VTI Instruments EX1629, Руководство пользователя

Страница: 208 / 346

VTI Instruments Corp.
208 EX1629 Command Set
vtex1629_read_fifo
F
UNCTION
P
ROTOTYPE
ViStatus vtex1629_read_fifo (ViSession vi , ViInt32 maxscans , ViReal64 _VI_FAR seconds[] , ViReal64 _VI_FAR
nanoSeconds[] , ViPInt32 numscans , ViInt32 maxdata , ViReal64 _VI_FAR data[] , ViPInt32 numdata , ViInt32
to_secs );
F
UNCTION
P
ARAMETERS
vi = contains a session handle to the instrument. This handle is obtained by the function and remains valid until the
session is closed.
maxscans = an integer input value indicating the maximum number of scans that the function should return from the
EX1629. Valid input values: 1 to 10,000.
seconds = a returned array of real numbers. Each element in the array contains a time stamp, in seconds (s),
corresponding to a single scan taken by the instrument.
nanoSeconds = a returned array of real numbers. Each element in the array contains a time stamp, in nanoseconds
(ns), corresponding to a single scan taken by the instrument.
numscans = a returned integer value indicating the number of scans actually returned by the function call.
maxdata = an integer input value indicating the maximum length of the data array.
data = a returned array of real numbers that contains data sampled from the main inputs.
numdata = an integer return value indicating the number of data elements actually returned in the data array.
to_secs = an integer input value indicating the time, in seconds, that the function will spend retrieving data from the
EX1629 before timing out and returning (timeout). If a zero is passed for this parameter, the timeout period is
infinite.
D
ATA
I
TEM
R
ESET
V
ALUE
Not applicable to this function.
D
ESCRIPTION
This function retrieves data from the instrument’s FIFO (First In, First Out) buffer. Once data is retrieved, the data is
permanently erased from the EX1629. The following data is returned by this function:
• Data timestamps in seconds (s) and nanoseconds (ns)
• Number of scans returned
• Sampled data from the main inputs • Number of data points returned
Data items from the
data parameter are organized in the array according to the scan list set at the time of data
acquisition. For example, if channels 0 - 15 are the scan list channels at the time of acquisition, then after a
vtex1629_read_fifo function call is made, the first sixteen elements of the
data array will correspond to the data
from the first scan for channels 0 through 15 (if there is a second scan of data, the next sixteen elements would
contain the second scan, etc.).
For each scan of data returned, there will be one timestamp (a seconds and a nanoseconds value) and a number of
data values equal to the length of the scanlist. Assuming that the timestamp and data arrays are sized properly, the
number of data elements returned (
numdata ) will be equal to numscans multiplied by the scanlist length.
vtex1629_read_fifo will return as soon as either the
maxscans scans of data have been retrieved, or the timeout
( to_secs ) expires, whichever happens first.
There are other mechanisms for retrieving data from the EX1629. Please see
Retrieving Data (Read FIFO and
Streaming Data) for more information.