teletext

Text-only version of the internet that's been accessable through TV sets in the UK for many many years. Usually carries TV guides, national and local news and lots of stuff no-one ever reads. Now becoming obsolete.

The version in New Zealand is rather depressing - the editors seem to have taken a nap for the past 5 years. Often I see writeups with large consistency errors and speling mistakes. Just like the internet really, or my nodes. Of course, I'm not being paid for my time editing...

Plus due to so- called popular demand, the English Football League results and standings are now not only on the slowest page turnover, but all on the same page! And only updated on Fridays!! That's popular demand for you nowadays.

p.s. The newest of the standard channels doesn't even broadcast teletext, so I can't even check the news during the adverts that invade the space between more adverts.

Teletext is hardly comparable to the internet for one simple reason: it's a one-way medium (although with some very complex page programming and a bit of social engineering to persuade the viewer to pick up their telephone it can be made interactive in a very crude way).

That having been said, if a technology which was invented in the early 1980s is still in widespread and general usage today it must be doing something right. Teletext works by inserting data into the unused scan lines which appear above and below the broadcast picture on any TV set. In other words, your TV can display 625 lines of image, but the TV companies actually broadcast 640. Some of these "unused" lines carry control signals to help the TV keep its picture tuned-in and synchronised, but there are some spare lines.

Teletext is based around a 40x25 text-only display (although it has some block graphics similar to those from ANSI DOS), and each of these 1000-byte pages (actually a full kilobyte due to transmission of parity check bytes and other control information) is numbered between 100 and 799. Using special remote control handsets viewers can select these pages, either by keying in the correct number or by following a series of coloured menus.

Common applications include: news, TV guide and subtitles on programmes for the hard-of-hearing. In the UK at least all of the terrestrial television channels carry very comprehensive pages covering all of the above and much more, as well as most of the larger satellite and cable channels. Many of the pages carry local content which is inserted by the particular regional TV station making the actual transmission. This means you could be watching a programme on BBC1, for example, while still reading the news local to your region on teletext.

Despite being potentially threatened by the arrival and popular uptake of Digital Television and the internet, both of which allow full interactivity at greater graphics resolutions, teletext is such a simple and well-known system that it's unlikely to vanish any time soon. I for one am glad of that: despite having access to all sorts of information resources I still find it easier to turn on my TV, pick up the remote and press <Text><Yellow> to get up-to-date news headlines than anything else.

Teletext is a 40 column by 25 line standard for broadcasting textual information alongside a television signal. The "carousel" (meaning all the pages being transmitted) is broken up into "magazines" (being a set of pages with the same initial digit). Each page within a magazine has a three digit identifier, with "x00" being the magazine index.

To enable articles to span more than a single screenful, pages are made up of "frames", all with the same page number but a different "subpage" number. For example, Lloyds TSB shares might be on BBC2 Ceefax page 222, subpage 0002.

Each cell can contain an alphanumeric character, a graphic character or a control code.

Graphic characters are based on a 3 high by 2 wide grid (with the grid elements either solid or "separated").

Control codes are things such as "red", "set background", "double height", "white", "hidden", etc.

The same display standard is used in Viewdata, which has fallen by the wayside of computer history.

Control codes for teletext are precisely the BBC Microcomputer's MODE 7 control codes (it was designed with the teletext adaptor in mind). Every control code requires a cell, so if you want to switch e.g. to blinking yellow text, 2 blank spaces will show up.

Codes include double height (but you had to start on an even row!), foreground and background colours, and even graphics. In graphics, each character cell is divided into 6 boxes (3 rows, 2 columns); total resolution is 80x75, but generally you mix text and graphics. Each box can be controlled separately, but they must all have the same colour! There's also provision for having the boxes noncontiguous, so you get your pixels with a background-coloured boundary around them.

Designing good teletext pages is something of an art. The BBC even had games written for this mode -- mostly clones of old Atari 2600 games (Space Invaders, Snake, and the like). Storing an entire page of teletext mode requires just 40x25 = 1000 bytes, or under 1K. If you consider that it's hard to read 80 column text on a TV set, you begin to understand the engineering appeal of teletext.

The real killer of teletext wasn't the technology; it was the content. Most broadcasters just repeated their news headlines (and stories) on the teletext pages; why waste your time reading the headlines from your TV set, when you can get somebody with excellent diction to read them out to you while you're brushing your teeth?