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Chapter 6 NI-VXI Configuration Utility
VXI/VME-PCI8022 for Solaris 6-26
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National Instruments Corporation
Transfer Limit
You can use this feature to control how many data transfers the
VXI/VME-MXI-2 will perform on the VXI/VMEbus before releasing
it to another master device that is requesting use of the bus.
The available options you can choose from are 16, 64, and 256 transfers.
If you do not want the VXI/VME-MXI-2 to hold the VXI/VMEbus long
enough to perform 256 transfers (the default value), you can use this
control to select a smaller value.
Arbiter Type
You can use the Arbiter Type feature to configure the
VXI/VME-MXI-2 as either a Priority or Round Robin VMEbus arbiter.
This control is applicable only if the VXI/VME-MXI-2 you are
configuring is a VMEbus System Controller (VXI Slot 0) device. The
default value is Priority.
When configured for Priority arbitration, the VXI/VME-MXI-2 grants
the bus to the highest pending bus request level. In Round Robin
arbitration mode, the VXI/VME-MXI-2 grants the bus to the next
highest bus request level after the level of the previous bus owner. This
effectively gives the same priority to each bus request level. Refer to the
VMEbus specification for more information on the different types of
arbiters.
Request Level
The VXI/VME-MXI-2 uses one of the four VMEbus request levels
(0 to 3) to request use of the VME Data Transfer Bus (DTB). The
VXI/VME-MXI-2 requests use of the DTB whenever an external
MXIbus device, such as a PCI-based computer with a PCI-MXI-2
interface, attempts a transfer that maps into the VXI/VMEbus
mainframe.
The VXI/VME-MXI-2 uses VMEbus request level 3 by default, as
required by the VXIbus specification. This is suitable for most VXIbus
systems. However, you can change the VXI/VME-MXI-2 to use any of
the other three request levels (0, 1, or 2) by changing the setting of the
Request Level control. You may want to change request levels to
change the priority of the VXI/VME-MXI-2 request signal. For more
information, refer to the VMEbus specification.