User manual

Chapter 7 VXIplug&play for the VXI-MXI-2
VXI-MXI-2 User Manual 7-8 © National Instruments Corporation
Warning: Do not install a VXI-MXI-2 configured for VMEbus System Controller
(VXI Slot 0) into another slot without first reconfiguring it to either
Non-Slot 0 or automatic configuration. Neglecting to do this could
result in damage to the VXI-MXI-2, the VXIbus 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 VXI-MXI-2 into a slot other
than Slot 0. You also have the option of changing the hardware jumper
setting.
Bus Timeout
The VXIbus 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 VXI-MXI-2 must provide the VXIbus BTO for proper
operation because when a MXIbus cycle is involved, the VXIbus
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 µs and the highest is
256 ms. The default value is 125 µs.
Arbiter Type
You can use the Arbiter Type feature to configure the VXI-MXI-2 as
either a Priority or Round Robin VMEbus arbiter. This control is
applicable only if the VXI-MXI-2 you are configuring is a VXIbus
Slot 0 device. The default value is Priority.
When configured for Priority arbitration, the VXI-MXI-2 grants the
bus to the highest pending bus request level. In Round Robin
arbitration mode, the VXI-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.