[Circle] concern the development of electronic public micro-channel number, learning together!
Electronic DIY, Arduino, 51 microcontroller, STM32 microcontroller, FPGA ......
electronic encyclopedia, technology development, professional experience, interesting knowledge, technology headlines, disassemble equipment ......
Click on the link, free download 100G + electronic design learning materials!
To find out the similarities and differences between the PLC and SCM, SCM must first define what it feels like, what it feels like PLC. In this regard, we briefly review the development of the computer may help, according to the original definition of computer experts, computer system consists of five parts - the control unit (CU), arithmetic unit (ALU), memory (Memory), an input device (Input), an output device (output) composition.
Early computer (transistor or integrated circuit, excluding tubes) a CU or even an ALU by a plurality of circuit boards, and CU is a separate ALU, with increasing the degree of integration, combined in an ALU and CU to the composition a central processing unit (CPU), then CPU integrated into a monolithic integrated circuit generates MPU or MCU, it appeared as Intel4004,8008, 8080,8085,8086,8088, Z80 MPU and the like. Since then, the development of an MPU produces two branches, to a high-performance, high-speed, large-capacity direction, a typical chip such as: Intel8086,286,386,486,586, P2, P3, P4, the speed from 4.7MHz to the current 3.2GHz. Another branch to the multi-direction, a memory (ROM, PROM, EPROM, EEPROM, FLASH ROM, SRAM, etc.), input / output interfaces (Timer / Counter, PWM, ADC / DAC, UART, IIC, SPI, RTC , PCA, FPGA, etc.) all integrated in an integrated circuit and become SOC (System on a Chip).
According to Yu's see, which is widely used in today's single-chip computer, referred to as SCM. This branch is wide variety, bit width from 8-32, pin number from six to several hundred, the operating frequency from tens of KHz to several hundred MHz, both CISC architecture also RISC, are numerous. Commonly used MCS-51 series, MCS-96 series, PIC series, AVR series, ARM7 / 9 series, TMS320 series, MSP430 series, MOTOROLA many microcontrollers and the like.
At this point, we can divide the development of computer-core processors into three phases: CPU, MPU chip-level and board-level SOC.
PLC-what of it? PLC stands for Programmable Logic Controller (programmable process controller), just introduced into China, once referred to as the PC. Later, IBM-PC is widely available, PC became synonymous with personal computers, it was changed to PLC. There is another PLC means a Power Line Carrier (power line carrier).
PLC is a product, but this product is a bit special, in the absence download control program, it does not have any control function, that is, without the application of PLC is useless. PLC is actually a common control platform designed for use in industrial environments, it must be secondary development in order to complete the final control purposes, therefore, it needs to program editing / debugging software fit.
PLC is a smart products, its core controller uses Shiyao options? The CPU board is certainly not considered, MPU have a good few integrated circuits to Z80 MPU, for example, need Z80MPU, PIO, CTC, SIO, EPROM, SRAM, etc., these integrated circuits mounted on a circuit board, this is an early single-board computer. This solution volume is too large for modern requirements. Thus, PLC controller core SCM is the most appropriate.
It can be concluded:
1. PLC is based on single-chip product, is a single-chip integrated circuit, the two are not comparable.
2. MCU can constitute a wide variety of applications, from micro, small to medium-sized and large can, PLC is a special case of single-chip applications.
3. Different PLC manufacturers have the same working principle, similar functions and indicators, there is a certain interchangeability, quality assurance, programming software standardization moving direction. This is the PLC to obtain broad-based applications. The microcomputer application system is the Eight Immortals, fancy, functions vary, of varying quality, learn, use and maintenance is very difficult.
Finally, from an engineering point of view, to talk about the choice of PLC and SCM systems;
1. For individual projects or the number of repetitions few items in the PLC program is sensible and efficient way, a high success rate, can be * good little hand tail, but the cost is higher.
2. For the large supporting projects, SCM system is low cost, high efficiency advantages, but have considerable R & D and industry experience to make the system stable and sustainable operation. The best way is SCM system embedded PLC functionality, which can greatly simplify the SCM system development time, guaranteed performance, efficiency will be guaranteed.
The difference between PLC and SCM
See friends in the discussion of the difference between PLC and SCM, I have to talk nonsense a few words: PLC in fact, has already done a few monolithic (single chip wide range oh) system.
PLC ladder you can be understood as a compilation of calculators and languages is a programming language, just different range! And common practice by the PLC ladder software to convert your C or assembly language (used by the PLC the CPU decision), and then use the assembler or C compiler system compiled into machine code! PLC is running just a few yards only. ladder only allow users to more easily use it.
The same MCS-51 microcontroller PLC production course also be used, only 8-bit CPU in some applications, such as advanced: a large number of operations (including floating point), the embedded system (now UCOS can be transposed to MCS-51), etc., bloated nothing more. I am in an industrial system is to use MCS-51 microcontroller do, but coupled with DSP only, has been able to meet our requirements (our equipment is slow, and control logic-based, but a lot of point oh, 128 I / O it !!), but also using ladder programming, we put our ladder into recycling C51 C51 KEIL be compiled. you do not notice the PLC will choose different types of CPU you! !
Of course, also be used SCM direct the development of the control system, but the developer requires relatively high (not general level capable of), the development cycle, high cost (for some large decency that you need to do the experiment, the printed circuit board requires a pen considerable cost, you can say that you use the simulator, with experimental board to develop, but I want to tell you, do you just verify the feasibility of hardware and software, does not mean that can be used in industrial control systems, because industry the control system requirements for immunity is very high, stable first, rather than the performance of the first, so your circuit board design must constantly test and improve). when you solve these problems, you will find that you have done one of the PLC of course, if you need someone to be able to easily use also need to use a set of software do not need to tell someone your circuit (you can not tell anyone). Some more than humble opinion, there is something wrong place, please correct me, do not hit me Oh! Do not call me Oh! I just want to talk about it !!!
Many people feel very mysterious PLC, PLC is actually very simple, in addition to its internal CPU speed and other functions not as an ordinary microcontroller. PLC is generally 16-bit or 32-bit CPU, a serial channel communicates with the outside of the belt 1 or 2, a timer internal to, to improve the reliability of a watchdog timer coupled sufficient.
PLC key technology lies in its internal curing can explain a ladder language program and auxiliary communications procedures, efficiency ladder language interpreter determines the performance of the PLC, PLC communication program determines the difficulty of exchanging information with the outside world. For simple applications, usually by way of a separate controller operation without the exchange of information with the outside world, there are only internal curing ladder language to explain procedures. In fact, the design of PLC's main job is to explain the development ladder language program.