Asus PCI-DA2200 User Manual page 241

ASUS GUI RAID Manager: Basic Operations at Startup
Fault Bus is a proprietary enclosure management interface. It
will warn the user if a dangerous situation occurs within the
RAID system. Fault Bus gathers the failure signals from the
cooling fans, redundant power supply, enclosure temperature
sensor and UPS device. In the GUI RAID Manager, it reports
this failure information to the user by displaying a red "X" on
whichever device has failed.
Fault Bus only collects the failure signals; it does not detect the
temperature, fan rotation, power supply failure or the UPS power
failure. Either a user-designed circuit or a 3rd-party circuit is
necessary for Fault Bus. This circuit must be configured properly
for Fault Bus to work. To configure the user-designed/3rd-party
circuit, double-click on the Fault Bus icon with your mouse.
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3.6 Working with Windows