Easier teletext
John Harris evaluates a replacement for the Acorn teletext
adapter's TFS rom
THE Advanced Teletext System (ATS) rom from BBC Soft replaces
the Teletext Filing System (TFS) rom originally supplied with
Acorn's Teletext Adapter.
There are five main advantages that the ATS has over the TFS.
You select pages by their numbers only, rather than having to
press f0 first. Links between pages (now being broadcast by both
BBC and ITV) are used to give a bottom line menu of four pages
linked to the currently displayed page.
Linked pages are automatically stored in the computer as they
are broadcast, so that they become instantly available.
The downloading of files is improved. And all broadcast data
can be made available to your programs.
When using the system as a teletext terminal (like a teletext
TV), you can select pages by entering the three-digit page number.
With the TFS you have to prefix these three digits by pressing
a function key (f0 - Select Page).
The old TFS accepts unprefixed number keys as link numbers,
based on a hierarchical structure of linked pages. But the TFS
was produced before the broadcasting authorities had finalised
how these broadcast links would be implemented.
In practice few pages can be organised into strict hierarchies
and the final implementation is much simpler. And the ATS makes
full use of the new system.
There are several links, of which four are directly available
in the form of four menu items — these are coloured red, green,
yellow and blue. On the function key label f1 to f4 are patches
of these colours.
The corresponding items on the screen are either the page numbers
these keys select, or textual data sent by the teletext editors
who prepare the information for broadcasting.
One of the links is to an index page using fO, but which index
it gives you depends on the teletext editors. It may give you
the nearest sub-index, the main index for the channel, or the
alphabetical subject index.
The average time taken to receive a page, once it has been selected,
depends on the interval between successive transmissions of the
same page. However, if the teletext receiver stores the pages
in ram before you select them, they can appear almost instantaneously.
There isn't sufficient ram in the BBC Micro to store the hundreds
of pages broadcast on a channel, but the TFS allows you to select
several to be continuously stored in ram and updated as broadcast.
The ATS has this facility as well (now on the Copy key), but
also captures pages linked to the current page. As the links are
on frequently-used routes (such as from index to sub-index and
from headlines to news stories), average waiting time is cut dramatically.
The ATS also stores the page or sub-page received just before
the one currently displayed. It can easily be restored to the
screen with the Tab key - a relief when the sub-page you're reading
is overwritten by the next one. You can toggle back again, also
using the Tab key.
Pressing Return gives you a screenful of information on the
page numbers of the current page (but not sub-page), links one
to five, the index link, the first seven stored pages and the
next. But I couldn't find an explanation of this in the guide.
This use of Return conflicts with its conventional use as a
terminator. Such disregard of conventions is all too frequent
and makes the use of computers frustrating and error-prone. To
return to the current page, press the spacebar.
The TFS was designed to download broadcast *EXEC files - in
other words the BBC Micro accepted them as if they had been typed
at the keyboard. Only Basic programs could be downloaded, and
then in an inefficient (untokenised) form.
To remedy this the BBC broadcast a patch program that allowed
the TFS to load tokenised Basic programs and to *LOAD text, machine
code, screen dumps or anything that could be loaded straight into
the micro's memory. The problem was that you had to store this
patch on a disc or tape and load it each time you started a telesoftware
session.
The ATS does away with all such problems. Pressing f5 downloads
a catalogue of the files being broadcast on the current channel.
This may take quite a few seconds because the ATS finds the page
containing the information via a link on the main index page.
The catalogue appears on the screen together with instructions
on how to select files for downloading. It operates as a scrollable
menu and the software takes care of downloading it in the appropriate
way for the type of file chosen.
In contrast to the TFS, the ATS keeps you informed about what
you are ATS link menu On the bottom line of a teletext screen
downloading. It displays the filename (as in the broadcast catalogue
and used to save the downloaded file), the load and execute addresses,
the number of blocks in the file and how many have so far been
received successfully.
Each block of the file is also shown as a white square that
turns green when it's successfully received, or red if there's
an error, in which case the ATS will try again. An arrow shows
which block was last received.
This is a vast improvement over the TFS. But it would be even
better if you could select in one go all the files you want to
download. You could leave the ATS to get on with it - something
for the next release, perhaps.
There have been several changes to the * commands (called telesoft
mode commands on the TFS and teletext operating system commands
on the ATS). The ATS uses *TTX and *NOTTX to switch the adapter
on and off. The prefix T can be used to avoid clashes with commands
in other roms.
There are other new commands: *DATA allows the full data of
a page (2k) to be transferred to a given memory address. With
this your programs have access to all the broadcast data. *S4C
is provided as an alternative to *CH4 and *ITV2 for Welsh users.
You can also type *MAGAZINE to stop the page numbers in the
header flickering (when two or more magazines are broadcast in
parallel). Only the selected magazine's page numbers are displayed.
There are changes in how TRANSFER and *DISPLAY operate but *TELETEXT
restores them to compatiblility with the TFS.
The undocumented commands *HON and *HOFF in the TFS are now
documented in the ATS guide. Because the ATS isn't treated as
a filing system, it doesn't use the TFS commands *EXEC and *OPT.
I have found three places where the TFS still scores over the
ATS. It allows wildcards to be used in page number selections.
This is useful when, for example, you see that an unusual page
number, say between 890 and 899, is being broadcast and it isn't
given in an index.
It's often difficult to see the exact page number, as the last
figure is overwritten so fast. Being nosey, I use the wildcard
to select. In this case 89# will show what's being broadcast.
With the TFS you can use the Copy key to see which sub-page
is currently displayed. I found no such facility on the ATS.
And there is a bug in the ATS. If the current page is rebroadcast
after you've started (but haven't finished) entering a new page
number, the number of the current page is reinstated over the
figure or figures you've entered and you have to start again.
Luckily this doesn't happen very often, but it's very irritating
when it does. Let's hope this will be put right in future versions.
But apart from this little bug the ATS is a great improvement
on the TFS and is well worth the amazingly cheap price -which
also includes a 64-page user guide.
Product: ATS rom
Price: £7.95
Supplier: BBC Soft, 35 Marylebone High Street, London W1M 4AA.
Tel: 01-580 5577
ATS link menu on the bottom line of a teletext screen
