Chapter 6
VXIplug&play for the VME-MXI-2
VME-MXI-2 User Manual
6-8
© National Instruments Corporation
Warning:
Do not install a VME-MXI-2 configured for VMEbus System
Controller (the Yes option of this control) into another slot without
first reconfiguring it. Neglecting to do this could result in damage to
the VME-MXI-2, the VMEbus backplane, or both.
This means that you should use either the No option to configure it
not to be the System Controller or the Auto option for automatic
configuration whenever you install the VME-MXI-2 into a slot other
than the first slot.
Bus Timeout
The VMEbus Bus Timeout (BTO) is a watchdog timer for transfers on
the VMEbus Data Transfer bus. After the specified amount of time has
elapsed, the BTO circuitry terminates a VMEbus cycle if no slave has
responded. The VME-MXI-2 must provide the VMEbus BTO for
proper operation because when a MXIbus cycle is involved, the
VMEbus timeout must be disabled and the MXIbus BTO enabled. You
should disable the BTO of any other BTO module residing in the
mainframe. If this is not possible, set it to its maximum setting to give
the MXIbus cycles as much time as possible to complete.
The lowest value in the allowable range is 15
µ
s and the highest is
256 ms. The default value is 125
µ
s.
Arbiter Type
You can use the Arbiter Type feature to configure the VME-MXI-2 as
either a Priority or Round Robin VMEbus arbiter. This control is
applicable only if the VME-MXI-2 you are configuring is a VMEbus
System Controller device. The default value is Priority.
When configured for Priority arbitration, the VME-MXI-2 grants the
bus to the highest pending bus request level. In Round Robin
arbitration mode, the 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.
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