The Color Computer 3 Prototype

This article was originally printed in the May 2007 Volume 3 Issue 2 of the CoCoNuts! newsletter. See it, with photos, here. See more photos of this prototype here.


  • 2024-03-12 – Corrected resolution of CoCo 3 (incorrectly said 640×480). Thanks, Curtis!

By Allen Huffman

Prologue – In the Beginning

On a warm August day in 1985, a Federal Express delivery truck pulled in to a parking lot in Clive, lowa like it did almost every day. The driver retrieved a nondescript cardboard box from the back of the truck and carried it to the lobby. The box was signed for and left, then the driver returned to his route, unaware of the significance of what he had just been part of. The box, you see, had been sent by Tandy in Ft. Worth, Texas. The recipient was a small computer company called Microware Systems Corporation. The contents of the box were a secret prototype for a new computer which would be appearing the following year in Radio Shack stores nationwide: the Tandy Color Computer 3 (aka, the CoCo 3).

That was two decades ago – a lifetime in the computer world. Few specifics about what went on behind closed doors at Microware or in Tandy Towers are known. What is known, however, is that Microware had previously established a business relationship with Tandy to produce a version of their OS-9 operating system for the original Color Computer. This time, their involvement would go far beyond just doing another port of OS-9 to new hardware. It would involve them working on the onboard firmware to bring the new machine to life. Microware would be expanding Extended Color BASIC to take advantage of the new hardware.

But why Microware? In 1979, Microsoft (yes, that Microsoft) had done the original Color BASIC for the Color Computer so surely they would be the ones to continue doing so. But, by 1985, Microsoft had moved beyond being just a provider of BASIC and those types of projects just weren’t compelling. Some speculate Microsoft would have done it, but it was just cheaper to have another company work on the project. In either case, Microware was likely chosen because they had previous experience working with Tandy and the CoCo on the OS-9 project. Since there were plans to bring out the next generation of OS-9 (Level 2) for the new machine, perhaps the economy of scale (a discount for doing multiple projects) did play a role in this decision. We may never know the full details, but regardless, in 1986 a new CoCo 3 began appearing at Radio Shack stores nationwide, and its new Extended Color BASIC featured enhancements done by Microware.

Although the story of how Microware had to patch and extend Microsoft’s code is an interesting one, this is not that story. Instead, this is the story of the contents of that secret box. This is the story of the CoCo 3 that almost was.

Part 1 – The Discovery

It was January 2005 and the large, three-story custom-built Microware building was finally being vacated by its original owner. Microware had ceased to exist as an independent entity in 2001 after it was acquired by Oregon based RadiSys Corporation. Over the years, the once thriving embedded operating system company had become a much smaller struggling company trying to compete in a market now filled with hundreds of competitors, including offerings from Microsoft and embedded versions of the free Linux. Although the building, completed in 1996, was once fully occupied by Microware staff, it had slowly been rented out as the company reduced in size. At some point, the building was sold and the former owner became a renting tenant. It was on this day that the last remaining Microware folks would be relocating to a much more appropriately sized rented office space a few miles away.

The move was somewhat emotional for those who had been with the company since the 1980s. Efforts were made to preserve any OS-9 related artifacts that might still prove useful, such as motherboards for any versions of OS-9 that were still supported. VME cards were salvaged and server racks were saved, but endless other pieces of ancient hardware were to be recycled. Large trash units had been brought in to the parking lot. Old PCs, SUN workstations, endless cables and old parts were being thrown in to them. A mountain of monitors was stacked high in the lobby, waiting to be picked up by the recycler. Decades of history had been rendered useless by the advances of technology.

One of the final areas to be cleared out was a small storage room in the basement known as “the morgue.” Inside the morgue were some of the more interesting artifacts of Microware’s past. Shelving units full of Compact Disc Interactive (CD-i) development systems stood across from piles of old software disks and tapes. Endless VME I/O cards, motherboards and reference hardware sat under layers of dust next to boxes of blank EPROMS and serial cables. It was a place that, in the 1980s, would have been a hardware hacker’s wet dream, but today it was just a room of ancient technology with no modern value or use to anyone.

