TRS-80 Color Computer
16K TRS-80 Color Computer 1
|Release date||September 1980|
|Introductory price||US$399 (equivalent to $1,238 in 2019)|
|Operating system||Color BASIC 1.0 / 2.0 / OS-9|
|CPU||6809E @ 0.895 / 1.79 MHz|
|Memory||4 / 16 / 32 / 64 / 128 / 512 KB|
|Graphics||MC6847 video display generator|
The RadioShack TRS-80 Color Computer (later marketed as the Tandy Color Computer and sometimes nicknamed the CoCo) is a line of home computers developed and sold by Tandy Corporation. Despite sharing a name with the earlier TRS-80, the Color Computer is a radical departure with its Motorola 6809E processor rather than a Zilog Z80. The Color Computer line is not compatible with software made for the earlier TRS-80.
The Tandy Color Computer line started in 1980 with what is now called the Color Computer 1. It was followed by the Color Computer 2 in 1983, then the Color Computer 3 in 1986. All three models maintain a high level of software and hardware compatibility, with few programs written for an older model being unable to run on the newer ones. The Color Computer 3 was discontinued in 1991.
Tandy Corporation announced the TRS-80 Color Computer in July 1980 to compete with the inexpensive and popular Commodore VIC-20. The Color Computer is a completely different design than the Zilog Z80-based TRS-80 models. BYTE wrote, "The only similarity between [the two computers] is the name".
The TRS-80 Color Computer derives from an "experimental videotext project by the Kentucky Cooperative Extension Service and the University of Kentucky College of Agriculture" in 1977. Motorola Semiconductor, Inc. of Austin, won the contract for the user terminals and Tandy's Computer Division joined later to manufacture the terminals. The initial goal of this project, called "Green Thumb", was to create a low cost Videotex terminal for farmers, ranchers, and others in the agricultural industry. This terminal would connect to a phone line and an ordinary color television and allow the user access to near-real-time information useful to their day-to-day operations on the farm.
Motorola's MC6847 Video Display Generator (VDG) chip was released about the same time as the joint venture started and it has been speculated that the VDG was actually designed for this project. At the core of the prototype "Green Thumb" terminal, the MC6847, along with the MC6809 microprocessor unit (MPU), made the prototype a reality by about 1978. Unfortunately, the prototype contained too many chips to be commercially viable. Motorola solved this problem by integrating all the functions of the many smaller chips into one chip, the MC6883 Synchronous Address Multiplexer (SAM). By that time in late 1979, the new and powerful Motorola MC6809 processor was released. The SAM, VDG, and 6809 were combined and the AgVision terminal was born.
The AgVision terminal was also sold through Radio Shack stores as the VideoTex terminal around 1980. Internal differences, if any, are unclear, as not many AgVision terminals survive to this day.
With its proven design, the VideoTex terminal contains all the basic components for a general-purpose home computer. The internal modem was removed, and I/O ports for cassette storage, serial I/O, and joysticks were provided. An expansion connector was added to the right side of the case for future enhancements and program cartridges ("Program Paks"), and a RAM button (a sticker indicating the amount of installed memory in the machine) covers the hole where the Modem's LED "DATA" indicator had been. On July 31, 1980, Tandy announced the TRS-80 Color Computer. Sharing the same case, keyboard, and layout as the AgVision/VideoTex terminals, at first glance it would be hard to tell the TRS-80 Color Computer from its predecessors.
Tandy viewed businesses as its primary market for computers. Although the company's Ed Juge said in 1981 that the Color Computer was "our entry into the home-computer market", he described it as "for serious professionals", stating that a word processor and spreadsheet would soon be available. In 1987 Tandy CEO John Roach refused to describe it as a home computer. The initial model (catalog number 26-3001) shipped with 4 KB of Dynamic Random Access Memory (DRAM) and an 8 kB Microsoft BASIC interpreter in ROM. Its price was 399 USD. Within a few months, Radio Shack stores across the US and Canada began receiving and selling the new computer.
Color Computer 1 (1980–1983) 
The original version of the Color Computer sports a large silver-gray case with a calculator-like chiclet keyboard and was available with memory sizes of 4K (26-3001), 16K (26-3002), or 32K (26-3003). Versions with at least 16K of memory installed shipped with standard Microsoft Color Basic or (optionally) Extended Color BASIC. The only available connection to a display device is to a TV.
The early versions of the CoCo 1 have a black keyboard surround, the TRS-80 nameplate above the keyboard to the left side, and a RAM badge ("button") affixed on the top and right side of the case. Later versions removed the black keyboard surround and RAM button, and moved the TRS-80 nameplate to the mid-line of the case.
