ISA CGA

Color Graphics Adapter - Redux

Introduction

The Color Graphics Adapter (CGA) Redux board is a more or less faithful clone of the original IBM CGA, based on the original schematics.

Since revision 0.2 of this board, You can decide to build it with the "new" or "old" style composite output, giving you slightly different colours.

Have a look HERE for a blog post that discusses the difference in regard to the famous 8088MPH demo!

Disclaimer

I take NO responsibility for what happens if you decide to build and use this card. Your computer might crash, catch fire or be destroyed in other nasty ways. You're encourauged to take what you deem fit from this, and use it in your projects!

Functionalities

✅ means I tested the functionality and it works, ❌ means I tested the functionality and found issues, ? means that the functionality has yet to be tested.

• [✅] Digital display in text mode, 40 columns
• [✅] Digital display in text mode, 80 columns
• [✅] Composite display in text mode, 40 columns
• [✅] Composite display in text mode, 80 columns
• [✅] Graphics mode in digital
• [✅] Graphics mode in composite
• [✅] Run CheckIt video test
• [✅] 8088MPH Demo
• [?] Light pen input

Bill of Materials

Character ROM

This board needs a character ROM to work. I would advise to search for a dump of IBM P/N 5788005, concatenate it four times and burn it on a 27C256 EPROM.

Component substitutions

• U4,U5 and U101 should all be 'S174s, but I had only 'LS174 available. The board looks to be working without issues anyway
• U50-U57 are all 120ns DRAMs in my original board. I had only 150ns chips for this build, and they worked fine
• U9,U10 are 74153 chips. I tried to replace them with 74LS153 chips by Texas Instruments with good results. Needs some testing with colored screens
• U50-U57 can be substituted by 41256 / 4164 DRAMs like the M5K4164 or HM4864P (the additional address lines are grounded). Tested with HM4864P

Support

If you wish to support me in building new hardware and software for old machines, throw a few euros in my direction via Ko-Fi ☕!

💰 Selling these boards 💰

I you want to contact me about selling this project, you can reach me via email at 0hkzUNDERSCOREprojects6ATposteoDOTnet after properly fixing the email address by removing the digits and replacing the uppercase words with the proper characters.

Contacts via other channels will be ignored, as it means you did not read this document thoroughly.

"Collaborations" will boil down to the following:

• If you wish to produce and share this project at a loss or at cost, go for it. I am only asking for attribution and to let me know via email.
• If you want to do it for profit, let's discuss it. I'll probably settle for a rough 5% of the profit. Importing components is getting more expensive by the day, so this will contribute to me making future projects available for free.
• I will NOT do customer assistance for you or your customers. This is a hobby, not my job.

If this is not ok for you, you're cordially invited to go bother someone else :)

Authorized sellers will be listed in this README. If you find someone selling my boards without being listed here, it means they're stealing other people's work.

Known issues

Rev 0

• The Composite video out has an inverted connection for that type of footprint. (fixed in rev 0.1)
• Silkscreen for U28 says 74LS10, but it's actually an 74S10 on an original board (fixed in rev 0.1)
• traces that connect the edge to the power planes for 5V and GND are a bit too thin for my taste (fixed in rev 0.1)

TODO

• ???

Credits

Thanks to Sergey Kiselev for his symbol/footprint library!