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Glossary
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National Instruments Corporation
G-5
PCI/PXI-1408 and NI-IMAQ for Win95/NT
DMA
direct memory access—a method by which data can be transferred
to and from computer memory from and to a device or memory on
the bus while the processor does something else; DMA is the
fastest method of transferring data to/from computer memory
DRAM
dynamic RAM
drivers
software that controls a specific hardware device such as an
IMAQ or DAQ device.
dynamic range
the ratio of the largest signal level a circuit can handle to the
smallest signal level it can handle (usually taken to be the noise
level), normally expressed in dB
E
EEPROM
electrically erasable programmable read-only memory—ROM
that can be erased with an electrical signal and reprogrammed
external trigger
a voltage pulse from an external source that triggers an event such
as A/D conversion
F
field
For an interlaced video signal, a field is half the number of
horizontal lines needed to represent a frame of video; the first
field of a frame contains all the odd-numbered lines, the second
field contains all of the even-numbered lines.
FIFO
first-in first-out memory buffer—the first data stored is the first
data sent to the acceptor; FIFOs are used on IMAQ devices to
temporarily store incoming data until that data can be retrieved.
For example, an analog input FIFO stores the results of A/D
conversions until the data can be retrieved into system memory,
a process that requires the servicing of interrupts and often the
programming of the DMA controller. This process can take
several milliseconds in some cases. During this time, data
accumulates in the FIFO for future retrieval.
flash ADC
an ADC whose output code is determined in a single step by a
bank of comparators and encoding logic