NETWORK INTERFACE BOARD HAVING MEMORY MAPPED MAILBOX REGISTERS INCLUDINGALARM REGISTERS FOR STORING PRIORITIZED ALARM MESSAGES FROM PROGRAMMABLELOGIC CONTROLLERS

摘要

A network interface board provides a communication linkbetween a personal computer and a network bus connecting aplurality of programmable logic controllers. The networkinterface board mounts in an expansion slot of the personalcomputer. The programmable logic controllers control theoperation of various machines. The network interface boardincludes mailbox registers for storing messages from the network,including three different queues of alarm messages which thepersonal computer can access in any order. Theses messages couldbe in the form of program steps, allowing the personal computerto directly program a programmable logic controller over thecommunication network.