Date   : Thu, 09 Sep 1999 11:12:54 +0100
From   : C.J.Thornley@...
Subject: Re: VGA adapter for the BBC micro (FWD)

I have found an article which might help and Ill try to get it scanned in.
Its from an old Ametor radio publication and has a circuit for slow to fast
scan conversion and fast to slow scan coversion perhaps this could be
somehow adapted to handle vga and rgb signal.
For conversion  you need at least 3 ADC sampling at 15.625khz some memory
to store scan lines for each signal and 3 DAC converter to clock the signal
out at 31.5khz. and some latch type circuit to handle the doubling of the
sync.

Chris





"Mark Usher" <marku@...>@... on 08/09/99 22:31:49

Sent by:  owner-bbc-micro@...


To:   <bbc-micro@...>
cc:
Subject:  RE: [BBC-Micro] VGA adapter for the BBC micro (FWD)


>There was an article about this in Mike Cook's excellent
>BODY BUILDING series in the Micro User. This should be online
>so perhaps someone can remind me of the address ...

http://math.mmu.ac.uk/Physics/Acorn/BodyBuild/index.html

Don't get your hopes up to much though. There is an article here that
details how to spilt the combined V + H sync signals.
I did have a look at some of the possibilities and built the above sync
splitter board to make the connection. This worked on a standard CGA
monitor
but not on a VGA monitor.

I then used a sync doubler to double up the frequency from 15.625 (CGA) to
31.5 (VGA). This was a circuit that Chris Thornley put me onto, and was
originally intended for the Amiga. I had a stable picture, but
unfortunately
it was "ghosted" 3 times across the screen.

IIRC the amiga has the same output levels as the Beeb and there are quite a
few docs and circuits around on the net that detail how to make this
conversion. Just do a search via Alta Vista for "amiga" and "VGA" etc. You
will find something.

Let us all know how you get on. I am still sure it is possible for this to
work, it just requires someone with a little more than my basic knowledge.

Mark