Opc data Access Automation Specification

2.5.2

 

Events  

The automation interface supports the event notification mechanism that is provided with Visual Basic 5.0. 

The Automation server triggers events in response to Async Refresh, Async Read and Async Write Method calls.  In 

addition, Automation server triggers events when data changes according to the client specification. 

The implementation assumes that the Automation Client is equipped to deal with these events.  

2.6

 

Arrays 

By convention, the OPC Automation interface assumes that arrays are 1 based.  If an array is passed to a function that is 

larger than the Count or NumItems parameter, only  Count or NumItems elements will be used, starting at index 1. 

This only applies to parameters for functions and events within the automation interface.  This does not apply to item 

values, where the data type for the item value is itself an array. 

To avoid errors it is suggested that VB code use “Option Base 1”.