[Coco] Simple 8-bit VGA Graphics Card

[Gene Heskett]

On Monday 28 January 2013 02:09:58 Kip Koon did opine:
Message additions Copyright Monday 28 January 2013 by Gene Heskett

> Hello My Fellow Cocoers,
> 
> In the course of the development of my 6809 computer, several people
> have suggested that I add a video controller.  Well, I found one that
> looks very interesting and quite simple, only the guy speaks German, so
> if anyone knows German, I’d like to ask that person to translate the
> documentation in the zip files.  The link below is via Goggle
> translator, so I can read the web page with ease.
> 
> http://translate.google.com/translate?sl=de
> <http://translate.google.com/translate?sl=de&tl=en&js=n&prev=_t&hl=en&ie
> =UTF
> -8&layout=2&eotf=1&u=http%3A%2F%2Fwww.ulrichradig.de%2Fhome%2Findex.php
> %2Fcp ld%2F8bit_c_graka>
> &tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.ul
> rich radig.de%2Fhome%2Findex.php%2Fcpld%2F8bit_c_graka
> 
> The following info is from a file in the zip file in German.
> 
> 
> 
> DatenBus Steckerbelegung
> 
> 
> 
> Pin          Funktion
> 
> 1              Daten1
> 
> 2              Daten0
> 
> 3              Daten3
> 
> 4              Daten2
> 
> 5              Daten5
> 
> 6              Daten4
> 
> 7              Daten7
> 
> 8              Daten6
> 
> 9              A1
> 
> 10           A0
> 
> 11           N.C.
> 
> 12           WR
> 
> 13           GND
> 
> 14           VCC (+5V)
> 
> 
> 
> It looks quite straight forward.  So far I figure that the input lines
> to the video card are 8 data bits, 2 address bits, a write bit, ground
> and +5 volts.  Really a very simple interface.
> 
> 
> 
> Another file has the following.
> 
> 
> 
> 8 Bit Grafikkarte für µC
> 
> 
> 
> Garfikkarte hat eine Auflِsung von 256x256Pixel mit 32Farben (6Bit)
> 
> Unterstützt 60Hz mit 32MHz Quarz und 75Hz mit 40Mhz Quarz im
> Auflِsungsmodus 640x480
> 
> 
> 
> Adressen:
> 
> 
> 
> Register 0 = Pixel in horizontaler Richtung (8Bit) Spalte
> 
> Register 1 = Pixel in Verticaler Richtung (8Bit) Zeile
> 
> Register 2 = Farbe (6Bit)
> 
> Register 3 = not use
> 
> 
> 
> Looks like it’s 256 bits x 256 bits x 32 colors using a 6 bit digital to
> analog converter.
> 
> A horizontal frequency of 60Hz with a 32MHZ crystal and 75Hz with a
> 40MHz crystal.  The result is a 640 by 480 VGA screen.

Wrong nomenclature here, 60 or 75 hz is the vertical frequency, but for crt 
style monitors (are there ANY new ones still available today?) the 
important rate is indeed the horizontal because the scan transformer will 
saturate the ferrite core if driven at too slow a rate.  A normal VGA 
monitor, rated for a 31.5 kilohertz H rate, will usually let out all the 
smoke it runs on if driven at a rate below 29 kilohertz.
 
> Register 0 is the horizontal pixel to be accessed.
> 
> Register 1 is the vertical pixel to be accessed.
> 
> Register 2 is the color to be written to the above addressed memory
> location.

I assume as RRGGBB?
 
> The really nice thing about this interface is the custom video
> controller chip which has its own 64KBs of memory.  No need (yet) for
> my computer to have a copy of the video info stored in the computer’s
> main memory, however if I am to merge the graphics commands back into
> Grant’s 6809 Extended Basic, I’ve got my work cut out for me.  J  More
> fun, Yes!  I’m really thinking seriously of implementing this simple
> VGA video controller.

Some of the code to drive that can probably be modeled after the co80 
driver of yesteryear.  Used to drive the WP-RS cards.
 
> I’ll leave the rest for you guys to read on the web site and in the
> downloadable zip file.  I’m sure I’ll come across other video
> controllers and I’m sure you guys have ideas too for a video controller
> of your own for a 6809 8-bit microprocessor based computer system. 
> Have Cocoing & 6809ing!
> 
> Kip
> 


Cheers, Gene
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