User`s guide

Programming via GPIB and VXI 4
Agilent VISA User’s Guide 115
Using Low/High-Level Memory I/O Methods
VISA supports three different memory I/O methods for
accessing memory on the VXI backplane, as shown. All three
of these access methods can be used to read and write VXI
memory in the A16, A24, and A32 address spaces. The best
method to use depends on the VISA program characteristics.
• Low- level viPeek/viPoke
• viMapAddress
• viUnmapAddress
• viPeek8, viPeek16, viPeek32
• viPoke8, viPoke16, viPoke32
• High- level viIn/viOut
• viIn8, viIn16, viIn32
• viOut8, viOut16, viOut32
• High- level viMoveIn/viMoveOut
• viMoveIn8, viMoveIn16, viMoveIn32
• viMoveOut8, viMoveOut16, viMoveOut32
Using Low-Level viPeek/viPoke
Low- level viPeek/viPoke is the most efficient in programs
that require repeated access to different addresses in the
same memory space.
The advantages of low- level viPeek/viPoke are:
• Individual viPeek/viPoke calls are faster than viIn/viOut
or viMoveIn/viMoveOut calls.
• Memory pointers may be directly de- referenced in some
cases for the lowest possible overhead.
The disadvantages of low- level viPeek/viPoke are:
• A viMapAddress call is required to set up mapping before
viPeek/viPoke can be used.