[Coco] Simple 8-bit VGA Graphics Card

[Kip Koon]

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.ulrich
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 Auflösung von 256x256Pixel mit 32Farben (6Bit)

Unterstützt 60Hz mit 32MHz Quarz und 75Hz mit 40Mhz Quarz im Auflösungsmodus
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.  

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.

 

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.

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