User`s guide

Programming via GPIB and VXI 4
Agilent VISA User’s Guide 121
Using the Memory Access Resource
For VISA 1.1 and later, the Memory Access (MEMACC)
resource type has been added to VXI and GPIB- VXI.
VXI::MEMACC and GPIB- VXI::MEMACC allow access to all of
the A16, A24, and A32 memory by providing the controller
with access to arbitrary registers or memory addresses on
memory- mapped buses.
The MEMACC resource, like any other resource, starts with
the basic operations and attributes of other VISA resources.
For example, modifying the state of an attribute is done via
the operation viSetAttribute (see VISA Resource Classes in
the VISA Online Help for details).
Memory I/O Services
Memory I/O services include high- level memory I/O services
and low- level memory I/O services.
High-Level Memory I/O Services
High- level memory I/O services allow register- level access to
the interfaces that support direct memory access, such as
the VXIbus, VMEbus, MXIbus, or even VME or VXI memory
through a system controlled by a GPIB- VXI controller. A
resource exists for each interface to which the controller has
access.
You can access memory on the interface bus through
operations such as viIn16 and viOut16. These operations
encapsulate the map/unmap and peek/poke operations found
in the low- level service. There is no need to explicitly map
the memory to a window.
Low-Level Memory I/O Services
Low- level memory I/O services also allow register- level
access to the interfaces that support direct memory access.
Before an application can use the low- level service on the
interface bus, it must map a range of addresses using the
operation viMapAddress.