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| >Video for Linux Two API Specification: Revision 0.24</TH |
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| >Chapter 4. Interfaces</TD |
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| >4.9. Teletext Interface</A |
| ></H1 |
| ><P |
| >This interface aims at devices receiving and demodulating |
| Teletext data [<A |
| HREF="b17127.htm#ETS300706" |
| ><ABBR |
| CLASS="ABBREV" |
| >ETS 300 706</ABBR |
| ></A |
| >, <A |
| HREF="b17127.htm#ITU653" |
| ><ABBR |
| CLASS="ABBREV" |
| >ITU BT.653</ABBR |
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| >], 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 <TT |
| CLASS="FILENAME" |
| >linux/videotext.h</TT |
| >, the |
| specification is available from <A |
| HREF="http://home.pages.de/~videotext/" |
| TARGET="_top" |
| >http://home.pages.de/~videotext/</A |
| >. (Videotext is the name of |
| the German public television Teletext service.) Conventional character |
| device file names are <TT |
| CLASS="FILENAME" |
| >/dev/vtx</TT |
| > and |
| <TT |
| CLASS="FILENAME" |
| >/dev/vttuner</TT |
| >, 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 |
| <TT |
| CLASS="FILENAME" |
| >/dev/tlkN</TT |
| >, device number 102, N.</P |
| ><P |
| >Eventually the Teletext API was integrated into the V4L API |
| with character device file names <TT |
| CLASS="FILENAME" |
| >/dev/vtx0</TT |
| > to |
| <TT |
| CLASS="FILENAME" |
| >/dev/vtx31</TT |
| >, 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 Video4Linux mailing list: <A |
| HREF="https://listman.redhat.com/mailman/listinfo/video4linux-list" |
| TARGET="_top" |
| >https://listman.redhat.com/mailman/listinfo/video4linux-list</A |
| > |
| when the need arises.</P |
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