1  <title>Teletext Interface</title>
2
3  <para>This interface was aimed at devices receiving and demodulating
4Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the
5Teletext packages and storing formatted pages in cache memory. Such
6devices are usually implemented as microcontrollers with serial
7interface (I<superscript>2</superscript>C) and could be found on old
8TV cards, dedicated Teletext decoding cards and home-brew devices
9connected to the PC parallel port.</para>
10
11  <para>The Teletext API was designed by Martin Buck. It was defined in
12the kernel header file <filename>linux/videotext.h</filename>, the
13specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/">
14ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of
15the German public television Teletext service.)</para>
16
17  <para>Eventually the Teletext API was integrated into the V4L API
18with character device file names <filename>/dev/vtx0</filename> to
19<filename>/dev/vtx31</filename>, device major number 81, minor numbers
20192 to 223.</para>
21
22  <para>However, teletext decoders were quickly replaced by more
23generic VBI demodulators and those dedicated teletext decoders no longer exist.
24For many years the vtx devices were still around, even though nobody used
25them. So the decision was made to finally remove support for the Teletext API in
26kernel 2.6.37.</para>
27
28  <para>Modern devices all use the <link linkend="raw-vbi">raw</link> or
29<link linkend="sliced">sliced</link> VBI API.</para>
30