Catalog

I Essential Differences Between PLC and Microcontrollers

(1) PLCis a mature control system composed of microcontrollers, and is the product of mature and stable microcontroller application system. It has a strong universality.

(2) Microcontrollers can constitute a variety of application systems, and have a wider range of use. As for Microcontrollers, it is only an integrated circuit and can only be applied with other components and software.
(3) From the view of engineering use, it's convenient for the single project or the project with few repetitions to use PLC. Because it has a high success rate, a good reliability. However, the cost is high.

(4) For large scale supporting projects, the adoption of SCM system(Supply Chain Management system) has the advantages of low cost and high efficiency, but it requires considerable research and development strength and industrial experience to make the stytem stable.     

What Is a Supply Chain Management System?    

II Characteristic and Functions of PLC

In essence, PLC is a set of Microcontroller (the range of Microcontroller is wide) system. But PLC also has its characteristic: 

PLC widely uses the ladder diagram to replace the computer language, and has certain advantage to the programming. You can regard the ladder diagram as computer language such as assembly, though they have a different using range. Generally the PLC transform your ladder diagram into C or assembly language(determined by the CPU used by the PLC), and then use the assembly or C to compile into machine code. the PLC only runs machine code. The ladder diagram just makes it easier for the user to use.
As what have said, MCS-51 MCU can also be used for PLC production, but only for 8-bit CPU in some advanced applications, such as a lot of calculation (including floating point operation), embedded systems (now UCOS can also be transplanted to MCS-51), and it;s just a little powerless working, but with DSP can meet the general requirements.In addition, by using trapezoid graph programming, we can convert the trapezoid graph to C51 and compile it with KEIL's C51. We can also find that different types of PLC will choose different CPU, in fact, the PLC is a complete set of single-chip computer system.  

Internal Structure of MCS-51

Of course, you can also use MCU directly to develop control system, but it has quite a high requirement for developers(it's not general level can be competent),like the long development cycle, high cost, and you need to do experiments for some large system.The printed circuit board requires a very high cost, and you could use the emulator or experimental board to replace it, , but it;s just verify the feasibility of hardware and software, and it can't mean that can be used in industrial control system. Because the requirements for industrial control system against interference is very high, and it requires stable first, rather than the first performance, so you have to experiment and improve your circuit board design again and again .When you solve the above problems, you will find that you have made a PLC.

In fact, it is not a mystery to see PLC. PLC is very simple, and the functions of its internal CPU except speed are inferior to the ordinary Microcontroller. Usually, PLC uses 16 or 32 bit CPU, with 1 or 2 serial channels to communicate with the outside world, and a timer can be provided inside. If you want to improve its reliability , you can add a watchdog timer .

PLC Components and Their Functions

In addition, the key technology of PLC lies in the internal solidification of a program that can explain the trapezoidal graph language and the auxiliary communication program. For simple applications, which usually operate as independent controllers, there is no need to exchange information with the outside world, just internal solidification of programs that can interpret the language of the trapezoid diagram.In fact, the main job of designing PLC is to develop program to explain the ladder diagram language. Single chip microcomputer can replace PLC completely now. In the past, due to the weak stability and anti-electromagnetic interference capability compared with PLC, the current single chip has achieved high stability and strong anti-interference capability, which has been replaced in some fields.

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Ordering & Quality

Photo	Mfr. Part #	Company	Description	Package	PDF	Qty
	RL7520WS-R10-F	Company:Susumu	Remark:RES SMD 0.1 OHM 2W 3008 WIDE	Package:Wide 3008 (2075 Metric), 0830	RL7520WS-R10-F  Datasheet	In Stock:19360 Inquiry	Inquiry
	A3P030-1QNG48I	Company:Microsemi	Remark:IC FPGA 34 I/O 48QFN	Package:48-VFQFN Exposed Pad	A3P030-1QNG48I  Datasheet	In Stock:146 Inquiry	Inquiry
	MR27T12800J	Company:OKI	Remark:	Package:TSSOP-48	MR27T12800J  Datasheet	In Stock:710 Inquiry	Inquiry
	P89LPC9361FDH518	Company:NXP	Remark:P89LPC9361FDH518, NXP, Embedded - Microcontrollers	Package:28-TSSOP (0.173", 4.40mm Width)	P89LPC9361FDH518  Datasheet	In Stock:118 Inquiry	Inquiry
	MC68882CFN25A	Company:NXP	Remark:-	Package:PLCC68	MC68882CFN25A  Datasheet	In Stock:115 Inquiry	Inquiry
	MC33742PEG	Company:NXP / Freescale	Remark:IC SYSTEM BASE W/CAN 28SOIC	Package:28-SOIC (0.295", 7.50mm Width)	MC33742PEG  Datasheet	In Stock:28162 Inquiry	Inquiry
	XC4VFX20-11FFG672I	Company:Xilinx Inc.	Remark:IC FPGA 320 I/O 672FCBGA	Package:672-BBGA, FCBGA	XC4VFX20-11FFG672I  Datasheet	In Stock:356 Inquiry	Inquiry
	Z8F042ASB020EG	Company:ZiLOG	Remark:IC MCU 8BIT 4KB FLASH 8SOIC	Package:8-SOIC (0.154", 3.90mm Width)	Z8F042ASB020EG  Datasheet	In Stock:802 Inquiry	Inquiry
	DSPB56374AE	Company:NXP / Freescale	Remark:IC DSP 24BIT 150MHZ 52-LQFP	Package:52-LQFP	DSPB56374AE  Datasheet	In Stock:10211 Inquiry	Inquiry
	MC9S12D32MFVE	Company:Freescale	Remark:MCU 16-bit HCS12 CISC 32KB Flash 2.5V/5V Automotive 80-Pin PQFP Tray	Package:QFP	MC9S12D32MFVE  Datasheet	In Stock:74 Inquiry	Inquiry