check function of an operation error and an overflow error, at the time of inputting each contact instruction of each rung, an overflow or an arithmetic error occurs during execution of an instruction in the rung. Means for automatically inserting an instruction to set the error flag within the rung to 0 at the beginning of the rung when there is an instruction that may occur; Function to determine whether or not to execute an instruction by judging 0/1 of the error flag Means for automatically adding a. If the in-rung error flag instruction is present, the control / arithmetic unit of the programmable controller executes each instruction with the arithmetic error flag and overflow error flag set to 0, An error prevention method for a programmable controller, wherein when a write instruction is executed, if an error flag is 1, instruction execution is stopped to prevent erroneous output.