Communication system enabling programmable logic controllers access to

Abstract

A high speed control system allows for transferring messages between a programmable logic controller and a host computer over an Ethernet communications network. The host computer includes prioritized alarm queues for receiving prioritized alarms from the programmable logic controller. Alarms fall into either a local or a global category, and each category supports three types of alarms: warnings, alerts or faults. The system is responsive to the routing address for transferring the messages between the programmable logic controller and the host computer. The host computer can immediately obtain messages from a programmable logic controller without interruption of the execution of its ladder program. The host computer can also receive unsolicited messages from the programmable logic controller. The programmable logic controller can communicate with tasks within the host computer as though those tasks were other programmable logic controllers.