Glossary
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National Instruments Corporation
G-5
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.
DNL
differential nonlinearity—a measure in least significant bit of the
worst-case deviation of code widths from their ideal value of 1 LSB
DO
digital output
E
EEPROM
electrically erasable programmable read-only memory—ROM that can be
erased with an electrical signal and reprogrammed
EXTREF
external reference signal
EXTSTROBE
external strobe signal
F
F
farads
FIFO
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.
floating signal sources
signal sources with voltage signals that are not connected to an absolute
reference or system ground. Also called nonreferenced signal sources.
Some common example of floating signal sources are batteries,
transformers, or thermocouples.
FREQ_OUT
frequency output signal
