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VX4101A MultiPaq Instrument User Manual
Glossary–1
Glossary
The terms in this glossary are defined as used in the VXIbus System. Although
some of these terms may have different meanings in other systems, it is
important to use these definitions in VXIbus applications. Terms which apply
only to a particular instrument module are noted. Not all terms appear in every
manual.
Accessed Indicator
An amber LED indicator that lights when the module identity is selected by
the Resource Manager module, and flashes during any I/O operation for the
module.
ACFAIL*
A VMEbus backplane line that is asserted under these conditions: 1) by the
mainframe Power Supply when a power failure has occurred (either ac line
source or power supply malfunction), or 2) by the front panel ON/
STANDBY switch when switched to STANDBY.
A-Size Card
A VXIbus instrument module that is 100.0 × 160 mm × 20.32 mm (3.9 ×
6.3 in × 0.8 in), the same size as a VMEbus single-height short module.
Asynchronous Communication
Communications that occur outside the normal “command-response” cycle.
Such communications have higher priority than synchronous communica-
tion.
Backplane
The printed circuit board that is mounted in a VXIbus mainframe to provide
the interface between VXIbus modules and between those modules and the
external system.
B-Size Card
A VXIbus instrument module that is 233.4 × 160 mm × 20.32 mm (9.2 ×
6.3 in × 0.8 in), the same size as a VMEbus double-height short module.
Bus Arbitration
In the VMEbus interface, a system for resolving contention for service
among VMEbus Master devices on the VMEbus.
Bus Timer
A functional module that measures the duration of each data transfer on the
Data Transfer Bus (DTB) and terminates the DTB cycle if the duration is
excessive. Without the termination capability of this module, a Bus Master
attempt to transfer data to or from a non-existent Slave location could result
in an infinitely long wait for the Slave response.