If there is still time remaining before the System Scan time expires, then outstations that still have secondary data available can be re-visited for a period limited by the Maximum Secondary Scan per O/S interval as many times as necessary until the System Scan time expires.
Example:
A driver scans four outstations that are using the same direct channel to communicate with the server.
It first scans the outstations on the channel for current data (the Primary Phase of the scan).
The driver then scans the outstations for time stamped logged data (the Secondary Phase of the scan).
The outstation with Address 5 has a lot of logged data. Some of the data cannot be retrieved within the Maximum Secondary Scan per O/S time. When the Maximum Secondary Scan per O/S time elapses, the driver scans the next outstation for secondary data.
The outstation with Address 6 only has a little logged data to report. Once this data has been retrieved, there is still some System Scan time remaining.
Therefore, the driver re-visits Outstation Address 5 and retrieves the logged data that it did not have time to retrieve on the first visit.