Just like Noah and the Ark, two of each potentially useful item was to be saved. Anything that was no longer supported (or functioning) was to be sent to the great recycling center in the sky. Some historic items were allowed to be taken home, including an infamous Japanese video game system that ran OS-9 and featured mechanized 5 1/4″ floppy drives and a fancy joystick. There were a few other pieces of unusual OS-9 hardware that escaped a crushing fate.

For instance, the CD-i machines also had some historic significance. Many were development systems used to create the tools Phillips and other companies used for making CD-i content. Others had been part of a shopping kiosk business known as Micromall, co owned by Microware in the 1990s. These CD-i machines were saved then sold off at the 2006 Chicago CoCoFest, hopefully helping them end up somewhere better than the recycle bin.

During all of this purging, a nondescript brown cardboard box was discovered. One of the remaining long time employees knew of its contents and made sure to set it aside. This box was the same box that Federal Express had delivered twenty years earlier. This box contained not one, but two Color Computer 3 prototypes and a few other surprises. The contents of this box have since helped us learn a bit more about what Tandy had intended the CoCo 3 be.

Part 2 – From Prototype to Pre-Production

Before the discovery of the actual Color Computer 3 prototypes, the CoCo community had already seen what was being called “prototype CoCo 3s.” A few years earlier, some pre-production CoCos were displayed at a CoCoFest convention. The CoCo Communityis official monk, Brother Jeremy, had acquired them somehow. They were the ones used by Microware for developing OS-9 and, we assumed, the Extended Color BASIC extensions. Externally they looked like the CoCo 3s we are all familiar with, but the motherboards inside were different. The GIME chips were earlier prototype versions, different from the ones found in later production units. Little else is known about these machines, but news of their existence spread through the community.

After hearing that “prototype” CoCo 3s had been shown publicly, one of the original Microware CoCo 3 developers made a comment that those couldn’t possibly be the real prototypes because the real ones were still in storage at Microware. This was the first clue that there was something else still to be discovered. Something few had seen, and something hidden away somewhere in a box stored down in a basement.

When the box was opened, it was clear no one had seen or touched its contents for many years, and quite possibly not since 1986. The insides were dusty. The labels were faded and cracked. A small supply of bubble wrap was all that protected the contents. Inside were two large green circuit boards and three smaller ones.

The large boards were covered in chips and wires. The only thing that gave any clue that this was connected to the Color Computer was a series of familiar connectors on the back edge. The standard CoCo joystick, serial and cassette ports were there along with a cartridge connector. Elsewhere on the board could be found a keyboard connector, and further inspection of the chips revealed a few recognizable ones, like a 6809 processor. The amount of chips (on a board four or more times the size of a production CoCo motherboard) was staggering. The back side of the board was covered in dozens and dozens of long green jumper wires.

Two smaller CoCo cartridge boards were also found as well as an unidentified third board that didn’t seem to plug in to anything. The cartridges matched one that had shown up a few years earlier at a CoCoFest that was thought to be some kind of Ethernet networking pak. The third mystery board carried a Copyright 1984 Tandy notice on it, indicating it was probably too early to be anything CoCo 3 specific. It was this set of five boards that was shown at the 2006 Chicago CoCoFest, and this was when the next round of discoveries were made.

CoCo networking cards, and mystery board.

Part 3 – Blue Sky CoCo

“Everything, even the CoCo, starts with a dream.”

