Date   : Wed, 27 Feb 2002 09:18:46 -0000
From   : "Kris Adcock" <krisa@...>
Subject: Re: Circuits involving a SAA5050?

> -----Original Message-----
> From: owner-bbc-micro@...
> [mailto:owner-bbc-micro@...]On Behalf Of Chris Thornley
> Sent: 26 February 2002 18:34
> To: krisa@...; bbc-micro@...
> Subject: RE: [BBC-Micro] Circuits involving a SAA5050?
> Importance: High
>
>
> Hi,
> http://www.qsl.net/zl1vfo/teletext.htm
> As some information on register organisation of the chip etc also BBC
> hardware or Advanced use guide has some information in it.
> Why don't you
> use a dedicate teletext chip and feed data by i2c bus? DO you wish to

Do you know of one? Thats exactly what I need.

> use the device to generate texetxt pages or receive them?

I want to generate a page - but not encoded in teletext, just as a composite
video signal.

>
> Why don't you use Mode 7 on your arc and output the RGB information
> through an encoder into your TV set. I won't be supprise if

The VGA out on the Arc already has a job.

> the chip is
> connected to the CRTC controller chip in the BBC.
>

The /output/ of the 5050 goes through the CRTC. I'm more interested in what
is providing the character bitpattern going /into/ the 5050, as I had always
been under the impression that the characters were stored in the chip
itself.

Reading the SAA 5050 datasheet :

"The basic input to the SAA5050 is the character data from the teletext page
memory. This is a 7 bit code. Each character code defines a dot matrix
pattern."

Now, this seems to mean that the bitpattern for each character is supplied
from elsewhere. Or does it mean that the input 7 bit code (ASCII) is used as
an index into the data containing the dot matrix pattern?

> Chris
>
> -----Original Message-----
> From: owner-bbc-micro@...
> [mailto:owner-bbc-micro@...]
> On Behalf Of Kris Adcock
> Sent: 26 February 2002 10:47
> To: bbc-micro@...
> Subject: RE: [BBC-Micro] Circuits involving a SAA5050?
>
>
>
> > -----Original Message-----
> > From: owner-bbc-micro@...
> > [mailto:owner-bbc-micro@...]On Behalf Of Michael Borcherds
> > Sent: 25 February 2002 19:50
> > To: bbc-micro@...
> > Subject: Re: [BBC-Micro] Circuits involving a SAA5050?
> >
> >
> > > For several years now I've been maintaining a RiscPC system with a
> > teletext
> > > decoder card in it. The card is being used to produce an
> > 80x25 screen of
> > > text as a composite video signal. Now, I need to replace
> > this card, mostly
> > > because the card has a TV tuner in it, and the property
> > where the computer
> > > is based does not have a TV licence. So, I'm looking to
> build my own
>
> > > 'serverely simplified' version of the card. Using an
> > SAA5050 chip seems to
> >
> > Why not rig up a serial/parallel link to a BBC B and use
> its composite
>
> > video output?
> >
> > cheers,
> >
> > Mike
> >
> > (well if you will post to a BBC list :))))
>
> My main reason for posting here was that I figured here would
> reside the
> foremost experts on BBC innards. Yes, I'd thought of using an entire
> Beeb - it's just that that is quite a lot of hardware which I wouldn't
> be using.
>
> Looking at the BBC B circuit diagram again ... I still can't see what
> else is helping the 5050 produce the text. Anyone know?
>
> Cheers,
>
> Kris.
>
>