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Material Source: Internet
Editor: strongerHuang
Can microcontrollers replace PLCs? This question is like asking if flour can replace noodles, the answer is no. The first time you hear this answer, many people may have questions, microcontrollers are obviously so powerful and feature-rich, why can’t they replace PLCs?
So today we will understand what microcontrollers and PLCs are, and what the differences between them are.
1. Microcontroller
A microcontroller (Single Chip Microcomputer), also known as a microcontroller unit (MCU), is an integrated circuit chip that uses very large scale integration technology to integrate a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), various I/O ports, interrupt systems, timers/counters, and other functions (which may also include display driver circuits, pulse width modulation circuits, analog multiplexers, A/D converters, etc.) into a single silicon chip, forming a small and complete microcomputer system that is widely used in various fields. Examples include mobile phones, PC peripherals, remote controls, automotive electronics, and control of stepper motors and robotic arms in industrial applications, where the presence of MCUs can be seen.
The history of microcontrollers is not long, but the development has been rapid. Its emergence and development are roughly synchronized with the emergence and development of microprocessors. Since Intel first launched a 4-bit microprocessor in 1971, its development until now can be roughly divided into five stages.
The initial stage of microcontroller development (1971 to 1976): In November 1971, Intel first designed the 4-bit microprocessor Intel 4004 with an integration level of 2000 transistors/chip, and equipped it with RAM, ROM, and shift registers, forming the first MCS-4 microprocessor. Subsequently, the 8-bit microprocessor Intel 8008 was launched, along with other companies’ successive releases of 8-bit microprocessors.
The low-performance microcontroller stage (1976 to 1980): Represented by the MCS-48 series launched by Intel in 1976, which integrated an 8-bit CPU, 8-bit parallel I/O interface, 8-bit timer/counter, RAM, and ROM on a single semiconductor chip. Although its addressing range is limited (not exceeding 4 KB), it does not have serial I/O, and the RAM and ROM capacity is small, the interrupt system is also relatively simple, but its functions can meet the needs of general industrial control and intelligent instruments.
The high-performance microcontroller stage (1980 to 1990): The high-performance 8-bit microcontrollers launched during this stage generally come with serial ports, multi-level interrupt processing systems, and multiple 16-bit timers/counters. The on-chip RAM and ROM capacity increased, and the addressing range could reach 64 KB, with some chips also equipped with A/D conversion interfaces.
The 16-bit microcontroller stage (1983 to 1989): In 1983, Intel launched the high-performance 16-bit microcontroller MCS-96 series, which adopted the latest manufacturing technology, achieving a chip integration level of 120,000 transistors/chip.
The all-round high-level development stage (1990 to present): So far, microcontrollers have also shown a trend of transitioning from traditional 8-bit processor platforms to 32-bit advanced RISC processor platforms, but 8-bit machines are still hard to replace. 8-bit microcontrollers are low-cost, affordable, easy to develop, and their performance can meet most needs. Only in high-tech fields such as aerospace, automotive, and robotics, where high-speed processing of large amounts of data is required, do we need to choose 16/32-bit, while in general industrial fields, 8-bit general-purpose microcontrollers are still the most widely used. Microcontrollers are developing towards higher levels in terms of integration, function, speed, reliability, and application fields.
The characteristics of microcontrollers are that programming and maintenance are relatively complex, the programming languages commonly used are C or assembly language, the cost is low, and the I/O interfaces are relatively limited.
2. PLC
PLC, short for Programmable Logic Controller, is a digital operation electronic system specially designed for application in industrial environments. It uses a programmable memory to store instructions for executing logic operations, sequential control, timing, counting, and arithmetic operations, and controls various types of mechanical equipment or production processes through digital or analog inputs and outputs.
