linux-vybrid_public/Documentation/DocBook/v4l/dev-teletext.xml

  <title>Teletext Interface</title>

  <para>This interface aims at devices receiving and demodulating
Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the
Teletext packages and storing formatted pages in cache memory. Such
devices are usually implemented as microcontrollers with serial
interface (I<superscript>2</superscript>C) and can be found on older
TV cards, dedicated Teletext decoding cards and home-brew devices
connected to the PC parallel port.</para>

  <para>The Teletext API was designed by Martin Buck. It is defined in
the kernel header file <filename>linux/videotext.h</filename>, the
specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/">
ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of
the German public television Teletext service.) Conventional character
device file names are <filename>/dev/vtx</filename> and
<filename>/dev/vttuner</filename>, 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
<filename>/dev/tlkN</filename>, device number 102, N.</para>

  <para>Eventually the Teletext API was integrated into the V4L API
with character device file names <filename>/dev/vtx0</filename> to
<filename>/dev/vtx31</filename>, 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.</para>

  <para>There are no plans to replace the Teletext API or to integrate
it into V4L2. Please write to the linux-media mailing list: &v4l-ml;
when the need arises.</para>

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