Date : Tue, 16 Jun 2009 17:46:19 +0100
From : philb@... (Phil Blundell)
Subject: Black Teletext
You could also try patching the teletext ROM to replace &80 with &84 at
the point where it draws to the screen. I imagine it should be fairly
easy to locate the code in question, and there are probably a few spare
bytes where you could store an extra subroutine.
p.
On Tue, 2009-06-16 at 17:25 +0100, Ian Wolstenholme wrote:
> Oo err, all a bit beyond me, daughter boards and all, but the VSync event
> might be a goer. I suspect it would be a bit much to check all 1024 locations
> on a VSync event, but perhaps I could check a quarter of the screen every
> 50 VSyncs, something like that. There would be a bit of a delay in updating,
> but it wouldn't matter too much for my purposes.
>
> Best wishes,
>
>
>
> Ian
>
> ----- Original Message -----
> From: Mark Haysman [mailto:jumbos.bazzar@...]
> To: bbc-micro@...
> Sent: Tue, 16 Jun 2009 15:41:59 +0100
> Subject: Re: [BBC-Micro] Black Teletext
>
> Hi.
>
> I don't think so in software. Not quite sure why, but the SAA5050 doesn't
> get supplied with a regular D7, it seems to come from DEN of the 6845. That
> and D6 seem to go off via some logic to Pin 10.
>
> Thinking logically, I'd try replacing the 74LS273 at IC15 with a GAL (You'd
> need a daughterboad to get the pins in the right places) that looked for
> &80, and set D2 high regardless of D2s state:
>
> d2 = d2
> # d7 & !d6 & !d5 & !d4 & !d3 & !d1 & !d0 & en
> d2.clk = clk
> d2.oe = ttxvdu
>
> That would also give you an enable pin, "en", when set high, does the
> modification, when low it's normal. The rest of the pins would be simply
>
> d0 = d0
> d0.clk = clk
> d0.oe = ttxvdu
> ....etc
>
> ...I think! I've not tested this, just thought of it now, so don't curse me
> if it doesn't work, or if it's totally the wrong way of doing it!
>
> Mark.
>
> ----- Original Message -----
> From: "Ian Wolstenholme" <bbcmailinglist@...>
> To: <bbc-micro@...>
> Sent: Tuesday, June 16, 2009 2:31 PM
> Subject: [BBC-Micro] Black Teletext
>
>
> At the weekend I wrote a little routine which traps the OSWRCH thingy
> and changes any VDU code &80 into an &84. Much to my surprise, it worked!
> So if I typed VDU &80,65 I would get a blue letter A etc.
>
> Except it doesn't work for the Teletext adapter, which must load the pages
> direct into screen RAM!
>
> Is there a way to trap any write to the Mode 7 screen RAM and do a similar
> fiddle?
>
> Best wishes,
>
>
> Ian
>
>
>
>
> --------------------------------------------------------------------------------
>
>
> > _______________________________________________
> > bbc-micro mailing list
> > bbc-micro@...
> > http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro
> >
>
>
>
> _______________________________________________
> bbc-micro mailing list
> bbc-micro@...
> http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro
>
> _______________________________________________
> bbc-micro mailing list
> bbc-micro@...
> http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro