Chapter 6
VXIplug&play for the VME-MXI-2
© National Instruments Corporation
6-9
VME-MXI-2 User Manual
Arbiter Timeout
An arbitration timeout feature is available on the VME-MXI-2 when it
is acting as the VMEbus arbiter. This feature applies only to a VMEbus
System Controller VME-MXI-2. The default value is Enabled.
The timer begins when the arbiter circuit on the VME-MXI-2 drives
one of the BGOUT lines on the backplane. If no device takes over the
bus within the timeout limit, the BGOUT is removed and the bus is
either idle or granted to another requester.
Fair Requester
The VME-MXI-2 is always a Release On Request requester. However,
you can configure whether the VME-MXI-2 acts as either a fair or
unfair requester on the VMEbus. The default value for this control is
Enabled, signifying a fair requester. For more information on the
different types of requesters, refer to the VMEbus specification.
Request Level
The 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 VME-MXI-2
requests use of the DTB whenever an external MXIbus device attempts
a transfer that maps into the VMEbus mainframe.
The VME-MXI-2 uses VMEbus request level 3 in its factory-default
setting. This is suitable for most systems. However, you can change the
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 VME-MXI-2 request
signal. For more information, refer to the VMEbus specification.
Transfer Limit
You can use this feature to control how many data transfers the
VME-MXI-2 will perform on the 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 VME-MXI-2 to hold the VMEbus long
enough to perform 256 transfers (the default value), you can use this
control to select a smaller value.
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