Basic instruction of PLC and characteristics

PLC programming languages and computer languages, have distinctive features, which is different from a high-level language, and with the General Assembly, it is both easier to write, and to meet the requirement to debug. At present, there is no programming language to the manufacturers of products are compatible. If Mitsubishi products has its own programming language, OMRON products also has its own language. But no matter what type of PLC, its programming language has the following characteristics:

1. the graphical command structure: the program consists of graphic expression, instruction by a different graphic symbols, easy to understand and remember. System software developer has required independent operations in industrial control function into symbolic figure, users combine these graphics to suit your needs, and enter the appropriate parameters. In part of the logical operations, almost all manufacturers use similar to the ladder diagram of relay control circuit, it is easy to accept. Such as Siemens control system flowcharts to express, which use graphical symbols for binary logic elements to express the relation is very intuitive and easy to understand. More complex arithmetic, time counts, and so on, generally refer to the ladder or logic elements, although symbolic logic than computation, the popular

2. clear variable constants: graphic breaks equivalent opcode, providing functions, the operand is filled by the user, such as: K400,T120. PLC variables and constants, and their values defined, determined by the model, available in the product brochure.

3. the simplified procedure structure: PLC programs are usually very simple, typical for block-type structure, different blocks perform different functions, are able to program the entire process control functions and has a clear concept of the control order.

Simplifies software build process using assembly language and high-level programming language, to complete the editing,

1. the process of compiling and linking the three, and used programming languages, only need to edit a process, and the rest done automatically by the system software, the whole editing process is conducted in a conversation, without requiring users to have advanced software design skills.

2. the enhanced debugging methods: either assembler, or advanced language program, have posed a headache for editors, and PLC program debugging provides perfect conditions, use the programmer, programmer and PLC on the keypad, display and editing, debugging, monitoring, and support of the software, diagnostic and debugging operations are very simple.

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