'\" t
.\"     Title: comedi_data_read
.\"    Author: David Schleef <ds@schleef.org>
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 12/30/2018
.\"    Manual: Comedi reference
.\"    Source: Comedi
.\"  Language: English
.\"
.TH "COMEDI_DATA_READ" "3" "12/30/2018" "Comedi" "Comedi reference"
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.SH "NAME"
comedi_data_read \- read single sample from channel
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <comedilib\&.h>
.fi
.ft
.HP \w'int\ comedi_data_read('u
.BI "int comedi_data_read(comedi_t\ *\ " "device" ", unsigned\ int\ " "subdevice" ", unsigned\ int\ " "channel" ", unsigned\ int\ " "range" ", unsigned\ int\ " "aref" ", lsampl_t\ *\ " "data" ");"
.SH "DESCRIPTION"
.PP
Reads a single sample on the channel specified by the Comedi device
\fIdevice\fR, the subdevice
\fIsubdevice\fR, and the channel
\fIchannel\fR\&. For the A/D conversion (if appropriate), the device is configured to use range specification
\fIrange\fR
and (if appropriate) analog reference type
\fIaref\fR\&. Analog reference types that are not supported by the device are silently ignored\&.
.PP
The function
\fBcomedi_data_read\fR
reads one data value from the specified channel and stores the value in
*\fIdata\fR\&.
.PP
WARNING:
\fBcomedi_data_read\fR
does not do any pausing to allow multiplexed analog inputs to settle before starting an analog to digital conversion\&. If you are switching between different channels and need to allow your analog input to settle for an accurate reading, use
\fBcomedi_data_read_delayed\fR, or set the input channel at an earlier time with
\fBcomedi_data_read_hint\fR\&.
.PP
Data values returned by this function are unsigned integers less than or equal to the maximum sample value of the channel, which can be determined using the function
\fBcomedi_get_maxdata\fR\&. Conversion of data values to physical units can be performed by the functions
\fBcomedi_to_phys\fR
(linear conversion) or
\fBcomedi_to_physical\fR
(non\-linear polynomial conversion)\&.
.SH "RETURN VALUE"
.PP
On success,
\fBcomedi_data_read\fR
returns
1
(the number of samples read)\&. If there is an error,
\-1
is returned\&.
.PP
.SH "AUTHORS"
.PP
\fBDavid Schleef\fR <\&ds@schleef.org\&>
.RS 4
Author.
.RE
.PP
\fBFrank Mori Hess\fR <\&fmhess@users.sourceforge.net\&>
.RS 4
Author.
.RE
.PP
\fBHerman Bruyninckx\fR <\&Herman.Bruyninckx@mech.kuleuven.ac.be\&>
.RS 4
Author.
.RE
.PP
\fBBernd Porr\fR <\&tech@linux-usb-daq.co.uk\&>
.RS 4
Author.
.RE
.PP
\fBIan Abbott\fR <\&abbotti@mev.co.uk\&>
.RS 4
Author.
.RE
.PP
\fB\('Eric Piel\fR <\&piel@delmic.com\&>
.RS 4
Author.
.RE
.SH "COPYRIGHT"
.br
Copyright \(co 1998-2003 David Schleef
.br
Copyright \(co 2001-2003, 2005, 2008 Frank Mori Hess
.br
Copyright \(co 2002-2003 Herman Bruyninckx
.br
Copyright \(co 2012 Bernd Porr
.br
Copyright \(co 2012 Ian Abbott
.br
Copyright \(co 2012, 2015 \('Eric Piel
.br
.PP
This document is part of Comedilib. In the context of this document, the term "source code" as defined by the license is interpreted as the XML source.
.PP
This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, version 2.1 of the License.
.PP
This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
.PP
You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
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