Beginning of time interval that contains required data.
ToTime
End of time interval that contains required data.
TransID
Transaction identifier that is defined as a parameter of the function PointOldValue.
NextFromTime
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.
Description
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 phases. 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.
Return value
Begin time of the next interval of the reading historical values which is saved into the parameter NextFromTime. See also return codes of the function ReadAllPoints.
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