User manual

Chapter 7 VXIplug&play for the VXI-MXI-2

Arbiter Timeout

An arbitration timeout feature is available on the VXI-MXI-2 when it is

acting as the VMEbus arbiter. This feature applies only to a VXIbus

Slot 0 VXI-MXI-2. The default value is Enabled.

The timer begins when the arbiter circuit on the VXI-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 VXI-MXI-2 is always a Release On Request requester. However,

you can configure whether the VXI-MXI-2 acts as either a fair or unfair

requester on the VXIbus. 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 VXI-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-MXI-2

requests use of the DTB whenever an external MXIbus device attempts

a transfer that maps into the VXIbus mainframe.

The VXI-MXI-2 uses VMEbus request level 3 in its factory-default

setting. This is suitable for most systems. However, you can change the

VXI-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-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

VXI-MXI-2 will perform on the VXIbus 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-MXI-2 to hold the VXIbus long

enough to perform 256 transfers (the default value), you can use this

control to select a smaller value.