What is a hard PLC? The so-called hard PLC from the strict sense is the hardware or a dedicated ASIC chip to achieve PLC command hold. The soft PLC is to use some common CPU or MCU to achieve the interpretation of PLC instructions or compiled hold.
Like Mitsubishi (FX) and Omron PLC are mostly hard PLC, and Siemens has several models are soft PLC.
The core of the hard PLC is a bit processor, that is, a dedicated PLC dedicated PLC chip, the previous manufacturers of this processor is the implementation of their own instructions, but since the great and sacred IEC61131-3 appeared, everyone Are in line with this standard, IEC61131-3 defines five languages ​​- LD, FBD, SFC, ST, IL where IL is the most like the assembly, so most of the manufacturers of this bit processor is the implementation of a class IL language. We are here to name this bit temporarily as an IEC processor. There are manufacturers to use FPGA to achieve this processor, because the processor is the implementation of special instructions, so the speed is relatively soft PLC is much faster times. But it also has its weakness, that is, flexibility is not high, and generally can only handle bit instructions, and modern PLC function more powerful, the analog processing and DCS has been comparable, so manufacturers generally have to add A common CPU to handle the implementation of analog and complex functions.

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