3. Why can’t microcontrollers replace PLCs?
1. Stability and Reliability
Some say this is a pseudo-question, microcontrollers are components, while PLCs are systems composed of components and large software, there is no comparability between the two in this aspect. This is correct; most PLC control chips are actually microcontrollers, which means that PLCs can be seen as secondary development of microcontrollers. In terms of industrial protection levels, the stability and reliability of microcontrollers cannot compare to PLCs, which are IP67 products (IP is a marking letter, the first marking digit indicates the level of protection against contact and foreign objects, the second marking digit indicates the level of water protection). Moreover, PLCs that can cope with harsh industrial environments have also developed a set of redundancy systems. If the comparison of stability and reliability is meaningless, then let’s analyze from other aspects.
2. I/O Functionality
The I/O points of microcontrollers are indeed limited, while PLCs have corresponding I/O points that can directly connect to industrial field devices (such as buttons, switches, current transmitters, motor starters, or control valves) for different field signals, and connect to the CPU motherboard through a bus. Almost any production line in industry has hundreds or even thousands of I/O points, which microcontrollers cannot compare.
3. Expansion Functionality
A complete industrial production line, besides control, also requires communication, upper-level control, configuration, motion control, and display, all of which rely on a complete industrial system and communication protocols, such as Siemens’ PROFIBUS-DP communication, Mitsubishi Heavy Industries’ CC-LINK, etc. The communication between microcontrollers and PCs, or between microcontrollers, mostly uses serial ports. The serial port of microcontrollers is full-duplex asynchronous communication. So can microcontrollers implement communication protocols like MODBUS, PROFIBUS, CAN open, Ethernet, etc.? Perhaps microcontrollers can do it, but that involves the next analysis point, the development cycle.
4. Development Cycle
There are over 200 brands of PLCs, and almost every brand has different programming software, which is constantly being improved to better serve electrical engineers. Various program blocks are becoming increasingly user-friendly, such as PID modules, motion control modules, etc., greatly reducing the development pressure on engineers and shortening the development cycle. How can microcontrollers achieve this? Without ready-made modules, they can only be developed. Engineers who have worked on non-standard automation equipment will encounter a problem—insufficient construction time. PLCs, as highly integrated and modular products, face challenges in meeting the development cycles required for equipment, not to mention microcontrollers that are like a blank sheet of paper.
5. Communication Distance
Most production lines now need to integrate and monitor across regions, using communication methods like Ethernet with repeaters, or directly using civilian broadband optical fibers. The final product may end up using Microsoft’s IE browser. Clearly, PLCs have RJ-45 interfaces, and even if the main body doesn’t have RJ-45, Ethernet modules can be added. Can a PCB board equipped with a microcontroller add this interface and develop Ethernet communication? How long will development take?
6. Programming Language
This point is an advantage for microcontrollers but also a disadvantage. As mentioned above, there are over 200 brands of PLCs, and even more programming software. Although most PLC programming languages are quite similar, engineers need to understand each PLC brand’s hardware parameters, soft components, and programming software from scratch to use them effectively. In contrast, microcontrollers use C or assembly language for programming, which is universal for any microcontroller. In other words, learning C or assembly language allows one to apply any microcontroller to develop desired functions (provided there is a relevant foundation in electrical and electronic engineering). However, electrical engineers are not electronic engineers; their work does not solely consider how microcontrollers drive relays to control machine tools. Some electrical engineers may not even know C or assembly language. In recent years, with the promotion of the IEC-61131-3 standard, more PLCs support multiple programming languages, such as ST language similar to C, and CFC language similar to circuit diagrams. This convenient functionality is something traditional microcontroller development environments cannot achieve.
4. Conclusion
From the above discussion, we can see that PLCs can actually be seen as secondary application development of microcontrollers, but they also have their own distinct characteristics. So far, China’s microcontroller applications and embedded system development have gone through more than twenty years, covering various fields such as national economic construction, military, and household appliances, especially in industries like mobile phones, automotive navigation devices, PDAs, smart toys, smart home appliances, and medical devices. Currently, there are over 100,000 engineers engaged in microcontroller development and application in high-end industries.
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