Programmable logic controllers (PLCs) are members of the computer family, designed and manufactured for industrial control applications. Early PLCs were called programmable logic controllers (PLCs) and were primarily used to replace relays for logic control. With technological advancements, the functions of these devices have far exceeded the scope of logic control; therefore, today they are called programmable controllers, abbreviated as PCs. However, to avoid confusion with the abbreviation for personal computer, the abbreviation PLC is still used.
I. Main Features of PLC
1. High reliability
2. Abundant I/O interface modules
3. Adopting a modular structure
4. The programming is simple and easy to learn.
5. Simple installation and convenient maintenance
II. Functions of PLC
1. Logic control
2. Timed control
3. Counting control
4. Step (Sequence) Control
5. PID control
6. Data control: PLC has data processing capabilities.
7. Communication and networking
8. Other: PLCs also have many special function modules suitable for various special control requirements, such as positioning control modules and CRT modules.
PLD is short for Programmable Logic Device, and FPGA is short for Field Programmable Gate Array. The two have basically the same function, but their implementation principles are slightly different. Therefore, we can sometimes ignore the difference between the two and refer to them collectively as programmable logic devices or PLD/FPGA.
PLDs are one of the most dynamic and promising technologies in the field of electronic design, and their impact is no less than that of the invention and use of microcontrollers in the 1970s. What can PLDs do? It is no exaggeration to say that PLDs can perform the functions of any digital device, from high-performance CPUs to simple 74 circuits.
A PLD (Power Delivery Logic Controller) is like a blank sheet of paper or a set of building blocks. Engineers can freely design a digital system using traditional schematic input methods or hardware description languages. Software simulation allows us to verify the correctness of the design beforehand. After the PCB is completed, the PLD's online modification capabilities allow for design changes at any time without altering the hardware circuitry. Using PLDs to develop digital circuits can significantly shorten design time, reduce PCB area, and improve system reliability.
A typical PLD consists of an AND gate and an OR gate array. Any combinational logic can be described by an AND-OR expression. Therefore, a PLD can perform a large number of combinational logic functions in the form of product sums. The products at this stage are mainly PAL (Programmable Array Logic) and GAL (General Purpose Array Logic).
