Acorn teletext adapter

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
Post Reply
guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Acorn teletext adapter

Post by guesser » Tue Oct 30, 2018 8:50 pm

I've just received a working Acorn teletext adapter.
Does anyone have a scan of the Advanced Teletext System keystrip?

As a more general question has anyone made any attempt at documenting the ROM and researching/reverse engineering the "very complex" Redefinable Telesoftware format?
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

User avatar
tricky
Posts: 3811
Joined: Tue Jun 21, 2011 8:25 am
Contact:

Re: Acorn teletext adapter

Post by tricky » Tue Oct 30, 2018 8:58 pm

A bit off topic, but I just tried the teletext editor in your sig and it doesn't seem to handle different colour top and bottom halves of double height characters.
It also doesn't show the control codes when double height on the previous row would not show the characters, which I guess doesn't have a defined behaviour!

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Oct 30, 2018 9:02 pm

tricky wrote:
Tue Oct 30, 2018 8:58 pm
A bit off topic, but I just tried the teletext editor in your sig and it doesn't seem to handle different colour top and bottom halves of double height characters.
It also doesn't show the control codes when double height on the previous row would not show the characters, which I guess doesn't have a defined behaviour!
It's because it's a teletext editor, not a BBC mode 7 editor :)
In teletext the row below a row containing double height always takes the background colour of the top row and anything transmitted on the row below is ignored by the decoder.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.


guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Oct 30, 2018 10:34 pm

excellent thanks!
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

User avatar
tricky
Posts: 3811
Joined: Tue Jun 21, 2011 8:25 am
Contact:

Re: Acorn teletext adapter

Post by tricky » Wed Oct 31, 2018 12:17 am

guesser wrote:
Tue Oct 30, 2018 9:02 pm
tricky wrote:
Tue Oct 30, 2018 8:58 pm
A bit off topic, but I just tried the teletext editor in your sig and it doesn't seem to handle different colour top and bottom halves of double height characters.
It also doesn't show the control codes when double height on the previous row would not show the characters, which I guess doesn't have a defined behaviour!
It's because it's a teletext editor, not a BBC mode 7 editor :)
In teletext the row below a row containing double height always takes the background colour of the top row and anything transmitted on the row below is ignored by the decoder.
I nearly said that, and haven't checked this, but as the codes are in "memory", won't they get saved as a "mode 7 screen" which then won't look the same?
Still, it seems like a really nice editor (I'm always looking for a better way to edit my splash screens).

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Wed Oct 31, 2018 1:59 am

When exporting a BBC screen dump, the editor duplicates the contents of double height rows so that the bottom half isn't missing or different.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

User avatar
Multiwizard
Posts: 1666
Joined: Wed Jan 11, 2012 9:03 pm
Contact:

Re: Acorn teletext adapter

Post by Multiwizard » Wed Oct 31, 2018 7:16 am

Hi,

here's my successful attempt from last year to get it all work... :-D

https://www.youtube.com/watch?v=N4J16v7-NWc


Greetings, Wim... :-)

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Wed Oct 31, 2018 9:12 am

A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Wed Oct 31, 2018 11:56 am

Hmm, the original Acorn Teletext System User Guide includes a description of the Telesoftware format which seems to make sense along with a screenshot on mb21. I had some vague notion that the BBC altered the format at some point and provided a new downloader via telesoftware but I can't now find any reference to that.

Edit: aha, found it on a Ceefax recovery from 1984...
PATCH0
(Acorn)

This program creates an upgrade for
the Telesoft Filing System.

Download thj program, typj *DISC or
*TAPE thjn RUN it. A machine-code
routine calleh TSOFT will b— produced
on disc or tapj. Once this has been
obtained, typing *TSOFT (disc) or
*/TSOFT (tap—) instead of *TELESOFT
will allow thj us— of th— additional
commands LOAD, CHAIN, *LOAD and *TZPE
Try using *CAT.

All programs shown by a + on *CAT
must be downloaded using TSOFT, and
according to instructions on *INFO.
Last edited by guesser on Wed Oct 31, 2018 1:10 pm, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Sat Nov 03, 2018 1:15 am

So I forgot to post an update on here with what I've figured out and got working so far.

The changes to telesoftware appear to have been just in the data sent, presumably a different catalogue format or something. I've also been sent a scan of a document with a more detailed specification for RTF which confirms what I'd already decided that there's an error in the Acorn manual (or in the PDF I've been working from - need to check the paper copy tomorrow).

I'd already managed to massage the corrupted bytes from a 1988 teletext recovery enough in a hex editor to get it to load the telesoftware catalogue: https://twitter.com/ZXGuesser/status/10 ... 3433391105

My main efforts today were getting vbit2 generating teletext that ATS 3.0 doesn't get befuddled by. The main issue turned out to be because it wasn't quite meeting the specification with regards to the page erase interval, meaning that the first data row of a page was arriving just slightly earlier than the mandated 20ms. The few tens of microseconds was apparently enough to upset ATS however. With that issue "fixed" it no longer does weird things like the row occasionally appearing on a different page!

