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The CoCo's 3rd Time Is A Charm (Part 1)

Greetings retro-fans, and welcome to another month of CoCoLicious! I hope everyone had a great time during the holidays and got to spend some quality time with your families and the retro-machine of your choice. Last month, I finally coughed up the second part of my three-part series about the TRS-80/Tandy Color Computer.

I would like to thank several people at the outset: Nick Marentes, Boisy Pitre, Dennis Bathory-Kitsz, Mark Marlette, and Frank Swygert. Without their generous donation of information and knowledge, this article would've been much shorter and much less informative. As a matter of fact, this article became so big that it had to be cut into two parts. Part two will come out next month, so check back for the conclusion then.

During the production of the Color Computer series, there have been a number of differences, not only in model numbers, but also, board layouts, upgrade paths, and overall design philosophy in some cases. This month should provide a bit of a respite from all of that, but, there’s still quite a bit to go over, so, on with the sho… err article!

Computing In The Mid ‘80’s

There were lots of changes in the computer industry since the 1980 roll-out of the Radio Shack TRS-80 Color Computer (affectionately referred to as the CoCo) by mid-1985. Bill ‘the Incredible Huxtable’ Cosby was pushing the TI-99/4A; Radar O’Reilly and most of the M.A.S.H. cast was mugging for the IBM Personal Computer; Dick Cavet was doing Apple ads; William ‘Capt. Kirk’ Shatner was trying to sell Commodores; Alan Alda broke from the rest of the M.A.S.H. cast and was hawking Atari equipment; and busty spooky chick Elvira was in print selling something called LMBS.

With that much star power, was there anyone left to help sell the Tandy/TRS-80 line? Well, none other than Isaac ‘I, Robot’ Asimov made numerous print ads for the ‘Shack’s computer lines – virtually all of them. Bill ‘The Incredible Hulk’ Bixby made quite a few TV commercials. Celebrities mugging for computer companies weren’t the only changes, either. Apple, Commodore, IBM and Atari all began marketing the first 16/32-bit computers in this time frame as well. Atari had the ST line, Commodore released the Amiga and Apple was making the Macintosh – all based on the Motorola 68000 series.

Some of you may be asking ‘What does this have to do with the CoCo?’ and that would be a legitimate question. While the rest of the computer industry fought amongst themselves with computer models based on the Motorola 68000 series chip, Tandy continued walking their path on three fronts.

First, Tandy invested heavily in the MS-DOS machines with the Tandy 1000 series of computers. With architecture similar to, but not tied to the fate of the PCjr, the 1000 line was a critical and commercial success. There were a number of other lines including the 2000, 3000 & 4000 that helped Tandy remain a computer powerhouse into the ‘90’s.

Second, Tandy continued with the Model III/IV support - even though it was dwindling in sales and software support by this time.

Third, while From 1982 to 1985, several ‘high profile’ magazines stated that the CoCo was dead (it's notable that those publications 'died' long before the CoCo did), Tandy decide to march on with the very successful Color Computer line. Which leads us to...

The Deluxe Color Computer

One very interesting marker on the pathway to the CoCo3 is the Deluxe Color Computer. Several ‘Getting StartedWith Extended Color Basic’ manuals that shipped with the Color Computer 2 line made reference to a Deluxe Color Computer. What made the machine a Deluxe Color Computer? My first knowledge of the machine came last year when a post was made to the CoCo mailing list called 'Remembering the Deluxe Color Computer.' The specs were remembered as being:

  • Double speed mode
  • Real RS-232 port with UART
  • Sound Chip
  • RAM drive
  • New color palette
  • True lowercase video 
  • Accept commands in lowercase
  • 32 or 64k RAM

Evidently, there was a last minute decision to cancel the machine due to cost (more expensive than what Tandy had envisioned for a home computer) and some of it’s parts being used in the CoCo2 as well. According to the post, all of the upgraded/replacement CoCo keyboards Radio Shack was selling at the time came from the Deluxe model pre-production run.

While researching this article, I came across the following information posted on Nick Marentes’ website. In a 1985 issue of The Australian Rainbow, Rob Rosen, owner of Spectrum Projects, had written two articles. One was about the features and cancellation of the Deluxe Color Computer and can be read here: http://members.optusnet.com.au/nickma/ProjectArchive/graphics/256mode/Hind_Sight.jpg.

