Chapter 5
Functional Overview
5-6
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VXI Bus
VXI Addressing
The VXIpc 870 Series computers feature the MITE and MANTIS custom
ASICs for accessing the VXI backplane resources. To access VXI memory
or VXI devices, the VXIpc 870 Series uses the multiple-windowing
scheme of the MITE, which makes it possible to access all of VXI address
space. You can configure the VXI address windows to view specific areas
of VXI memory, or you can use NI-VXI/VISA to do this automatically.
The MITE exports a total of eight independent VXI address windows. The
NI-VXI/VISA software driver uses three separate windows
—
one for VXI
configuration space (A16), one for memory space (A24, A32), and one
for internal use. The remaining five windows are completely user
configurable. You can use one or all five windows; you can also configure
the size and location of the windows. This multiple-windowing scheme
alleviates the performance penalty related to the context switching of one
window that you would constantly have to move between the different
address spaces.
DMA Transfers to and from VXI
The VXIpc 870 Series can perform block-mode transfers using one of the
two on-chip DMA controllers on the MITE. Controlling external VXI
devices often consumes valuable CPU time because the microprocessor
typically shoulders the burden of transferring data to and from devices.
However, MITE-based VXI controllers, such as the VXIpc 870 Series, free
up CPU processing time by moving the burden of block data transfers to
one of the DMA controllers integrated in the MITE. Instead of the
computer microprocessor transferring the data and/or commands, the
NI-VXI/VISA software uses the MITE ASIC to execute the block data
transfers. While the MITE transfers the data, the processor can perform
application-specific tasks, such as data presentation and analysis.
VXI Slot 0 Functionality
The VXIpc 870 Series computers have full VXI Slot 0 capability, including
a MODID register and a CLK10 source, as required by the VXIbus
specification. You can also install the VXIpc 870 Series in another slot and
use it in Non-Slot 0 mode. No matter what your configuration needs, the
VXIpc 870 Series can automatically detect whether it is inserted into Slot 0
and automatically enable or disable the Slot 0 onboard circuitry without
switches and jumpers.
