What is the difference between FPGA and PLC ?

1. Introduction to FPGA

FPGA (Field-Programmable Gate Array), namely Field Programmable Gate Array, is the product of further development on the basis of PAL, GAL, CPLD and other programmable devices. It emerged as a semi-custom circuit in the field of application-specific integrated circuits (ASIC), which not only solved the shortcomings of the custom circuit, but also overcome the shortcomings of the limited number of gate circuits of the original programmable device.

FPGA design is not a simple chip research, but mainly uses the FPGA model to design products in other industries. Different from ASIC, FPGA is widely used in the communication industry.

The development of FPGA is very different from the development of traditional PC and microcontroller. FPGA is mainly based on parallel operation and is implemented by hardware description language; compared with the sequential operation of PC or microcontroller (whether it is Von Neumann structure or Harvard structure), there is a big difference, which also makes it difficult to get started with FPGA development.

FPGA development needs to start from the top-level design, module layering, logic implementation, software and hardware debugging and other aspects.

Compared with the traditional mode of chip design, FPGA chips are not simply limited to research and design chips, but can be optimized for products in many fields with the help of specific chip models.

From the perspective of chip devices, the FPGA itself constitutes a typical integrated circuit in a semi-custom circuit, which contains digital management modules, embedded units, output units, and input units.

On this basis, it is necessary to fully focus on the comprehensive chip optimization design of FPGA chips, and add new chip functions by improving the current chip design, thereby simplifying the overall structure of the chip and improving its performance.

2. Introduction to PLC

Programmable Logic Controller (PLC), a digital operation controller with microprocessor for automatic control, can store and execute control instructions in human memory at any time.

The programmable controller is composed of functional units such as CPU, instruction and data memory, input/output interface, power supply, and digital-to-analog conversion. The early programmable logic controllers only had the function of logic control, so they were named programmable logic controllers.

Later, with the continuous development, these computer modules with simple functions at the beginning have various functions including logic control, timing control, analog control, multi-computer communication, etc., and the name has also been changed to Programmable Controller (Programmable Controller), but due to Its abbreviation PC conflicts with the abbreviation of Personal Computer (Personal Computer), and for reasons of habit, people still often use the name Programmable Logic Controller and still use the abbreviation PLC.

Now the programmable logic controller used in industry is equivalent to or close to the host of a compact computer, and its advantages in scalability and reliability make it widely used in various industrial control fields.

Whether in the computer direct control system or the centralized and distributed control system DCS, or the field bus control system FCS, there are always a large number of various types of PLC controllers used. There are many PLC manufacturers, such as Siemens, Schneider, Mitsubishi, Delta, etc. Almost all manufacturers involved in the industrial automation field will provide their PLC products.

3. Differences between FPGA and PLC

A. Differences in programming

PLC programming mostly uses relay control ladder diagrams and command statements, the number of which is much less than that of microcomputer instructions. Except for medium and high-end PLCs, there are only about 16 small PLCs in general.

Because the image of the ladder diagram is simple, it is easy to grasp, easy to use, and can be programmed even without computer expertise. It is a small circuit programming.

FPGA programming, using hardware description language HDL, using ISE, VIVADO and other development tools, has its own set of development processes, the programming is more complex, the development workload is large, and the timing analysis is difficult.

B. Program loading difference

The PLC program is compiled by the computer and loaded into the PLC firmware, which is executed by the PLC firmware.

The program of the FPGA is a bit file generated by its own development tool, downloaded to the external flash of the FPGA through the emulator, and the file is automatically loaded to execute the program function when it is powered on. The inside is a real digital circuit.

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