The difference between PLC and single-chip microcomputer:
1. PLC is a relatively sophisticated control system composed of single-chip microcomputer, and it is a product of the sophisticated and stable single-chip microcomputer application system that has been debugged. There is strong versatility.
2. The single-chip microcomputer can constitute a variety of application systems and have a wider application scale. As far as the "single-chip microcomputer" is concerned, it is only an integrated circuit, and it is necessary to form a system with other components and software to be applied.
3. From the perspective of the application of the project, for a single project or a project with a very small number of repetitions, it is convenient to choose PLC, with high success rate and good reliability, but the cost is high.
4. Regarding the large number of supporting projects, the selection of single-chip microcomputer system has the advantages of low cost and high efficiency, but this requires appropriate development strength and professional experience to make the system stable.
In essence, PLC is actually a set of single-chip microcomputers (single-chip microcomputers with a wide scale) system that have been completed.
However, PLC also has its own characteristics: PLC widely uses ladder diagrams instead of computer language, which has a definite advantage over programming. You can think of a ladder as a programming language just like a calculator language like assembly, but at a different scale! And the general practice is to convert your ladder diagram into C or assembly language (determined by the CPU used by the PLC), and then use the assembly or C compilation system to compile it into machine code! The PLC only runs the machine code. The ladder diagram just makes it easier for the user to use.
As said, then MCS-51 microcontroller can of course also be used for PLC production, only 8-bit CPU in some high-end applications such as: a lot of operations (including floating-point arithmetic), embedded system (now UCOS can also be ported to MCS-51), etc., some can not do anything, but with the addition of DSP can now meet the general requirements, and the same use of ladder programming, the ladder can be converted to C51 and then use KEIL's C51 for compilation. It can also be found that different types of PLC will choose different CPUs, which actually shows that PLC is a set of single-chip microcomputer systems that have been made.
In this case, of course, you can also use a single-chip microcomputer to directly develop the control system, but the requirements for developers are appropriately high (not the general level can be competent), the development cycle is long, and the cost is high (for some large-scale systems, you need to do experiments, printed circuit boards require an appropriate cost, you can say that you use emulators, use breadboards to develop, but I want to inform you, you only verify the feasibility of hardware and software, and do not mean that you can be used in the industrial control system, Because the requirements of the industrial control system to resist disturbance are very high, stable and stable, not functional, so your circuit board planning needs to be constantly tested and improved). When you deal with the above problems, you will find that you have now made a PLC, of course, if you need others to use it simply, you also need a set of operating software, so that you can tell others about your circuit without need. It's also impossible for you to tell anyone.
In this way, PLC is actually not mysterious, many PLCs are very simple, and their internal CPUs are not as good as ordinary single-chip microcomputers in addition to their speed. Generally, PLC uses 16-bit or 32-bit CPU, with 1 or 2 serial channels to communicate with the outside world, and there is a timer inside.
In addition, the key technology of PLC lies in its internal solidification of a program that can interpret ladder language and auxiliary communication program, the efficiency of ladder language explanation program determines the function of PLC, and the communication program determines the difficulty of PLC and the outside world to exchange information. For simple applications, it generally operates as a stand-alone controller, without exchanging information with the outside world, and only requires a program that can interpret the ladder diagram language. In fact, the first task of planning a PLC is to develop a program that interprets the ladder diagram. Today's single-chip microcomputer can completely replace PLC. The former single-chip microcomputer can be compared weakly because of stability and anti-electromagnetic interference, and there is no way to compare with PLC, and now the single-chip microcomputer has achieved high stability and strong anti-interference in some fields, and has been replaced.
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