Whats the purpose of the sqlParameter.SourceVersion?

Question

Hi,
In implementing concurrencies i have seen the use of :

 

SqlParameter parm = da.UpdateCommand.Parameters.Add("@PLastUpdatedTime", 
SqlDbType.DateTime, -1, "updatedTime");
parm.SourceVersion = DataRowVersion.Original;
 

It says that it will assign the Orignal TimeStamp value of the "updatedTime" Column in the dataset to "@PLastUpdatedTime".  But it doesnt show the assignment of the value in that column and when i test it for value in that parm parameter, it says NULL. SO what happense here......?
. i'm suppose to pass the value in the "@PLastUpdatedTime" as a search value to find the row and later compares the value in @PLastUpdatedTime with the value in the actual DB table to figure concurrency violoation. How do i fix my problem?
 
TY