When Disney’s Imagineers start designing a new ride or attraction for one of the theme parks, they initially start with what they call the “blue sky” phase. That is, “the sky is the limit.” Anything is possible, even if impossible. These initial concepts and ideas may be far grander than what is technically possibly, or perhaps possible but economically unfeasible. As the project continues, the budget (and often the realities of technology) whittles down the blue sky plans to something much more humble which hopefully will get approved and built. Disney fans know far too well how grand plans originally become much smaller realities, such as how Walt Disney World’s Epcot “Space Pavilion” went from a full experience with a space shuttle launch to a space station, to just a simulator ride that didn’t pretend to be anything grander.

This same approach is common in many areas of design, and likely played a role in the evolution of the Color Computer series. For instance, it is documented that a Deluxe Color Computer was planned but never released. Evidence of this includes references to a deluxe model in the Color Computer 2 manuals. Little is known about the features of this version other than a documented ability to enter BASIC commands in lowercase. Such capabilities never made it in to any official version of Radio Shack CoCo BASIC, but later models did include support for a lowercase display. There were also references to extra keyboard keys. Coincidentally, Radio Shack stores sold some keyboards as spare parts during this time. Theses keyboards had a few extra keys and could be plugged directly in to an existing CoCo. It is believed that these keyboards were designed for the never-produced Deluxe CoCo. Perhaps some day a prototype of this machine will surface.

It is possible that the CoCo 3 grew out of blue sky plans for the Deluxe CoCo, actually allowing more ambitious plans to be made than just minor improvements. All that known for sure today is that the Deluxe CoCo plans got far enough for keyboards to be manufactured and for manuals to be revised and printed.

To understand what was happening, it is helpful to look at what had already happened. Tandy has already evolved the original grey case CoCo several times. There were a few revisions to the original motherboard with the final versions supporting 64K without hardware hacks. A small run of white cased CoCo 1s was also produced which included an updated keyboard. Next was the CoCo 2 in a smaller white case with a similar keyboard, though they were soon revised to have an improved keyboard which would continue to be used on all later models. There were numerous revisions to the CoCo 2 models, though the only significant feature was the addition of true lowercase for the “Tandy” branded units. (None of the models labeled as TRS-80s had this enhanced video chip.) There was also another minor revision that caused the need for Color BASIC 1.3, but the end result was a machine that was effectively no different than the original 1980 model other than in appearance.

To truly make a successor, Tandy needed something bolder than just a new keyboard and case. Game developers wanted to see enhanced graphics. Similar peer systems, such as the Commodore 64, had more colors and hardware sprite capabilities which allowed more advanced games to be created easier. Some of these capabilities were already available as expansion pak add-ons for the CoCo, but developers couldn’t target those enhancements since the base CoCo did not have them. In order to be useful, the hardware would have to be integrated.

Looking at the lineup of add-on hardware paks sold by Radio Shack, certainly building in enhanced audio (like the Speech/Sound Pak) would be useful. The RS-232 pak would also have made a nice addition, effectively giving all those “power user” features to the base model. A “really deluxe” CoCo with better graphics would also need to support something other than an old-style television set. Other obvious enhancements would | include more memory and speed.

Ultimately, the CoCo 3 that was released in 1996 only contained a handful of these blue sky items. Compromises had to be made to keep costs down. One of the original Tandy CoCo 3 developers, Steve Bjork, has stated that there was a requirement for the CoCo 3 to be produced ata lower cost than the CoCo 2 it was replacing. This ambitious economic goal certainly limited all the developer’s requests for enhanced hardware.

When released, the production model CoCo 3 did contain better graphics (up to 640×225 with four colors, or 320×225 with 16 out of 64 colors). More memory was added, with the base model of 128K expandable to 512K. RGB-analog monitor output was added, as well as audio/video outputs for hooking to VCRs or composite monitors. The CoCo 3 could also run at double speed even in RAM mode, allowing a boost in performance for more than just BASIC ROM calls. (The CoCo 1 and 2 had a “double speed” poke which sped up ROM access, but the so-called “triple speed” poke that sped up RAM access garbled the video display. The CoCo 3 allowed the “triple speed” poke to work for both RAM and ROM code without losing the display.)

