Campbell Scientific SM4M/SM16M Storage Modules - Manual (Page 23)

4-1
Section 4. Storage Module Memory:
Details of Data Storage
Detailed knowledge of the way data is stored in the Storage Module is not normally
necessary for day-to-day use. However, if you ever need to work the exact memory
available or try to extract corrupted data it may be helpful to know these details.
4.1 File Marks
File Marks are used to separate data in the Storage Module. A File Mark is
automatically placed in the Storage Module’s memory when the module is
connected to a power source (datalogger or retrieval interface), when the
datalogger compiles a program containing Instruction 96, or under program
control. For example, if the user has retrieved data from one datalogger,
disconnects the Storage Module and then connects it to a second datalogger, a
File Mark is placed in the data when the second datalogger is connected. This
mark follows the data from the first datalogger and precedes the data from the
second.
The Storage Module must be disconnected from power for
10 seconds or more to be certain it places a File Mark in
the Storage Module when reconnected.
A File Mark can be placed in the data by using SMS, the *9 Mode command 3
(not in 21X or CR7) or from a special P96 command in the datalogger
program.
The Storage Module will not store contiguous file marks. If a File Mark is the
last thing stored in memory, a second File Mark will not be stored.
4.2 Pointers
The Storage Module has several internal pointers which are used to keep track
of data for both storage and retrieval operations.
The Display Location Pointer (DLP) is used to display Storage Module data.
Ordinarily, when the Storage Module is connected to a datalogger, the DLP
will be at the beginning of the current file. The DLP can be positioned
anywhere within the data, using the nnnnnnG command (see Appendix B).
Data can then be ‘dumped’ to the user device using one of the appropriate
commands (nnnnC, nnnnD or nnnnF). The dump will begin at the DLP and
continue until it reaches the Storage Reference Pointer (SRP) or until the
next File Mark.
The Storage Reference Pointer (SRP), indicates the next location to be
written to in the Storage Module. It will always be at the end of data in the
Storage Module.
CAUTION