<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Teletext Interface</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API" /><link rel="up" href="ch04.html" title="Chapter 4. Interfaces" /><link rel="prev" href="ch04s08.html" title="Sliced VBI Data Interface" /><link rel="next" href="ch04s10.html" title="Radio Interface" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Teletext Interface</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s08.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Interfaces</th><td width="20%" align="right"> <a accesskey="n" href="ch04s10.html">Next</a></td></tr></table><hr /></div><div class="section" title="Teletext Interface"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="ttx"></a>Teletext Interface</h2></div></div></div><p>This interface aims at devices receiving and demodulating Teletext data [<a class="xref" href="bi01.html#ets300706" title="ETS 300 706 "Enhanced Teletext specification"">[<abbr class="abbrev">ETS 300 706</abbr>]</a>, <a class="xref" href="bi01.html#itu653" title="ITU-R Recommendation BT.653-3 "Teletext systems"">[<abbr class="abbrev">ITU BT.653</abbr>]</a>], evaluating the Teletext packages and storing formatted pages in cache memory. Such devices are usually implemented as microcontrollers with serial interface (I<sup>2</sup>C) and can be found on older TV cards, dedicated Teletext decoding cards and home-brew devices connected to the PC parallel port.</p><p>The Teletext API was designed by Martin Buck. It is defined in the kernel header file <code class="filename">linux/videotext.h</code>, the specification is available from <a class="ulink" href="ftp://ftp.gwdg.de/pub/linux/misc/videotext/" target="_top"> ftp://ftp.gwdg.de/pub/linux/misc/videotext/</a>. (Videotext is the name of the German public television Teletext service.) Conventional character device file names are <code class="filename">/dev/vtx</code> and <code class="filename">/dev/vttuner</code>, with device number 83, 0 and 83, 16 respectively. A similar interface exists for the Philips SAA5249 Teletext decoder [specification?] with character device file names <code class="filename">/dev/tlkN</code>, device number 102, N.</p><p>Eventually the Teletext API was integrated into the V4L API with character device file names <code class="filename">/dev/vtx0</code> to <code class="filename">/dev/vtx31</code>, device major number 81, minor numbers 192 to 223. For reference the V4L Teletext API specification is reproduced here in full: "Teletext interfaces talk the existing VTX API." Teletext devices with major number 83 and 102 will be removed in Linux 2.6.</p><p>There are no plans to replace the Teletext API or to integrate it into V4L2. Please write to the linux-media mailing list: <a class="ulink" href="http://www.linuxtv.org/lists.php" target="_top">http://www.linuxtv.org/lists.php</a> when the need arises.</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04s08.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch04.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch04s10.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Sliced VBI Data Interface </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Radio Interface</td></tr></table></div></body></html>