Other additions were compromises. In lieu of real sound hardware, developers such a Steve Bjork lobbied for and received an enhanced IRQ timer. This didn’t compete with the music chip in the Commodore 64s, but it did allow enhanced background sound effects using the existing CoCo sound capabilities. There was another IRQ that would have dramatically helped with RS-232 performance over the printer/ serial “bit banger” port. It is believed this was meant to substitute for a hardware RS-232 interface, but it was miswired so that potential was never realized. The list of other enhancements that would have been nice but didn’t make it is something discussed to this day, usually under the guise of what would have been ina CoCo 4.

Overall, the CoCo 3 was a significant leap forward for the series. It contained better graphics, more memory, faster usable speed and even added the extra keys that would have been part of the Deluxe CoCo (but still no BASIC enhancements to allow entering commands in lowercase). The new monitor outputs and new color CM-8 monitor allowed using an 80 column screen, finally breaking away from the 1980-vintage 32-column display. It was a significant upgrade and one that developers took too quickly. The new generation of programs, from enhanced games with full color and background sound to the power of OS-9 Level 2, made the new model a more revolutionary a leap than from CoCo 1 to CoCo 2.

This brings us back to that box and the prototype within. By the time hardware is created, even if it’s just a massive circuit board stuffed with chips and wiring, most blue sky goals have been eliminated. The goal of the initial prototype is to begin working on what will hopefully be produced later. Projects certainly continue to evolve, often based on feedback from working with the prototypes, but examining early designs can shed light on the intent of the designers at that moment in time.

As mentioned earlier, the CoCo 3 prototype contained the common ports found on all CoCos up to that point – cassette, joystick, printer, TV RF out, and cartridge. New RCA jacks were added for composite audio/ video output, and a DB9 appeared for the new RGB-analog monitor. While the RCA jacks would make it to the production CoCo 3s, the DB9 connector did not. Instead, an odd square 10-pin header connector was added to the bottom of the machine. This was likely a cost reduction move since placing the connector there on the motherboard probably saved some layout money, and using a surfacemount header was cheaper than adding a DB9 port. Still, it does indicate that Tandy may have intended to use some kind of monitor that had a DB9 connector like other monitors of the day.

On a side note, the production CoCo 3 still contains one mystery related to the monitor port. Under the machine where the monitor plugs in is a square indention that could have fit some kind of small box. Perhaps there was an idea of converting the main RGB-A output to some other format via a converter box (maybe simplifying monitors between US and other parts of the world). Perhaps there was some other intended us that we may never learn about. Perhaps the CoCo 3 prototype will eventually give us a clue. (A more pressing mystery is why CoCo 3 software always asks Composite/TV or RGB? on startup, even though there was a way to detect if a CM-8 was plugged in.)

Something else learned by inspecting the prototype is that Tandy may have had much higher goals for their base model machine. The prototype has no place for RAM expansion. Instead, it is populated with 512K. This would have driven up cost and would have caused real problems during the RAM price crisis of the late 1980s when memory upgrades shot up by hundreds of dollars due to a fire at an overseas production facility. Looking back, releasing a cheaper 128K unit that could be upgraded later was probably a smart move though it ultimately led to few official Radio Shack products taking advantage of systems with that much memory.

Another interesting discovery was noticing a 1773 chip on the prototype. This chip was part of the CoCo floppy drive controller pak. The prototype had the floppy drive circuitry built in and contained a ribbon cable connector for the disk drive. Tandy must have wanted to integrate disk support in the base model, and perhaps had goals of shipping a floppy drive with the system or allowing the CoCo 3 to just plug in an external drive without needing the drive controller. Tandy actually did this very thing with their Tandy 1000 EX and HX PC compatibles. While those systems contained a built-in floppy drive (5 1/4″ and 3.5″ respectively), there was also a port that allowed plugging up an external drive. More on this later.

