User`s guide

Programming via GPIB and VXI 4
Agilent VISA User’s Guide 113
Using VXI-Specific Attributes
VXI-specific attributes can be useful to determine the state of your VXI
system. Attributes are read-only and read/write. Read-only attributes
specify things such as the logical address of the VXI device and
information about where your VXI device is mapped. This section
shows how you might use some of the VXI-specific attributes. See VISA
Resource Classes in the VISA Online Help for information on VISA
attributes.
Using the Map Address as a Pointer
The VI_ATTR_WIN_ACCESS read-only attribute specifies how a
window can be accessed. You can access a mapped window with the
VISA low-level memory functions or with a C pointer if the address is
de-referenced. To determine how to access the window, read the
VI_ATTR_WIN_ACCESS attribute.
VI_ATTR_WIN_ACCESS Settings
The VI_ATTR_WIN_ACCESS read-only attribute can be set to one of
the following:
Table 26 Settings for the VI_ATTR_WIN_ACCESS Attribute
Setting Description
VI_NMAPPED Specifies that the window is not mapped.
VI_USE_OPERS Specifies that the window is mapped and you can only use
the low-level memory functions to access the data.
VI_DEREF_AD
DR
Specifies that the window is mapped and has a
de-referenced address. In this case you can use the
low-level memory functions to access the data, or you can
use a C pointer. Using a de-referenced C pointer will
allow faster access to data.