Beginning of time interval that contains the required data.
End of time interval that contains the required data.
Transaction identifier that is
defined as a parameter of the function PointOldValue.
Using the parameter allows the user to split the reading historical values into several periods (their number is optional).
A nonzero time value of the parameter means that the reading was
finished for the values with the timestamp and older. The system
will generate the next calling the function ReadStoredData where
the value of the parameter FromTime is equal to the value of
the parameter NextFromTime.
Zero value of the parameter NextFromTime means that calling
the function ReadStoredData is finished.
The method allows to divide the reading of historical values, which takes a
long time, into several intervals and to use the time between
individual intervals for reading the current values.
The function ReadStoredData (_ReadStoredData@28 in the Stdcall call convention)
is optional. It is called to get the historical values that are archived in connected
device (if the device allows it). The required values are within an interval defined
by the parameters FromTime and ToTime. As the gaining
historical values from a device could take a long time and block a transmission
of current data (DLL protocol functions are called by one task, i.e.
sequentially), it is possible to split the gaining of the values into several
Writing a new interval into the parameter NextFromTime will cause
the generating of the next calling the function ReadStoredData with defined parameter FromTime.
The sequence of callings is finished by writing 0.0 into the parameter NextFromTime.
Ignoring the function is performed by writing 0.0 into the parameter NextFromTime and
the function return code RQ_IGNORED. The values, gained by this calling, must be sent
by using the call-back function PointOldValue.
Begin time of the next interval of the reading historical values
which is saved into the parameter NextFromTime. See also return codes of the