Abstract

PLC (Programmable Logic Controller) is a modern and compact device used in industry for automatic control. It is a product of an excellent combination of microprocessing technique, software technology and industrial characteristics. However, the application of PLCs in control and especially in training is still limited, due to their relatively high price and the low compatibility of products from different manufacturers. The project is to design and construct an equivalent PLC using the popular 89C51 microcontroller as the CPU. To this aim we have designed the complete circuit and written the equivalent ladder diagram instruction set. This simulation serves two purposes: (1) to create low-price basic PLCs for training and normal control applications, (2) to set ground for the development of more powerful PLCs for the same purposes.