In the article above, Mr. Rosen mentions the RMS chip – more can be read about this at Nick Marentes’ Project Archive site - which was supposed to add a number of features to either a Deluxe CoCo or even the CoCo3. Since it never went into production, it’s impossible to say which one was supposed to benefit from it. Some of the information on this site will be discussed later as we dig more into the CoCo3’s development. It’s all relevant and important, because it does show that Tandy and Motorola were very interested in providing a more capable machine to customers, but, they realized they needed to do so at an affordable price.

Now, as is par for the course with my articles, when I’m almost done and ready to send, I come across some more information that is pertinent to the discussion. In this case, Nick Marentes sent me some information relevant to the Deluxe CoCo discussion in the form of an interview he had with Mark Siegel, for his book CoCoNuts. For those who do not know, Mr. Siegel is pretty much the father of the Color Computer 3, and claimed to be the CoCo's biggest supporter at Tandy.

Below is an excerpt of the Deluxe Color Computer discussion between Mark Siegel and Nick Marentes. The information below will clarify the questions left unanswered above.

Nick: Do you have any "nightmare" stories to tell of your Color Computer 3 development days?

Mark: My biggest disappointment was the Deluxe Color Computer not coming to market. It was a pretty cool next generation Color Computer 2 but Motorola ran short of video/memory controllers and Tandy had a choice of where to put them and they chose the cheaper Color Computer 2.

(Edited out a section of this response since it didn’t relate to the Deluxe CoCo)

Nick: What were the specifications of the Deluxe Color Computer?

Mark: It had a GI sound chip, a real UART, 64K of memory (in Disk Basic, 32k was used as a RAM drive). It had a 40 column display with a 320x200 mono graphics mode, the Color Computer 3 keyboard and some cool new Disk Basic commands. The OS-9 for it was very nice.

Nick: How was the 40 column display and 320x200 mode generated? The Motorola 6847 video chip used in the Color Computer couldn't produce this.

Mark: My recollection is fuzzy on this but I think we added an additional video controller to the unit. But since it had to go out the RF it was restricted to 40 columns.

Nick: Was it to have a restyled case?

Mark: It was a Color Computer 1 case with some work on the back and it was painted black.

Nick offered the following commentary on the case issue, which does make more sense than painting the case black:

Nick Marentes: I think black was the default color of the moulded plastic and the final production models were to be painted some other color (probably silver again). The original CoCo 1 was actually black when you scraped the silver paint off."

I think it’s safe to say the Deluxe Color Computer could’ve been a very competitive product. It was probably a beneficial decision to cancel the Deluxe model in the long run, since an upgraded model from that could’ve been more costly in the long run. While I’m sure many more great pieces of software would've been made, I doubt we'd have gotten a CoCo3.

Rumors, Rumblings and Ruminations

Now, as early as mid-1985 rumblings of a new CoCo began to hit the street. Lonnie Falk, editor and publisher of the Rainbow Magazine stated as much in an August 1985 editorial (and three more times thru July ’86) discussing some of the new computers hitting the market from the likes of Atari and Commodore. It’s no secret that most of the computer industry didn’t take the CoCo line as a serious competitor. One look at the Chiclet keyboard of the CoCo1 would make most people walk right on by. Many also thought the battleship grey case was hideous looking as well. Few looked into the internals of the machine to see the potential.

At least one CoCo enthusiast shows affection for the Chiclet keyboard:

Nick Marentes: Ironic that the Chiclet keyboard has now become the preferred keyboard seen on all Mac’s and PC laptops. Bring back the REAL keyboard again I say!!

When the white CoCo1 and subsequently the CoCo2 were released, the CoCo got a little more respect. With a smaller footprint, better keyboards, and a better looking case, it indicated to many that Tandy was serious about building an improved CoCo. Below is a link to an internal Tandy R&D document (again, courtesy of Nick Marentes) detailing some of the video features they were trying to provide for an even better Color Computer, http://members.optusnet.com.au/nickma/ProjectArchive/graphics/256mode/gime-r%26d.gif.

Of the specs mentioned, it would appear that most of the above features made it into the CoCo3. However, according to Rob Rosen’s article, the RMS chip did not make it – like the Deluxe CoCo it never went into production.

Nick Marentes: The story I heard is that when Motorola canned the RMS (or couldn’t get it to work reliably), some of the designers left and went to work on the GIME for Tandy. That’s why I suspect, the specs of the RMS is very similar to the GIME. If anything, the GIME is a cut down version of the RMS design. Tandy didn’t do the designing. It was contracted by a chip firm.

