User`s guide

100 Agilent VISA User’s Guide
4 Programming via GPIB and VXI
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.
• viPeek/viPoke calls do not return status codes.