Probably the most curious observation was that the prototype did not even have a GIME chip. The GIME was a custom IC created to handle things like graphics and memory. In the early prototype stages, before such an expensive chip could be made, designers created the functionality of the GIME using programmable PAL chips and other support hardware. It is unknown how much GIME support is on the prototype, but since Microware used it to create the Extended Color BASIC enhancements (which included the new graphics modes), and since the prototype had 512K, is believed to have implemented the graphics and memory controller that the GIME later would handle.

There could be other secrets in this prototype. Early developers, under Non Disclosure Agreements with Tandy, received pre-production CoCo 3s with pre-production GIME chips. There were two known revisions to the production GIME (86 and 87 revision), and the early development units are believed to have been just earlier (and buggier) versions of what was released. But, documents given to Microware during this project indicated that one of the specifications for the CoCo 3 was a 256-color mode. Steve Bjork has stated that this mode never existed in any manufactured CoCo 3s,

and notes that the graphics hardware itself did not have enough bits available to represent a 256-color map. However, this early prototype may have had the basis for such a mode before it was deemed either too costly or, perhaps, too likely to compete with the Tandy 1000 graphics. The mystery of the specified 256-color mode may finally be unlocked in these early designs.

In a side note, the whole suspicion of a 256-color mode started when a former Tandy Color Computer product manager made reference to it years later. “Has anyone found the 256 color mode?” he asked. No one had, but noted Color Computer programmers John Kowalski

(“SockMaster”) and Australia’s Nick Marentes were able to find abnormalities in the CoCo 3 schematics published by Radio Shack in the Color Computer 3 Technical Service Manual. As Steve Bjork has mentioned, there were not enough address lines for doing an 8-bit color, but the schematics showed some evidence of alterations in that area. There where two extra lines being routed away from the normal path. Perhaps there were plans to achieve the 256-color mode by some way that would allow accessing those extra lines? Nick was able to track down the original designer of the GIME, but he had no recollection of any such mode. It seems likely that this mode, if it ever existed, may not have even made it to the GIME stages.

So the prototype, while not quite a “blue sky” machine with enhanced sound and true RS-232 serial hardware, did certainly represent a somewhat nicer machine than what was actually released. Imagine a CoCo 3 with 512K standard, normal DB9 monitor port on the back, anda place to plug the disk drive ribbon cable in and still have the cartridge port available. This would have removed need for the MultiPak for the large number of CoCoists who used floppy and RS-232, or perhaps floppy and the Speech/Sound Pak.

When the prototypes are fully inspected and, hopefully, reverse engineered, there may be more mysteries discovered. Though the prototypes were supposedly working when they were packed away 20 years ago, until someone qualified has time to inspect them, no attempts are going to be made to power them up.


2 thoughts on “The Color Computer 3 Prototype

  1. L. Curtis Boyle

    Some updates/corrections from your original article:

    We now have 3 Deluxe’s that have been found. Boisy has two of them, but with stock ROM’s (they do have the new hardware – 6551 serial and AY sound chips being the main things). The one that Brian Wieseler now has from Robert Kilgus is the only one know to have an early version of the new Advanced Color BASIC (ultimately it was to be called Deluxe Color BASIC), which included a dozen new commands, RAM drive, device -3 being the new 6551 serial port, a built in terminal program with a subset of VT-52 terminal commands, the T1 true lowercase video chip, a new Option Control register, a special 16K RAM bank area that could map any of the 4 16K banks into a specific spot while leaving the 32K ROM intact, BASIC support for the AY chip, a full screen editor, double speed ROM command (and the rest of BASIC slowed it down when needed – like timing loops, sound, cassette, etc.), lowercase command input, 2 button joystick support with enhanced fire button detection, and more.

    You have the specs for the Coco 3 graphics incorrect – it’s up to 640x225x4, not 640x480x4.


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