I have another tangentially related problem which I'm as yet unable to even come up with a theories to test. I've written a script to dump packet data from vbit2 at the appropriate rate into a file mimicking the format generated by Microsoft's WST codec, which BeebEm uses for teletext emulation. If I play these files back in BeebEm it fails quite spectacularly with row 2 and the whole lower half of the page missing for all the pages in magazine 1 of the page set I'm testing with. The same file converted to raw 42 byte packets and played out into the real adapter works perfectly.
I'll hopefully figure out what's going wrong, but in the longer term I would quite like to get an interface built into BeebEm to allow some form of interprocess communication to feed a stream of live teletext data in rather than looping obscure dump files. (I need to do the same thing with the Fuse emulator for the ZX Spectrum too, so hopefully a nice platform agnostic and well thought out communications protocol so the same teletext->emulator bridging utility can be used for each!)
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Nov 06, 2018 1:44 pm

I've re-done the keystrip as a vector file: https://zxnet.co.uk/teletext/documents/ ... ystrip.pdf

It's not an exact clone because the original is very hand-made and wonky, so I took the liberty of squaring everything up and making the grid regular etc. I copied the random changes in font size though :)

I've not printed out a test copy to make sure it's the correct scale yet.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

User avatar
paulv
Posts: 3854
Joined: Tue Jan 25, 2011 6:37 pm
Location: Leicestershire
Contact:

Re: Acorn teletext adapter

Post by paulv » Tue Nov 06, 2018 8:12 pm

guesser wrote:
Tue Nov 06, 2018 1:44 pm
I've re-done the keystrip as a vector file: https://zxnet.co.uk/teletext/documents/ ... ystrip.pdf
Would you mind if I host this on the retro-kit site too with proper attribution to you?

Paul

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Nov 06, 2018 10:13 pm

paulv wrote:
Tue Nov 06, 2018 8:12 pm
Would you mind if I host this on the retro-kit site too with proper attribution to you?
Not at all. Ideally somebody should take a direct measurement off a real one to ensure that I've not copied a scaling error from the scan though. It seems to me as though the overall width of the grid area is slightly narrower than the ten function keys.
Last edited by guesser on Tue Nov 06, 2018 10:38 pm, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Nov 06, 2018 10:45 pm

I've done a quick test print and as predicted it's all too short so things don't line up.
Also I've never cut out an original keyboard strip, so maybe this is normal, but it's vastly taller than it needs to be for the model B. If I scale up to get the length right that'll get even worse. Is this usual that you have to trim off a fairly wide strip above the text or is it just this particular example they've printed a lot of bleed?
Last edited by guesser on Tue Nov 06, 2018 10:48 pm, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

User avatar
AndyF
Posts: 1276
Joined: Sat Feb 23, 2008 10:16 pm
Location: Derby
Contact:

Re: Acorn teletext adapter

Post by AndyF » Thu Nov 08, 2018 9:50 am

Although slightly off topic, I had one of these not that long ago, maybe about two years back. I did sell it along with a few other items I did not require at the time, although I did have a very vague idea of selling its internals and keeping the 'cheese-wedge' case for other projects but decided not to bother with that, figuring the Text Adaptor was worth more complete. My thinking was simply the case (along with co pro ones) was ideal for 'other things'
Andy

* NEW * The Jetset Willy and Manic Miner community :)

Adventure games ported across to the BBC (in progress) as soon as I can find some time!

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Thu Nov 08, 2018 12:51 pm

It makes me sad that people do gut them for the cases to stick a Raspberry Pi coprocessor in etc. Sadly to a lot of people they aren't worth anything as they aren't even aware of the various teletext projects out there that can breathe life into them once again and just assume they've been a paperweight since Ceefax closed down. (I won't say make them useful again but you know what I mean :) )
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Thu Nov 08, 2018 2:44 pm

Right, I've tweaked the scaling of my vector keystrip so it's now a more appropriate size and lines up with the keys properly. Again I can't say it's 100% accurate to anything, but it looks right which is what I was aiming for :)

(updated PDF at the same link as before)
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

gtoal
Posts: 17
Joined: Sat Nov 04, 2017 2:07 am
Contact:

Re: Acorn teletext adapter

Post by gtoal » Fri Nov 09, 2018 9:11 pm

Thanks to my old pal Harry Barman for alerting me to this thread. I was the developer who worked on the released Teletext rom for Acorn and I still have the source code on a floppy. As it happens I'm currently putting together a Beeb system with a flashfloppy so I can copy off all my old disks, though I've found everything I need in my garden shed except my working (when I saw it last) US Beeb!

Any questions about teletext/telesoftware I'll do my best to answer.

