Opc data Access Automation Specification

2.4

 

Data Synchronization 

There is a requirement that the VB client be able to read or receive data such that the value, quality, and timestamp 

information are kept in sync. Basically the client needs to be assured that the quality of the data and the timestamp 

matches the value. 

If a client obtains values using any of the Read methods it can be assured that Value, Timestamp, and Quality properties 

will be in synch with each other. 

If a client obtains data by registering for DataChange events, then the Value, Timestamp, and Quality will be in sync 

within the scope of the EventHandler routine. 

If a client mixes these two approaches it will be impossible for the client to ensure that the item properties are exactly in 

sync since an event which changed the properties could occur between the time the client accesses the various properties.