1.. -*- coding: utf-8; mode: rst -*-
2
3.. _ttx:
4
5******************
6Teletext Interface
7******************
8
9This interface was aimed at devices receiving and demodulating Teletext
10data [:ref:`ets300706`, :ref:`itu653`], evaluating the Teletext
11packages and storing formatted pages in cache memory. Such devices are
12usually implemented as microcontrollers with serial interface
13(I:sup:`2`\ C) and could be found on old TV cards, dedicated Teletext
14decoding cards and home-brew devices connected to the PC parallel port.
15
16The Teletext API was designed by Martin Buck. It was defined in the
17kernel header file ``linux/videotext.h``, the specification is available
18from
19`ftp://ftp.gwdg.de/pub/linux/misc/videotext/ <ftp://ftp.gwdg.de/pub/linux/misc/videotext/>`__.
20(Videotext is the name of the German public television Teletext
21service.)
22
23Eventually the Teletext API was integrated into the V4L API with
24character device file names ``/dev/vtx0`` to ``/dev/vtx31``, device
25major number 81, minor numbers 192 to 223.
26
27However, teletext decoders were quickly replaced by more generic VBI
28demodulators and those dedicated teletext decoders no longer exist. For
29many years the vtx devices were still around, even though nobody used
30them. So the decision was made to finally remove support for the
31Teletext API in kernel 2.6.37.
32
33Modern devices all use the :ref:`raw <raw-vbi>` or
34:ref:`sliced` VBI API.
35