Recent developments and future trends in PLC programming languages and programming tools for real-time control

The programmable logic controller (PLC) is changing to reflect the demands of sequencing and continuous processing applications. The PLC can be thought of as a hardened computer with high speed I/O and communications ports with bus interfacing for multiprocessor or coprocessor enhancements, and a BIOS that supports those features. PLC manufacturers now retain control over both aspects of the PLC which interoperate in a proprietary manner. Via the delineation of the two may come a standard real time operating system or real time kernel which would give rise to true applications portability. Specific topics addressed include relay ladder logic, a structured approach to error dynamic diagnostic information (EDDI), state control language, and process control function blocks. >