A new architecture for high-performance programmable logic controller

The authors developed an economical programmable logic controller (PLC) with high efficiency suitable for plant control systems. This PLC compose of several cards with various functions. The main processor card determines the efficiency of a PLC. Therefore a PLC's efficiency can be improved by upgrading the main processor card. Also, the main processor card constitutes nearly all the cost of a PLC. Therefore a PLC's cost could also be reduced by restructuring the main processor card. In a conventional main processor card, operations are entrusted to either microprocessing unit (MPU)-based processing or application specific integrated circuit (ASIC)-based processing. Main processor cards need architectural redesign in order to improve efficiency and to reduce cost simultaneously. The conventional ASIC-based processing is partially replaced by MPU-based processing, and the rest of the processing remains assigned to an ASIC, which serves as a control co-processor. The MPU and the co-processor share the tasks of control language processing and control operation that used to be performed collectively by the conventional ASIC. The new main processor card, consisting of an MPU and a co-processor, has faster processing speed, larger capacity and lower price than the conventional model, because of the functions of the co-processor, the MPU/co-processor configuration and task sharing between them. This new main processor card enabled the authors to develop a PLC that is more efficient and economical.