How to Build a “CoCo 4”

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Terasic DE0-Nano FPGA board

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  Although some ROMs and software may be out of date and the author may not give a hoot who’s doing what with it, this is not a Tandy or Radio Shack product and we will not be suggesting in any way that it is.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 daughter board for Terasic DE0-Nano. Runs OS-9 and NitrOS-9 like a boss!

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 the CoCo community.  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 pre purchased and added to my stock pile. 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.  When you see the Digi-Key parts list below you’ll know that We’re Safe.

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.



  1. Terasic DE0-Nano FPGA board (Terasic) (Digi-Key)
  2. NanoMate upper daughter board for the DE0-Nano’s upper 2 headers.
  3. Coming soon – lower analog/joystick daughter board for the DE0-Nano’s bottom 2×13 header.
  4. PS/2 keyboard and mouse
  5. VGA monitor or VGA-capable TV
  6. 1/8″ male to male stereo audio cable for amp or TV input
  7. 2 GB SD card with CoCo archives provided on this site soon
  8. You’ll want a nice 3-D printed case which I’m sure somebody in the CoCo community will develop very soon.  That person needs to contact me to see if they qualify for a free system to work with in exchange for their guarantee to offer near perfect cases to the community for a cost, of course.
  9. That’s basically it!  All other hardware is burned to the FPGA chip, and let me tell you — it holds a LOT of CoCo hardware gadgets.

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.


NanoMate Rev.3/4 Assembly Guide
You MUST REMOVE the DE0-Nano's top plastic dust cover and 4 SCREWS before installing the NanoMate daughter board!
nanomate_diagram  rev4
R1 ........... 82 Ohm resistor for VGA HSYNC
R2 ........... 82 Ohm resistor for VGA VSYNC
R3,R6,R9 ..... 390 Ohm resistor for VGA Red0,Green0,Blue0
R4,R7,R10 .... 820 Ohm resistor for VGA Red1,Green1,Blue1
R5,R8,R11 .... 1.8K Ohm resistor for VGA Red2,Green2,Blue2
R12-R19 ...... 10 KOhm resistor for PS/2 level conversion
R20 .......... 820 Ohm resistor for front panel LED
C1,C2,C3 ..... .1 uF (104) ceramic capacitor for decoupling
C4 ........... 47 uF 25V electrolytic capacitors for WIFI module decouple
Q1-Q4 ........ 2N7000 N-channel MOFSET transistor for PS/2 level conversion. 

Other components are either obvious or marked with the part # on the board.
The only difference in the rev.3 and rev.4 board is the rotation of the WIFI module header. 
For the rev.3 board, the WIFI module must extend away from the board.
For the rev.4 board, the WIFI module faces in the direction of the arrow next to the header.

DIGI-KEY Preloaded Shopping Carts!
Please note that you’ll need to compare your FINAL ORDER with the Bill Of Materials below to determine what REMAINING parts you need to buy from places like Amazon, Ebay, Jameco, or another electronics supplier.

I live in the USA and I need as many parts as possible FOR 1 SYSTEM, without the DE0-Nano.

I live in the USA and I need as many parts as possible FOR 1 SYSTEM, with the DE0-Nano.

I live in the USA and I need as many parts as possible FOR 3 SYSTEMS, without the DE0-Nanos.

I live in the USA and I need as many parts as possible FOR 3 SYSTEMS, with the DE0-Nanos.

Why would you need the parts for *3* systems??  Because the NanoMate PCB supplier (OSH Park) only sells in multiples of 3 boards, and it is cost effective to do the same for the components and either send kits or fully assembled units to other people.

If you prefer to build your own shopping cart, use the following list as a guideline.  You may also remove or adjust the quantity of items for the above automatic shopping carts after you are on the Digi-Key web site. The remaining few board components can be found all day long on ebay and Amazon.



CoCo 3 clone system (subject to slight changes not affecting overall design)

(1) Terasic DE0-Nano FPGA board (Terasic) (Digi-Key)
(1) NanoMate upgrade board for the DE0-Nano (OSH Park, minimum 3 boards)

(2) – 2×20 straight male header (is keyed) for connecting NanoMate to DE0-Nano (Digi-Key S9200-ND)
(3) – 390 ohm, 5%, VGA lower bits
(3) – 820 ohm, 5%, VGA middle bits
(1) – 820 ohm or near for 3.3V front panel green LED
(3) – 1.8K ohm, 5%, VGA upper bits
(2) – 82 ohm – VGA HSYNC, VGA VSYNC
(8) – 10K ohm – for PS/2 bi-directional level shifters
(4) – 2N7000 transistor, for PS/2 bi-directional level shifters (Digi-Key 2N7000TACT-ND)
(3) – 0.1uF decoupling capacitors for SRAM and MCP4822 DAC
(1) – 2×4 straight male header for ESP8266-01 Wifi module (Digi-Key S7107-ND)
(1) – 1×6 right-angle male header for HC-05 or HC-06 bluetooth module (Digi-Key S5481-ND)
(1) – 2×8 straight male header for SD card module (Digi-Key S7076-ND)
(2) – AS6C4008-55PCN 512KB SRAM (Digi-Key 1450-1027-ND)
(2) – 32-pin sockets for SRAM (highly recommended!) (Digi-Key ED3053-5-ND)
(1) – VGA jack (Digi-Key A35116-ND)
(1) – audio jack (Digi-Key CP-43514-ND)
(2) – PS/2 jacks (Digi-Key CP-4060-ND) (Amazon, ebay, Amazon) (Has common/popular pinout; some connectors may need their anchors straightened using pliers due to the very tight fit on some NanoMate boards.  However, the snug fixture will reduce or eliminate issues resulting from plugging in PS/2 devices frequently.)
(1) – 5mm 3.3v green LED for front panel (Digi-Key 350-1598-ND)
(1) – MCP4822 stereo audio DAC (12-bit), but 4812 and 4802 will also work. (Digi-Key MCP4822-E/P-ND)
(1) – 8-pin socket for audio DAC (Digi-Key AE9986-ND
(1) – SD card module ($2.84 USA Ebay Seller, free shipping)
(1) – TSOP4838 infrared receiver (Digi-Key TSOP4838-ND)
(1) – ESP8266-01 WIFI Module (Amazon USA Seller, Amazon, ebay)
(1) – 47 uF decoupling capacitor for WIFI module (Digi-Key P5137-ND)
(1) – optional HC-05 bluetooth module (Amazon)
(1) – 2GB SD memory card.  Software needed to program or manage the disk images on the card (CoCoPak.exe, Win32 Disk Imager)

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 a NanoMate upgrade board? From OSH Park and me (links to order will be provided SOON).

Where can I get most or all of the other 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 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 brand new Terasic DE0-Nano for lab work).
  • Allen Huffman, Steve Batson, Scott Brooker, numerous others (initial kick start donations).





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