The computer is based on a single printed-circuit board, with all semiconductors manufactured by Motorola including the MC6809E CPU, MC6847 VDG, MC6883 SAM, and RAM, which consists of 2104 (4Kx1) chips (4K models) or 4116 (16Kx1) chips (16K models). The early CoCos only have eight RAM sockets, so upgrading to 32K requires piggybacking two sets of 4116 chips and adding a few jumper wires. A later motherboard revision removed the 4K RAM option and were upgraded to 32K with "half-bad" 4164 DRAMs. These boards have jumpers marked HIGH/LOW to determine which half of the memory chip was good. This was transparent to the BASIC programmer since in either configuration 32K of memory was available. As memory production yields improved and costs went down, many (perhaps most) 32K CoCo 1s were shipped with perfectly good 4164 memory chips; many utilities and programs began to take advantage of the "hidden" 32K.
Users opening the case risked invalidating the warranty. Radio Shack could upgrade all versions that shipped with standard Color BASIC to Extended Color BASIC, developed by Microsoft, for $99. BYTE wrote in 1981 that through Extended Color BASIC, Radio Shack "has released the first truly easy-to-use and inexpensive system that generates full-color graphics". Eventually the 32K memory option was dropped entirely and only 16K or 64K versions were offered.
In late 1982, a version of the Color Computer with a white case, called the TDP System 100, was distributed by RCA and sold through non-Tandy stores. Except for the nameplate and case, it was identical to the Color Computer.
Later, both the Coco and the TDP System 100 shipped with a white case with ventilation slots running the length of the case rather than only the sides. This ventilation scheme was carried over to the CoCo 2. Some late versions of the CoCo have a modified keyboard, often referred to as the "melted" keyboard, with bigger keycaps.
A number of peripherals were available: tape cassette storage, serial printers, a 5.25 inch floppy disk drive, a pen and graphics tablet called the "X-Pad", speech and sound generators, and joysticks.
Color Computer 2 (1983–1986) 
During the initial CoCo 1 production run, much of the discrete support circuitry had been re-engineered into a handful of custom integrated circuits, leaving much of the circuit board area of the CoCo 1 as empty space. To cut production costs, the case was shortened by about 25% and a new, smaller power supply and motherboard were designed. The "melted" keyboard from the white CoCo 1 and the TDP-100 style ventilation slots were carried over. Aside from the new look and the deletion of the 12 volt power supply to the expansion connector, the computer was compatible with the previous generation. The removal of the 12V power supply crippled some peripherals such as the original floppy disk controller, which then needed to be upgraded, installed in a Multi-Pak interface, or supplied with external power.
The CoCo 2 was sold in 16K and 64K models. 16K models use 16Kx1 DRAMs, but the chips are not the common 4116; they are instead 6665 chips (Radio Shack P/N 8040517), which uses only +5V power rather than the triple voltages used by the 4116. 64K models use standard 4164 chips and have a control register at $FFDE/$FFDF to switch between the second 32K of RAM and the OS ROMs. With the ROMs banked out, the entire 64K of system RAM can be accessed.
Upgraded BASIC ROMs add minor features and fix some bugs. A redesigned 5-volt disk controller was introduced with its own new Disk BASIC ROM (v1.1). It adds a new command,
DOS, to auto-boot software from disk (this requires a disk with a special boot sector). This allows the use of software on copy protected disks or third-party operating systems, chiefly OS-9.
Production was partially moved to Korea, with production in the US and Korea happening in parallel using the same part numbers.
Later in the production run,[when?] the "melted" keyboard was replaced with a new, full-travel, typewriter-style keyboard.
The final significant change in the life of the CoCo 2 (models 26-3134B, 26-3136B, and 26-3127B; 16 KB standard, 16 KB extended, and 64 KB extended respectively) was to use the enhanced VDG, the MC6847T1, allowing lowercase characters and changing the text screen border color. These features were not enabled in BASIC. Midway during the production run of these models, the nameplate was changed from "Radio Shack TRS-80 Color Computer 2" to "Tandy Color Computer 2". The red, green, and blue shapes were replaced with red, green, and blue parallelograms.
Creative Computing wrote in December 1984 that the Color Computer was the best educational computer under $1000. The magazine said that it had fewer but better-quality educational software than the Commodore 64, and that Radio Shack was dedicated to the educational market while Commodore was not.
Color Computer 3 (1986–1991) 
By 1985, Color Computer users worried that the company would abandon their computer in favor of the Tandy 1000. Tandy executive Ed Juge stated that year that "No home computer on the market today has the potential horsepower of the Color Computer ... we believe [it] also has a good future".
