Hoist your aerial aloft and get tips from the Oracle
TELETEXT is an information service that is offered both by the
BBC and the IBA. They often use examples of it instead of the
test card - the BBC provides Ceefax, and the IBA Oracle.
The information is transmitted in numbered pages which can be
displayed one at a time on a suitable TV.
The signals for this service are digital and as such are obviously
perfect for use with a computer.
The Teletext adapter, like most other add-ons for the BBC Micro
was subject to delays.
Now that it's available and I've used one, I must admit that
for someone who hasn't had access to any of the Teletext facilities
before, it's addictive.
The adapter itself is in a box about half the width of the computer
and is shaped to form a single unit with the micro.
At the rear are four small tuning knobs, an aerial socket and
an on/off switch. The unit is powered from the mains and is connected
to the computer via the 1 MHz bus.
The software that forms the TFS (Telesoft Filing System) comes
in eprom. Once inserted as default filing system the machine starts
up with the message 'Acorn TFS'.
With TFS and DFS the OSHWM is &2A00, so the first thing
to do was to find out how I could still use the computer when
not using the TFS.
This is simply achieved by turning off the power to the Teletext
unit and performing a hard BREAK. The message 'Acorn TFS no power'
comes up and OSHWM is &1900 once again. Nice and easy, that!
Next step was getting down to use the TFS. The first problem
was that I didn't have an aerial. I live very close to a repeater
and I normally just use a loop aerial on my TV.
One of the appendices in the manual gives two pages of information
about Teletext reception and was very useful.
I ignored all this and fitted a simple internal UHF aerial and
luckily everything was OK.
It would seem that to receive Teletext properly relies on a
very "clean" TV signal so if you live in a fringe area
for TV reception you could have difficulties.
A point to mention here is that you do need the relevant class
of licence to receive Teletext even on a monitor, so if you don't
own a TV or you've got a monochrome licence and a colour monitor
it's going to cost you!
The TFS will operate in two main modes, the Terminal mode and
the Telesoft mode.
In Terminal mode you have virtually all the facilities of an
intelligent Teletext receiver at your disposal.
There is a tuning facility, pages can be linked, and pages can
be stored to any other filing system available to the user.
An added extra is that you can also look at and load the computer
programs that the BBC Telesoftware Service broadcast.
Telesoft mode is specifically for dealing with Telesoftware,
although it does have commands in common with Terminal mode. Telesoft
should be thought of as a read-only filing system.
The manual that comes with the adapter is excellent. It includes
all the information that is necessary to use the system at any
level, from assembler level to naive user.
There are also 23 pages of technical information for anyone
interested in the complexities of Teletext. They make very interesting
reading for someone who doesn't know anything about it.
All in all I enjoyed using this add-on. The only problems I
can see are those of reception, but a well installed aerial should
cure these.
At £225 it's a bit expensive for the home user, especially
as there doesn't seem to be much Telesoftware available, although
I suppose the service is in its infancy.
Alan Plume
