Date   : Mon, 08 Jun 2009 00:28:12 +0100
From   : robert@... (Rob)
Subject: Teletext Display Error

2009/6/8 Ian Wolstenholme <bbcmailinglist@...>:
> The text is "there", if I overtype the control codes at the beginning of
> the line then the text appears. ?I haven't got a Teletext TV tuned to
> analogue at the moment either, but it looks likely that it is black text which
> isn't displaying.

It's quite likely...  That's the trouble with people creating pages on
"modern" kit  they forget that the older equipment might not be able
to display it.

>
> Can the Beeb be made to generate black text in Teletext mode, or this
> something I'm just going to have to live with?

As far as I know ... No it can't.  The closest you'll be able to do is
to change it to Blue..

I'm a little rusty at the moment to do it quickly, or I'd throw some
code together, but it'd not be a big job to throw some 6502 code to
scan the mode 7 screen memory and swap &80 to &84.  Link that into the
refesh vector and it'll be completely transparent..  If you want to be
clever, you could track the background colour to avoid blue-on-blue..

(Now that reminds me of a viewdata terminal I wrote for a client once
.. I created the display that way, copying it from a seperate buffer
in the refresh.  It was the only viewdata terminal I knew of that
coped with the overwriting of a double-height code correctly!)

Rob

>
> Best wishes,
>
>
>
> Ian
>
> ----- Original Message -----
> From: Rob [mailto:robert@...]
> To: bbcmailinglist@...
> Cc: bbc-micro@...
> Sent: Sun, 7 Jun 2009 22:21:21 +0100
> Subject: Re: [BBC-Micro] Teletext Display Error
>
> Hmm....
>
> I haven't got a TV that's actually tuned into the analogue broadcasts
> to check, but it's possible that that are using Black Text ..
> Logically this would be CHR$(128) bt the SAA5050, like most chipsets
> of it's era, doesn't support it,
>
> If you save a page, then *DUMP it, see if the text is there, preceeded
> with an &80.
>
> Rob
>
> 2009/6/7 Ian Wolstenholme <bbcmailinglist@...>:
>> I've noticed a problem with certain Teletext pages being displayed
>> incorrectly via the Teletext adapter.
>>
>> Actually, I have been aware of this problem for several years but I put
>> it down to bad tuning on my Acorn Teletext adapter, but now I've noticed
>> the same problem using the Morley Teletext adapter on a different aerial.
>>
>> It occurs on lines where there is a coloured background, and the text
>> colour does not display, leaving a "blank" line of colour.
>>
>> If anyone is still using Teletext and can go to page 704 on BBC-1, this
>> is an index of the local government results between pages 707 and 712.
>> On my Teletext adapters, the two lines for page 707 are blank, the first
>> line is white and the second line is yellow. ?The second line for page
>> 709 and the first line for page 710 are both white.
>>
>> (I can probably take some pictures to illustrate if it will help.)
>>
>> Is there a way to cure this problem?
>>
>> Best wishes,
>>
>>
>>
>> Ian
>>
>>
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>>
>>
>
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