外文翻譯--可編程控制器-其他專業(yè)(完整版)
【正文】 ween a program and the physical I/O of the PLC. A program generally consists of an interconnection of function blocks, each of which may be written in any of the IEC languages. A function block or program is also called a program anization unit. In addition to the function blocks, the program contains declarations of physical inputs/outputs and any variables local to the program. A program can read and write to I/O channels, global variables, and municate with other programs. Provide the means to transfer information between con?gurations. Tasks control the execution of the program or parts of a program. A task controls one or more programs and/or function blocks to execute. The execution of a program implies that all of the function blocks in the program are processed once. The execution of a function block implies that all of the software elements of the function block are processed once. There are no implied mechanisms for program execution. In order for a program to be executed, it must be assigned to a task, and the task must be con?gured to execute continuously, periodically, or with a trigger. Variables are declared within the different software elements of the model. A local variable is defined at the software element and can only be accessed by the software element. Local variables can be defined for the function block, program, resource, or con?guration. A global variable defined for a con?guration, resource, or program is accessible to all elements contained in it. For example, a global con?guration variable is accessible to all
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