Glossary
VME-MXI-2 User Manual
Glossary-2
© National Instruments Corporation
A24/A32 Decoder
The logic circuit on the VME-MXI-2 that is responsible for
detecting data transfers to the module’s registers or DRAM in
A24 or A32 address space.
A24 space
The VME 16 MB standard address space.
A32 space
The VME 4 GB extended address space.
ACFAIL
A VMEbus backplane signal that is asserted when a power
failure has occurred (either AC line source or power supply
malfunction), or if it is necessary to disable the power supply
(such as for a high temperature condition).
address
Character code that identifies a specific location (or series of
locations) in memory.
address modifier
One of six signals in the VMEbus specification used by
VMEbus masters to indicate the address space in which a data
transfer is to take place.
address space
A set of 2n memory locations differentiated from other such sets
in VMEbus systems by six addressing lines known as address
modifiers. n is the number of address lines required to uniquely
specify a byte location in a given space. Valid numbers for n are
16, 24, and 32. In VME, because there are six address modifiers,
there are 64 possible address spaces.
address window
A portion of address space that can be accessed from the
application program.
ANSI
American National Standards Institute
arbiter
Circuitry providing the bus arbitration mechanism for a system.
arbitration
A process in which a potential bus master gains control over a
particular bus.
asynchronous
Not synchronized; not controlled by time signals.
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