A programmable logic controller system having the capability of controlling up to 64 clusters of peripheral controllers, wherein each cluster has up to seven racks of peripheral controllers, each rack having up to 16 individual peripheral controllers. Excepting for the cluster containing the programmable...http://www.google.de/patents/US5225975?utm_source=gb-gplus-sharePatent US5225975 - Network programmable logic controller system with ladder editor and parallel and synchronous logic and I/O scanning