If the RMS chip didn't make it, what exactly did Tandy pull out of their hats for the CoCo3?

Enter The GIME

The hardware of the CoCo1 and CoCo2 were identical in functionality; while the hardware changed quite radically over their life spans the two machines were functionally the same. Tandy realized that to compete with some of the newer computers hitting the market, the new Color Computer needed to be able to show off better graphics; the previously shown internal memo reflects that. The new CoCo also needed to be able to address more memory, and if the RMS chip wasn’t to be included to address these issues, something else needed to be.

The Advanced Color Video Chip or more commonly called the Graphics Interrupt Memory Enhancement chip, or GIME, is an ASIC chip that Tandy had developed to handle graphics and memory functions for the new CoCo, bringing the following enhancements:

  • 32x16, 40x24, or 80x24 character text screens
  • 8 foreground and 8 background colors, underline, and blink.
  • Up to 16 simultaneous colors (programming tricks permit more)
  • Palette of 64 colors
  • The GIME provides TV, composite video monitor, or an analog RGB monitor connections

The GIME combined the functions of the 6847 VDG and the 6883 SAM – emulating both chips, providing the above mentioned text screens in addition to all of the graphics modes of the CoCo2, as well as 320x192, 640x192 and 640x225 hi-res graphics screens.

The GIME also provides system timing and device selection, refresh and multiplexing for the RAM, and contains an MMU which allows RAM expansion from 128k to 512k. The new chip did remove all of the semi-graphics modes, as mentioned in the memo.

At the 2005 CoCoFest, a very rare bird was put on display: a CoCo3 prototype board. As you can see, this was NOT a small board; it contained an integrated floppy controller and discrete logic circuitry that would later be condensed into the GIME chip.

CoCo3 Prototype

(CoCo3 prototype shown at the 2005 CoCoFest in Chicago)

Prototype, 1986 & 1987 GIME chips

(Prototype, 1986 & 1987 GIME chip images provided by Nicholas Marentes)

In addition to the GIME, there were a couple of other changes that benefitted the CoCo3. First, the CoCo3’s display was enhanced to provide true lowercase characters at 40 & 80 column widths (really provided by the GIME). Second, the CoCo3 was capable of running at 1.78MHz without loss of display – a problem that plagued some earlier machines. Third, the CPU was changed to the 68B09E and the PIA was upgraded to 68B21 – both which were rated as 2MHz parts. Finally, the CoCo3 got an enhanced keyboard – a full travel, 57 key enhanced keyboard. The additional keys are F1, F2, ALT& CTRL.

One of the biggest benefits of the GIME was that the CoCo3 could not only support 128k RAM, but, there was now a 512k RAM upgrade as well. As you might have guessed, the extra RAM was welcomed by many people including OS-9 users and gamers. I don’t have a full grasp of OS-9 by any stretch; what I do know is it is a multi-user, multi-tasking operating system introduced on the original Color Computer. With the CoCo3, they added windowing capability. This flexibility and power of OS-9 however, is a subject for an upcoming series of articles where I’ll chronicle my learning experience with OS-9/NitrOS-9.

Beyond the above info, not much else is known about the design of the CoCo3’s GIME chip. There is a project regarding the early prototype board shown above, attempting to decode the logic that is suspected to mimic the GIME functions. This is a very important project for CoCo enthusiasts since there are no known replacements for the GIME. If it goes, the CoCo3 is dead.

The CoCo3 Arrives!!!

26-3127 American built CoCo2

Date: July 30th, 1985
Place: Waldorf-Astoria Hotel, New York City
Event: Tandy unleashes the Color Computer 3 on an unsuspecting world.

Well, okay, maybe not unsuspecting, but, most did not anticipate the improvements Tandy gave to the CoCo3. The September 1986 issue of the Rainbow Magazine was full of very positive commentary from CoCo luminaries from Lonnie Falk to Marty Goodman to Steve Bjork on the new hardware. Probably rightly so; below are the official specifications of the Color Computer 3 at launch time:

