National Instruments DAQ X Series User Manual page 272

Glossary
DC Direct current—although the term speaks of current, many different types
of DC measurements are made, including DC Voltage, DC current, and DC
power.
device An electronic board that performs general analog or digital I/O functions
on one or multiple channels, connected to a PC through a bus or I/O port,
such as PCI, PXI, Ethernet, USB, or serial.
DIFF Differential mode—An analog input mode consisting of two terminals,
both of which are isolated from computer ground, whose difference is
measured.
differential input An input circuit that actively responds to the difference between
two terminals, rather than the difference between one terminal and ground.
Often associated with balanced input circuitry, but also may be used with
an unbalanced source.
digital I/O The capability of an instrument to generate and acquire digital signals.
Static digital I/O refers to signals where the values are set and held, or
rarely change. Dynamic digital I/O refers to digital systems where the
signals are continuously changing, often at multi-MHz clock rates.
digital trigger A TTL level signal having two discrete levels—A high and a low level.
DMA Direct Memory Access—A method by which data can be transferred
to/from computer memory from/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.
DMA controller chip Performs the transfers between memory and I/O devices independently of
the CPU.
driver Software unique to the device or type of device, and includes the set of
commands the device accepts.
E
edge detection A technique that locates an edge of an analog signal, such as the edge of a
square wave.
EEPROM Electrically Erasable Programmable Read-Only Memory—ROM that can
be erased with an electrical signal and reprogrammed. Some SCXI modules
contain an EEPROM to store measurement-correction coefficients.
X Series User Manual
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