Because the PLC uses a cyclic scanning working mode, it continuously executes the user program from top to bottom and from left to right in one scanning cycle.
This method determines that:
1. PLC program execution is single-threaded, and the data in the data storage can be predicted (all data in the previous scan cycle is immutable and unique).
2. If the user program has time-consuming tasks, it will increase the PLC scanning cycle and reduce the real-time performance of the PLC.
3. The instructions in the PLC are carefully designed, with short execution time, so that the user will not block the program operation.
Users can only use the instructions provided by the PLC manufacturer. There are basically no third-party instruction libraries, and the instructions are not interchangeable between different brands of PLCs, or even between different series of PLCs from the same brand.
I believe that using unofficial libraries can lead to unpredictable consequences, potentially causing PLC programs to crash. For the sake of stability, it's better to use a closed instruction set for your PLC.
Based on point 3, we aim to build our own programs by applying the instructions specified by the PLC manufacturer within the rules they establish.
Simply put, it means that I can only use what others give me.
Even if someone gives you three axes, I can only use a maximum of three axes. If someone doesn't provide you with memory space, I can't write programs using object-oriented programming.
Perhaps my understanding of PLCs is not deep enough, but I believe that modular programming is a suitable programming method for most PLCs.
The process is further divided into individual modules.
Each module retains only one inlet and one outlet to reduce the coupling between modules.
People should be honest with themselves. When you look back at the programs you wrote before and think they are terrible, you've already made progress.
I personally believe there are three levels of PLC programming:
1. They think all other people's programs are garbage.
2. I feel that all the programs I wrote before were garbage.
3. Develop your own PLC and let others write PLC programs according to your own rules.
Not being complacent or arrogant, but being able to stay grounded and drive the development of an industry—I think that's where the value of an industrial control professional lies.
