Date : Mon, 08 Jun 2009 00:48:46 +0100
From : bbcmailinglist@... (Ian Wolstenholme)
Subject: Teletext Display Error
I've just written a very quick BASIC routine to load a saved page into
RAM and display it in screen memory, changing &80 to &84 as it goes
along. I'm sure with a bit more time I could do something which traps
the OSWRCH vector or whatever it is and replaces the black with blue
for correct display of pages through the Adapter.
Sailing By is just coming on...must be bedtime!
Best wishes,
Ian
----- Original Message -----
From: Rob [mailto:robert@...]
To: bbcmailinglist@...
Cc: bbc-micro@...
Sent: Mon, 8 Jun 2009 00:28:12 +0100
Subject: Re: [BBC-Micro] 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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