Different Analysis of PLC Control and SCM Control

 PLC is actually a set of already-made single-chip computer system.

     The ladder diagram of PLC can be understood as a programming language like calculator language such as assembly, but the scope of use is different! Also, it is common practice to convert your ladder diagram into C or assembly language (used by PLC) by PLC software. CPU's decision), and then compiled into machine code using assembler or C compiler system! PLC is only a few yards of code. Ladder diagram is just for users to use it more easily.

       The same MCS-51 microcontroller can also be used for PLC production, of course, only 8-bit CPU in some advanced applications such as: a large number of operations (including floating-point operations), embedded systems (now UCOS can also be transplanted to MCS-51), etc., some powerless However, our company is using an MCS-51 single-chip microcomputer system, but with DSP, we can meet our requirements (we have slower equipment and more logic control, but we have a lot of points.) 128 points I/O!!), but also use ladder programming, we convert our ladder diagram to C51 and then use KEIL's C51 to compile. Didn't you notice that different types of PLCs will use different CPUs? !

       Of course, you can also use a microcontroller to directly develop the control system, but the developers are very demanding (not the average level can be competent), long development cycle, high cost (for some large-scale systems you need to do experiments, printed circuit boards need a The pen cost, you can say that you use the simulator, use the experiment board to develop, but I want to tell you that doing so you just verify the feasibility of the hardware and software does not mean that can be used in industrial control systems, because industry The requirements of the control system to combat interference are very high, stable first, not performance first, so your circuit board design must be constantly experimented and improved). When you solve the above problem, you find that you have done a PLC Of course, if you need someone to use it easily, you still need a set of software, so you don't need to tell someone about your circuit (you can't tell anyone else).

       Many people think PLC is very mysterious, in fact PLC is very simple, its internal CPU besides speed is fast, other functions are inferior to ordinary one-chip computer. Usually the PLC uses a 16-bit or 32-bit CPU, with 1 or 2 serial channels to communicate with the outside world, there is a timer inside, to increase the reliability plus a watchdog timer is enough.

      The key technology of PLC lies in that it solidifies a program and auxiliary communication program that can explain the ladder language. The efficiency of the interpreter program of the ladder language determines the performance of the PLC. The communication program determines the difficulty of exchanging information between the PLC and the outside world. For simple applications, it is usually operated as a stand-alone controller. It is not necessary to exchange information with the outside world. It is only necessary to internally solidify a program that can interpret the ladder language.

      In fact, the main task of designing a PLC is to develop a program that explains the ladder language.

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