User manual

Chapter 7 VXIplug&play for the VXI-MXI-2
VXI-MXI-2 User Manual 7-12 © National Instruments Corporation
Auto Retry
The VXI-MXI-2 has an automatic retry feature for cycles that map
from the MXIbus to the VXIbus. This feature works in the same
manner as the Auto Retry control described previously under the VXI
Bus Settings section. You can select Enabled or Disabled for this
control. By default, this option is disabled.
Normally, when a cycle maps from the MXIbus to the VXIbus, any
retry response received on the VXIbus is passed to the MXIbus. If you
enable the Auto Retry feature, the VXI-MXI-2 automatically retries
any VXI cycle that receives a retry response instead of passing a retry
response on to the MXIbus. The VXI-MXI-2 automatically continues
to retry the VXI cycle until it receives either a DTACK or BERR
response, which it then passes to the MXIbus.
Notice that the VXI-MXI-2 has a limit on the number of automatic
retries it will perform on any one cycle. If the limit is exceeded and the
VXI-MXI-2 receives another retry, it will pass a retry back to the
MXIbus even though Auto Retry is enabled.
Parity Checking
You can use the Parity Checking control if you want to disable
MXIbus parity checking. By default, MXIbus parity checking is set to
Enabled, and should not be disabled under normal circumstances.
MXIbus parity is always generated regardless if checking is enabled or
disabled.
Fair Requester
You can use the Fair Requester control to configure the VXI-MXI-2
as either a fair or unfair requester on the MXIbus. The default setting is
Enabled (fair requester), which causes the VXI-MXI-2 to request the
MXIbus only when there are no requests pending from other masters.
This prevents other MXIbus masters from being starved of bandwidth.
The VXI-MXI-2 will request the bus at any time when this setting is
disabled (unfair requester).