Display Screen size: 32x16, 40x25, 80x25
Resolution: 320 x 192 (16 colors), 640 x 192 (4 colors), 640 x 225 (2 colors)
Storage : Tape and Floppy
Operating System: Extended Color Basic; Disk Extended Color Basic; OS-9 Level II
First Released: July 1986 
CPU: 8 bit Motorola 68B09E
Clock speed: 2 MHz
Bus type: Tandy Proprietary
Data bus width: 8 bit
Address bus width: 16bit
Memory: 128k expandable to 512k (third party upgrades include 1, 2 & 8 Meg upgrades)
ROM: 32 KB
Interfacing: 1 x Cassette; 1xSerial ; 2 x joystick; 1 x RGB; 1 x RF modulated (TV); 1 x RCA video; 1 RCA Audio; 1 cartridge/expansion slot
Display Screen size: 32x16, 40x25, 80x25
Resolution: 320 x 192 (16 colors), 640 x 192 (4 colors), 640 x 225 (2 colors)
Storage : Tape, floppy and hard disk
Operating System: Color Extended Basic; Disk Extended Basic; OS-9 Level II

The CoCo3 was compatible with almost all CoCo 1 & 2 hardware and software. While the CoCo3 had the same limitations of the CoCo2 regarding the lack of a 12vdc circuit, as long as a multipak interface was used, this was not an issue. Also, if you used an RGB monitor, any software for the CoCo 1 & 2 that relied on artifact colors would be shown only in black & white. There were patches made to correct this in many instances, however, not all software was fixed.

One thing you may notice missing in those specs is a dedicated sound chip. Most computers by the mid-80’s had sound hardware integrated into their design - either available on the motherboard itself or as an add-on card. This is yet another example where CoCo enthusiasts still take Tandy to task. Yes, the 6809 is a very powerful 8-bit CPU. However, it just can’t do all things at once. Having dedicated sound hardware (and sprite hardware for that matter) would’ve made the CoCo 3 a bona fide powerhouse computer. The downside would’ve been the cost. Here’s what Mark Siegel had to say:

Nick: Why wasn't additional sound hardware included in the design?

Mark: I had been given a choice in the production budget that I could put in either a sound chip or a UART. Not enough money for both. So I opted for neither. I put in programmable timers and an interrupt controller. That way I could do both in software.

One immediate difference upon powering up a CoCo3 was the boot screen. It was still the familiar black text on nuclear green, but, the boot message added a line about Microware being involved in the licensing of Microsoft's BASIC interpreter for the CoCo3. Here's the story behind the boot screen:

Nick: Why did Radio Shack elect to use Microware for the 3's enhanced BASIC?

Mark: It wasn't Radio Shack that elected to do that, it was me. Microsoft told Tandy that any new Color Computers had to have its BASIC in it or else!! And that they would not make any changes or supply source code. So I provided Microware with my disassembly of the code and a list of new commands and features and had them do it.

My understanding of what is happening during the boot process is this:

Microsoft's unmodified BASIC interpreter is stored in the CoCo 3's ROM. During boot up, the BASIC code in ROM is copied to RAM which is then patched by Microware's updated code. This is how the additional commands Mark Siegel wanted in DECB 2.1 & Super Extended Color Basic are accessible.

During the first run production, some problems were discovered in what is now known as the 1986 GIME chip. Now, it's a matter of conjecture as to how serious the problem is, or even if it is a problem. Certain code causes sparkly type artifacts on the screen. Some say there's an issue with booting into NitrOS-9 using a machine with the '86 GIME chip. The 40 or 80 column screen tends to cause the computer to hang in the boot process.

Some programmers feel that it's a just a programming issue, others feel that the hardware is not performing as it was intended to. Regardless of personal opinions, the GIME did go thru a redesign for the 1987 models an newer. The newer model CoCo3's do not suffer from the these problems. In my opinion that lends some credence to those who feel it's a hardware problem. Nick Marentes and Mark Siegel discussed these issues as well:

Nick: What about the "sparklies" GIME Chip problem?

Mark: I really don't consider it a problem. The video should be switched on a V-Blank. Many video chips have suffered from this. It's a RAM contention problem and in those days, RAM was slow. After all, the machine did have an MMU.

Nick: What about the horizontal scroll problem? The later GIME corrected this.

Mark: A second run may have been built with faster logic. But we could never really test all the features in the chip so there may have very well been things that didn't work, but were not part of our supported feature set. A lot of programmers used the horizontal scroll including our own demo, I'm not sure that problem you refer to. I'm sure it did not work right in every mode.

Join us next month as we dive deeper into the CoCo 3 and take a look at its Motherboard layout, the differences between the Korean and American CoCo 3’s, as well as what’s been happening with the CoCo 3 since 1990!