I do still have some hardware but I don't think anyone over here is broadcasting anything. Shouldn't be too hard to intercept the low level OSWORD calls to the receiver however and inject some fake teletext data from that project I noticed recently that was resurrecting it.

By the way the source was originally in Beeb Basic embedded assembler and then I converted it (I think by version 1.2?) to the stand-alone assembler - with a binary check on the generated roms to ensure they were bit-identical. I ought to have both versions somewhere.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Fri Nov 09, 2018 9:55 pm

:o

I'm sure I will have plenty of questions over the coming weeks!

Is that the first ROM, or the ATS? Either way, original source sure beats learning 6502 and disassembling it! :D
No-one is broadcasting teletext in the UK any more, and on the continent it's all on digital now, but if you have a raspberry pi you can use vbit2 and raspi-teletext to output the community-run Teefax service as a teletext signal and either bypass the tuner in the adapter with a composite input, or use a UHF modulator.
I'm planning to add a telesoftware section to Teefax once I'm a bit further along with my experiments and write some conversion scripts to generate the pages. :)
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

gtoal
Posts: 17
Joined: Sat Nov 04, 2017 2:07 am
Contact:

Re: Acorn teletext adapter

Post by gtoal » Sat Nov 10, 2018 12:41 am

I guess the original - I think it identified as "TFS"? (It's been a long time since I thought about it!)

I *may* have a paper copy of the BBC's telesoftware definition document. I didn't write the telesoftware decoder though.

Anyway if you can generate packets with the same content of what would be transmitted over air, I'm fairly sure you don't need a hardware teletext receiver to decode them - just the ROM and a Beeb (or emulator). It fetches the low-level packets via an OSWORD which you can intercept and insert your own data. There are commands for changing channel etc as well, so you might be able to create an internet-based service sending data out over UDP or some sort of non-handshaked broadcast, and decode it as if it had been received off-air.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Sat Nov 10, 2018 1:01 am

Ok, I've not played with TFS, I've got the ATS ROMs, and besides historical curiosity there doesn't seem to be any reason you'd want to run the earlier one, but the source should definitely be preserved and archived regardless :)

Someone sent me a scan of some documentation which has excerpts from a specification. It was OCRed but not particularly well, so I re-edited it into something a bit easier to read and uploaded it here: https://zxnet.co.uk/teletext/documents/ ... 0Fixed.pdf
If you have more documentation that would be great, though I'm pretty sure I have enough information to start producing telesoftware downloads now. A lot of the info is in the TFS manual.

BeebEm has emulation of the adapter anyway. The current code reads from packet dump files and loops over them, but I'm currently hacking away at some code to enable feeding it a live packet stream in realtime. It's already working well I just need to clean all the code up to something resembling good enough to upload, I started a thread about it in the emulators section.

I started off with UDP, and the original author of the code had some plans to do that, but packets arriving out of order etc is a problem and rather than reinvent the wheel I switched to a TCP stream. It could send packets out across the internet but the bandwidth required is fairly horrendous so it's probably better suited to keeping it on the LAN or localhost.

Here's a screenshot I posted in the emulators section of 12 simultaneous instances all receiving synchronised teletext data from a little server I wrote in python:
Image
Last edited by guesser on Sat Nov 10, 2018 1:09 am, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Sun Nov 11, 2018 6:08 pm

Experimenting with my own telesoftware catalogue today:
foo.png
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Nov 13, 2018 1:37 am

I'm fairly sure this has been asked before, but does anyone have a schematic for the teletext adapter?
It appears that the operation of the hardware isn't as well understood as I'd assumed, because the code in BeebEm works with the ATS ROM, but not the original TFS. I think it's making a bad assumption about hardware bits based on observation of the ATS ROM's behaviour.

Edit: found one here https://www.4corn.co.uk/archive/diagram ... 0Board.jpg
Shame it's missing detail int the bottom left 🙁
Last edited by guesser on Tue Nov 13, 2018 1:58 am, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

guesser
Posts: 307
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Acorn teletext adapter

Post by guesser » Tue Nov 13, 2018 12:53 pm

I've had a bit of a study of the schematics and have come up with the following possible register details:

Code: Select all

FC10     Status register
FC11     Row register select
FC12     Data register select
FC13     Clear status register

Status register:
  Read
   Bits     Function
   0-3      Link settings
   4        FSYN (Latches high on Field sync)
   5        DEW (Data entry window)
   6        DOR (Latches INT on end of DEW)
   7        INT (latches high on end of DEW)
  
  Write
   Bits     Function
   0-1      Channel select
   2        Teletext Enable
   3        Enable Interrupts
   4        Enable AFC (and mystery links A)
   5        Mystery links B
 
Might still have some missing inverted-ness to some signals, and no idea what the links in the status register are intended for. :)
Last edited by guesser on Tue Nov 13, 2018 6:52 pm, edited 1 time in total.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor
Join the Teletext Discord for teletext chat.

Post Reply