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106 Agilent VISA User’s Guide
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Programming via GPIB and VXI
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 .