Finally on HaD after more than a year! And finally working!

A project log for uPD7220 Retro Graphics Card (and VGA hack)

Making an 80s GDC run for the first time in decades, and my first real hack on

Dylan BrophyDylan Brophy 04/04/2019 at 06:290 Comments

Over a year ago I wanted a graphics card for my Z80 computer.  I made a prototype with the uPD7220, but I never got it working.  Until...

As it turned out, I made TONS on mistakes in the original design.  There are issues with the new design too, but it works well enough (after a hack, more on that later). Anyway, after playing with the first prototype and trying various hacks, I ended up with a valid VGA signal!

I don't think the uPD7220 was ever supposed to output VGA, considering VGA was introduced about four years after the uPD was, so it's awesome that it can output a VGA signal.

After studying the uPD datasheet and my schematic in depth, I eventually found most of the problems and ended up with my second prototype (which I am using now).  I've managed to get it to do the basic things I need it to do.  Getting from basic initialization to drawing pixels was very difficult, especially with such a complex device and no example code/libraries, but it was definately worth it.  I now want to share what I've learned about it so that more people can use this GDC (GDC = Graphic Display Controller).

I plan on adding more and more information to this project so others can use my work as a reference.  I also am going to create a Z80 driver, which I will post here as well.