1756-L72S 程序容易阅读，便于诊断和维护

Its advantages:
1, the program is easy to read, easy to diagnose and maintain;
2, the program is easy to convert between PLC between different manufacturers.
Siemens STL language is powerful, but difficult to read, writing programs also need to be extremely careful, its powerful may be its register addressing (similar to the address pointer in some computer high-level languages), SCL does not have this function, then spend more program code to achieve the same function, Whether the program is excellent should pay more attention to the structure of the program and improve the standardization of program production efficiency, a good PLC program should not only understand themselves, but let more people understand. SCL language is generally used in Siemens PLC to write standard function block FB, and its programming method is completely different from other programming languages of Siemens, such as ladder diagram Lad and statement table STL. At the same time, in order to achieve international standardization of the program, that is, in order to facilitate the transplantation of program code to PLC systems of different manufacturers. Try not to use a Siemens-only feature block in SCL.
For PLC programming, people who generally do industrial control will, experienced people may not be anything for some small skills, but for beginners, it may take a long time to realize.
1. When writing data conversion, especially when the stepper servo position or speed switch, be sure to give a buffer time, do not write the kind of seamless docking program, if seamless docking, often make mistakes, the position may produce inaccurate. In general, it should be given a scan cycle of more than 0.05s or more than two.
2. Position control command, in each return to the origin or start the moment, is to clear the current position to zero. Otherwise, positional errors and cumulative errors will occur.
3. When the position control is back to the origin, it must be used to return to the origin command, and the data can not be taken.
4. When controlling position, use position control as much as possible, do not go relative command, position for programming, but also easier than relative position control.
5. For position control, use pulse + direction control. Try not to double pulse.
6. Write manual and automatic programs separately. The way to make a block.
7. When it is used to rise or fall along the edge, the contact must be placed behind the output coil, otherwise it will not be scanned or unstable.
8. General induction switch, especially the magnetic induction switch of the cylinder has a induction area, and it must be given a time of more than 0.1s when executed. Otherwise, the machine may not be in place, and the program will proceed to the next step.
9. Precision sensors, especially digital measurements, should not be detected immediately after the mechanical position, and the things detected at this time are basically inaccurate, and it is also necessary to give a buffer time.
10. The more complex the program, the simpler the operation, such a machine field operator is like to use. Others ask for simplicity, I ask for complexity, intelligence.
11. It is not necessary to use advanced instructions, generally just meet the requirements.