METHOD FOR COLLECTING DATA BY A MANUFACTURING PROCESS MANAGER FROM A PLURALITY OF PROGRAMMABLE LOGIC CONTROLLERS

摘要

A data collection method is provided for use on a computer system including a host processor which is coupled to a plurality of programmable logic controllers (PLCs) via a communications bus. Each PLC is coupled to a respective controlled machine to gather Boolean alarm point information from several alarm points associated with that machine. The alarm point information from all the controlled machines is stored in a random access memories (RAM) in a respective PLC. The alarm points are grouped in memory such that a predetermined number of alarm points are stored in a trigger point register in the RAM. The host scans the trigger point registers of all the PLCs to determine if the value of any trigger point has changed since the last time such trigger point was scanned. If such a change of value in a particular trigger point is found, then the host requests that the value of each alarm point within that particular trigger point be transmitted to the host. An appropriate alarm is.then annunciated to the user. However, if the host finds no change in the value of a particular trigger point from the value of that trigger point during a prior scan, then the host does not request the values of the individual alarm points associated with that trigger point.