HP 49g Graphing Calculator - Manual (Page 103)

Unlike the HOME directory, port memory cannot be subdivided into
directories. A port can only contain two types of objects:
® backup objects
® library objects.
Accessing port contents
In order to access the contents of the variables stored in the ports you can
use File Manager. For details on how to use File Manager, refer to the
User’s Guide.
Alternatively, you can access the contents of libraries and ports, by
pressing 0(DB).
a
fmiction key menu of the attached libraries and the
available ports is displayed.
® To view the contents of a port, press the function key that corresponds
to the port. The contents are displayed as a function key menu.
® To access the fimctions in an attached library, press the function key
that con'esponds to the library. The functions it contains are displayed
as a function key menu. To nm a function, press the function key that
corresponds to the function.
Backup objects
You generally use backup objects to save data that you want to keep for a
long time. Backup objects are special copies of objects from your HOME
directory. Note the following points regarding backup objects:
* Backup objects can only exist in port memory.
® You cannot modify the contents of a backup object.
® You can store either a single calculator object as a backup object or an
entire directory. You cairnot create a backup object for selected
objects in a directory.
The HP 49G monitors the integrity of backup objects. Wlren you create a
backup object in a port, the HP 49G calculates a CRC value (cyclic
redimdancy check) based on the binary data that the object contains. A
CRC value is a checksum calculated from the data. This value is stored
with the object.
When you restore a backup object, the calculator re-calculates the CRC
value and compares it to the original value. If the CRC values are not the
same, the calculator warns you that the data is corrupt.
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