What are the characteristics of Hollysys PLC - PLC program?

1. Correctness (low debugging cost)

First of all, the PLC program must be able to work correctly to meet the requirements of the actual control process. This is the essence of the PLC program, and if you don't do that, nothing else makes sense.

2. Reliability (low maintenance cost)

Not only to be right, but also to be reliable. You can't have problems every now and then in three days.

Reliability reflects the long-term stability of the PLC program, which is also the basic requirement for the PLC program. Some PLC programs can work correctly under normal working conditions or legal operation, but after abnormal working conditions (such as temporary power failure, and power on soon) or illegal operation (such as some buttons are pressed out of order, or several buttons are pressed at the same time or pressed many times in a row), the program can not work normally. This kind of program is not very reliable, or unstable, and it is a bad program. A good PLC program can identify the occurrence of abnormal working conditions, and can connect it with normal conditions, so that the program can adapt to a variety of situations, and a good PLC program can refuse illegal operations without leaving "traces". Only legal operations, i.e., preventative robust programming, are accepted. Interlocking is a common means of rejecting illegal operation, and this method is commonly used in relay circuits, and PLCs and system integrators can also inherit this method.

3. Readability (low learning cost)

The designed program is required to be readable, easy to understand, easy to debug, easy for others to read and use your program, and easy to maintain; If necessary, the program can also be used as a standard template for easy promotion.

To make the program readable:

1) The design context of the program should be as clear as possible, and the structure should be hierarchical;

2) Modularization of the functional layer, or design using an object-oriented approach;

3) Use some standard designs and universal designs;

4) The variable layer should be programmed with symbolic names as much as possible;

5) Parameters are set immediately before they are used (set and use);

6) I/O address allocation should be regular, easy to remember and understand;

7) The use of internal devices should also be regular, and the address allocation of the same function should maintain a certain discontinuous "fault margin" (for example, the address allocation of the X function is used to K, then the address allocation of the next function should not start from K+1, but from K+N) to prevent function changes;

8) If necessary, do some annotation work; Readability is something to keep in mind at the beginning of programming. It's not easy to do. Because in the process of program debugging, the increase or decrease of instructions and the change of the use of internal devices may make the original clearer program become a little chaotic. Therefore, there is a certain leeway for debugging to increase or decrease during the design, and then tidy up after the debugging is completed, so that the designed program has higher quality.

4. Briefness (low storage cost)

Making the PLC program as short as possible is also a goal to be pursued.

Short procedures save user storage; In many cases, it is also possible to save time during execution, improve the response speed to input, and improve the readability of the program. Whether the program is short or not can generally be measured by the number of instructions used in the program, and the number of instructions used is small, and the program is naturally short. In general, it is necessary to pay attention to the program structure, extract the commonality of the code segments that implement the same function, and use subroutines, interrupts and other methods to reduce the amount of code; Use process control instructions to simplify procedures, reduce the workload at a certain point in time, do not do what is not needed, and do less if you can do as little as possible; In a small aspect, it is also necessary to replace the weak instructions with a single processing capacity with strong instructions with multi-processing capabilities (use large-level data to replace small-level data or data structures, such as instructions that replace bit-operands with bytes, words, and double-word operands, fault words, status words, control words, communication words, etc.); The same operation that uses indirect addressing instead of a continuous address storage unit; Use block transfer instructions instead of multiple byte, word, and double word transfer instructions, which can be summarized as "batch" operations) and pay attention to the order of instructions, etc., taking into account the readability of the program.

5. Time-saving (low operating cost)

Keeping a program short may save you time in running a program, but being short is not exactly the same thing as saving time.

Because the time to run the program is related to the number of instructions the program has, it is also related to what instructions are used, that is, it is related to the program algorithm. The execution time is different for different PLC algorithms. In addition, there are instructions that are executed at a different time when the logical condition ON is executed at a different time than when the command is off. In addition, due to the use of process control instructions, not all instructions are executed in the program, etc. Therefore, the calculation of the time to run the program is more complicated. However, it is necessary to require that the average time is small and the maximum time is not too long. This can improve the response speed of Beijing Tiantuo Sifang Technology Co., Ltd., which is the core distributor (first-level agent) and system integrator of Siemens Industrial Automation and Drive Group. The key to saving time is to use process control instructions well. Determine some instructions that must be executed according to the situation, as the necessary part, and the rest can be carried out according to the procedure, selectively executed, or designed for some time-sharing work, so as to avoid the maximum time being too long, etc.

6. Easy to modify (low variable cost)

To make the program easy to modify, that is, to be easy to modify.

One of the characteristics of PLCs is that they are convenient and can be flexibly adapted to various situations. The way to do this is by modifying or redesigning the program. Redesigning programs is used to change the situation of PLC process requirements, not only to reprogram but also to reallocate I/O. In most cases, you don't need to reprogram the program, just make some changes. This requires that the program be easily modifiable and easy to modify. Easy to change is flexible, which requires only a few changes to be made to achieve the purpose of changing parameters or changing actions. 1) The method of indirect assignment should be used for parameter setting as much as possible, and the symbol name should be used for constant parameter values as much as possible, so that the name can be known; 2) The control uses intermediate memory (such as M, W) as the medium and the middle layer as much as possible to isolate the direct coupling of I/O in logic and facilitate the change of logic; 3) Try to realize the function plug-in module block, so that users can "freely configure" to achieve on-demand addition, addition and use. In the process of designing PLC programs, the above requirements should be taken into account and balanced at the same time, and the gains outweigh the losses.

What are the characteristics of Hollysys PLC - PLC program?

What are the characteristics of Hollysys PLC - PLC program?

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