National Instruments 653 Series User Manual page 133

Glossary
device
DGND
digital trigger
DIO
DMA
DPULL
F
FIFO
function
G
group
NI 653X User Manual
A plug-in data acquisition board, card, or pad that can contain multiple
channels and conversion devices. Plug-in boards, PCMCIA cards, and
devices that connects to your computer parallel port, are all examples of
DAQ devices.
digital ground
A TTL-level signal having two discrete levels—a high and a low level.
digital input/output
Direct Memory Access—a method by which data can be transferred to or
from computer memory from or to a device or memory on the bus while the
processor does something else. DMA is the fastest method of transferring
data to or from computer memory.
A user-configurable 100 kΩ internal resistor for data lines. You can connect
the line to +5 VDC (pull up) or connect the line to ground (pull down).
First-In First-Out memory buffer—the first data stored is the first data sent
to the acceptor. FIFOs are often used on DAQ devices to temporarily store
incoming or outgoing data until that data can be retrieved or output. 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. With a larger FIFO,
longer latencies can be tolerated. In the case of analog output, a FIFO
permits faster update rates, because the waveform data can be stored on the
FIFO ahead of time. This again reduces the effect of latencies associated
with getting the data from system memory to the DAQ device.
A set of software instructions executed by a single line of code that may
have input and/or output parameters and returns a value when executed.
A collection of one, two, or four ports and an associated timing controller.
All buffered operations must be performed on groups.
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