Determines the mode of data collection.
'auto' Data is periodically fetched for all data
groups associated with this entry. This is
done at data group specific periodic intervals
(cdcDGPollPeriod).
The data thus collected, is formatted and
stored into the current VFile.
In addition at regular intervals (see
cdcVFileCollectPeriod) a new VFile
is created to store data, and the current
VFile is frozen and transferred.
'manual' Data for all data groups is fetched and
collected into the current VFile only when
cdcVFileCommand is set to 'collectNow'.
This object's value cannot be modified while the entry
is in the 'activated' state.