media what died a'bornin'

From: Tony Duell <>
Date: Fri Oct 8 17:50:04 2004

> In the U.S., the "closed caption" system, which is primarily for
> text for hard of hearing folk, puts two bytes of ASCII into line 21
> of the VBI (vertical blanking interval). It CAN be used for other
> purposes.

This sounds very similar to the UK Teletext system (which is, indeed,
used to provide subtitles for deaf people, along with many 'pages' of
information). As I mentioned last night, this was used to distribute
software for the BBC micro.

Interesting thing : The page number is a 3 digit BCD number, but nowhere
in the hardware are the invald BCD nybbles (1010..1111) ever prohibited.
Pages with such numbers can't be selected on a normal TV, but can be
decoded and displayed by a computer-controller teletext decoder. And such
pagesd certainly exist...

Received on Fri Oct 08 2004 - 17:50:04 BST

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