How to Build a “CoCo 4”

>>> Download Support Files Here <<<


The following article is “live” and will change frequently, so please bookmark this page and return often for important DETAILS and CHANGES that may affect the assembly and use of your system.

Are you ready to own an affordable CoCo 3 clone with extra features?

  • Employs Greg Miller’s new cycle-perfect 6809 core with .89, 1.79, 3.58, 7.16 Mhz rates.
  • The most accurate and realistic Tandy Color Computer 3 clone available. Runs OS-9/NitrOS-9 like a boss.
  • 1MB of RAM.
  • VGA port, 512 colors, up to 640×480 resolution, double the width and height of any graphics/text mode. Enjoy up to 80×60 full color text.
  • SD card virtual disks/drives are also mapped to the FDC for high compatibility with floppy-based software.
  • Smart hi-res joystick/mouse circuit lets you run ColorMax Deluxe, CoCoMax III, gshell, etc. using your PS/2 mouse without having to toggle any switches.
  • HQ stereo sound jack for all audio generated by the system, 8 to 12 bits of precision per speaker.
  • Halt / no-halt GPU draws super fast lines, boxes, filled boxes, memory copies and memory fills.
  • WIFI and bluetooth serial capable. CoCoNet bluetooth disk drives from DOS or OS-9.

First, let me say that this new system isn’t “box ready” at this point nor will it be sold as a product mainly due to copyright issues with ROMs and included software, etc.  Although some ROMs and software may be out of date and the author may not give a hoot who’s doing what with it, this is not a Tandy or Radio Shack product and we will not be suggesting in any way that it is.  There will be no Tandy or Radio Shack labels on this new CoCo hardware and there is no affiliation with any corporation whatsoever.  You might ask, what about ROM paks and my Speech/Sound cartridge, hard drive controller, etc?  No cartridges are used or required.  For example, the MicroSD Drive Pak, floppy disk controller, Orchestra-90CC, etc. are built into this system.  Need I say more? This will be an all-in-one solution to the best of my ability, and if I may say so, the idea is going Very Well.

By the way, this FPGA-based CoCo system uses what some people call an “FPGA development kit” with one giant “gotcha” catch…  the DE0-Nano FPGA kit is just a small board with headers with a plastic dust cover mounted to the top which when easily removed using 4 screws takes away the whole “kit” look.  Really, you’d be hard pressed to spend money developing anything close to the power of this small board that can work in harmony with a daughter board to do almost anything imaginable with digital signals. So, this system is far from being the fpgacoco3 project which requires a large and more expensive DE1 FPGA *Kit* and an analog board and possibly even an SRAM replacement (Scooby Doo says ughhh?)  but ours is just as powerful, so… please read on!

NanoMate awesome daughter board for Terasic DE0-Nano

To get up to speed on this new CoCo before you decide to build one or buy a pre-assembled kit from somebody in the CoCo community, first visit the CoCo On A Chip facebook group to see actual videos and discussions about this CoCo that was started on July 4, 2015. This thing just didn’t happen out of thin air.  Family vacations were sacrificed and much soul has been put into this thing on a daily basis.

No, this CoCo model is not “smoke and mirrors” and it’s certainly not vapor ware or vapor hardware but more importantly much thought has been put into how this computer will be adopted by people in the CoCo community who want an alternative system for whatever reason they need.  Components have been chosen based on the endless supply of them so that no component will just suddenly “vanish” from the web after somebody does a huge buy-in, etc.  Any component that “dries up” suddenly like the 4D Systems uDrive module did or the EB301 bluetooth that were used in past products of mine have been secured. If something truly dries up and can’t be found (not a chance) I will simply release a new PCB that fits another brand of the required component such as SRAM, PS/2 connectors, audio jack, and VGA jack, etc.

As I said, this page is a work in progress and you’ll want to make sure you have the latest information about components, SD card updates, tutorials, and other happenings with this project and I’ll try to provide the links to everything you need in one place.

I also want to re-introduce myself.  My name is Roger Taylor and I was studying digital logic and circuits as far back as 12 years old and was writing programs in notebooks before I even owned my first home computer.  Some know me as a software guy.  None know me as a hardware guy.  Always keep’em guessing, right?  Right.  You might even say that this new CoCo clone sort of created itself.  It knew it had to be so the original flashing LEDs of a simple 6809 CPU with 4K of RAM and no video or anything else, uh, reached out to me and said: I need more gates.  Give me video or give me death.  Hey man, 1MB, please?  About, oh, 2 years later, the system has evolved into a full CoCo 3 clone that runs OS-9 like a boss and even runs Sock Master’s demos like a champ.  This project has been very fun yet extremely demanding.  I’ve put all of my knowledge of digital design and programming into this system and I’m still learning new things as I go.  That’s also important!  Always keep learning.  Never let others discourage you on something you love doing.  Just do it and knock their socks off.



  1. Terasic DE0-Nano FPGA board (Terasic) (Digi-Key)
  2. NanoMate upper daughter board for the DE0-Nano
  3. NanoLog lower daughter board for the DE0-Nano
  4. 3-D printed case by John Strong
  5. PS/2 keyboard
  6. PS/2 mouse (if you don’t have a real CoCo joystick)
  7. VGA monitor or VGA-capable TV
  8. 1/8″ male to male stereo audio cable for amp or TV input
  9. FAT32 SD card with your favorite CoCo .dsk images and OS-9 images.


You’ll also need to grab some support files and also program your DE0-Nano board!

Either you or somebody else will have to program your DE0-Nano board once or each time an upgrade to the CoCo system is released online.  To program the Nano yourself, you’ll need a free copy of the free Quartus II 15.0 software and a Windows PC with a USB port.  Links to people who can provide a pre-programmed DE0-Nano or program yours for you will be provided over time on this site or you can ask around in the Color Computer facebook group.


What does the Terasic DE0-Nano do? It has chip real estate space that we will program to become a 6809 CPU, GIME, 6821 PIA, 6551 ACIA, AY-3-8910, and much more!

Where can I get a Terasic DE0-Nano? From the Terasic web site, Amazon, ebay, and many other sellers, with Terasic being the cheapest source for a brand new unit.

What does the NanoMate board do? It adds VGA, SRAM, PS/2, audio, WIFI, Bluetooth, SD card to the DE0-Nano!

Where can I get most or all of the required components for the NanoMate board? Jameco, Digikey, are just a few places you can round up many of these items in one shipment.  Amazon and ebay are great places to find many of the optional and Arduino type components for cheap!


The following people and others have contributed significant information or resources to this project:

  • Bill Nobel (NitrOS-9 enhancements: 80×28, 80×30, 80×48, 80×50, 80×56, and an awesome 80×60 text mode, 7 Mhz CPU, and more).
  • Erik Gavriluk (donated an extra new Terasic DE0-Nano for lab work).
  • Greg Miller (cycle-accurate 6809 CPU core, first of it’s kind!)
  • Allen Huffman, Steve Batson (donations).
  • Scott Brooker (has donated the most $ allowing free systems to be built for numerous key developers).





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