Date   : Tue, 16 Jun 2009 15:41:59 +0100
From   : jumbos.bazzar@... (Mark Haysman)
Subject: 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
>