On July 30, 1986, Tandy announced the Color Computer 3 at the Waldorf-Astoria Hotel in New York City. It came with 128 KB of RAM, which could be upgraded to 512 KB. The panel behind the keyboard and cartridge door plastic were changed from black to grey. The keyboard layout was revised, putting the arrow keys in a diamond configuration and adding CTRL, ALT, F1 and F2 keys. It sold in Radio Shack stores and Tandy Computer Centers for $219.95 (199 CAD in Canada later that year).
The CoCo 3 is compatible with most older software and CoCo 2 peripherals. Taking the place of the graphics and memory hardware in the CoCo 1 and 2 is an application-specific integrated circuit called the GIME (Graphics Interrupt Memory Enhancement) chip. The GIME also provides:
- Output to a composite video monitor or analog RGB monitor, in addition to the CoCo 1 and 2's TV output. This improves the clarity of its output.
- A paged memory management unit breaks up the 6809's 64 KB address space into 8 × 8 KB chunks. The scheme would later allow third party RAM upgrades of up to 2 MB (256 × 8 KB).
- Text display with real lowercase at 32, 40, 64, or 80 characters per line and between 16 and 24 lines per screen.
- Text character attributes, including 8 foreground and 8 background colors, underline, and blink.
- New graphics resolutions of 160, 256, 320 or 640 pixels wide by 192 to 225 lines.
- Up to 16 simultaneous colors from a palette of 64.
Omitted from the GIME are the seldom-used SAM-created Semigraphics 8, 12, and 24 modes. A rumored 256-color mode (detailed in the original Tandy spec for the GIME) has never been found.
Previous versions of the CoCo ROM were licensed from Microsoft, but Tandy could not convince them to provide further BASIC updates. Instead, Microware provided extensions to Extended Color BASIC to support the new display modes. To not violate the spirit of the licensing agreement between Microsoft and Tandy, Microsoft's unmodified BASIC is loaded in the CoCo 3's ROM. Upon startup, the ROM is copied to RAM and patched by Microware's code. The patched code has several bugs, and support for many of the new hardware features is incomplete.
Microware also provided a version of the OS-9 Level 2 operating system shortly after launch. OS-9 uses memory-mapping (so each process has its own memory space up to 64K), windowed display, and a more extensive development environment that includes a copy of BASIC09. C and Pascal compilers were available. Members of the CoCo OS-9 community enhanced OS-9 Level 2 for the CoCo 3 at Tandy's request, but Tandy stopped production of the CoCo 3 before the upgrade was officially released. Most of the improvements made it into NitrOS-9, a major rewrite of OS-9/6809 Level 2 for the CoCo 3 to take advantage of the features and speed of the Hitachi 6309 (if available).
The 6809 in the CoCo 1 and 2 runs at 0.895 MHz; the CoCo 3 runs at that frequency by default, but is software controllable to run at twice that rate; OS-9 takes advantage of that capability.
A popular accessory was a high-resolution joystick adapter designed by CoCo developer Steve Bjork. It increased the resolution of the joystick/mouse interface by a factor of ten at the expense of CPU time. A modified version was included with a MacPaint work-alike Colorware CoCo-Max 3 by Dave Stamp. Combined with a MacWrite-like word processor called MAX-10 (also by Dave Stamp), provided some of the functionality of an Macintosh, but with color graphics and at a fraction of the cost.
The power supply was marginal, and some would overheat if the system memory was expanded to the full 512 KB capacity due to the considerable heat generated by the additional RAM on the optional daughterboard. Some CoCo 3 owners opted to add a small fan inside the case to keep it cool.
Hardware design and integrated circuits
Internally the CoCo 1 and CoCo 2 models are functionally identical. The core of the system is virtually identical to the reference design included in the Motorola MC6883 data sheet and consists of five LSI chips:
- MC6809E Microprocessor Unit (MPU)
- MC6883/SN74LS783/SN74LS785 Synchronous Address Multiplexor (SAM)
- MC6847 Video Display Generator (VDG)
- Two Peripheral Interface Adapters (PIA), either MC6821 or MC6822 chips
The SAM is a multifunction device that performs the following functions:
- Clock generation and synchronization for the 6809E MPU and 6847 VDG
- Up to 64K Dynamic Random Access Memory (DRAM) control and refresh
- Device selection based on MPU memory address to determine if the MPU access is to DRAM, ROM, PIA, etc.
- Duplication of the VDG address counter to "feed" the VDG the data it is expecting
The SAM was designed to replace numerous small LS/TTL chips into one integrated package. Its main purpose is to control the DRAM but, as outlined above, it integrates several other functions as well. It is connected to a crystal at 4 times the television colorburst frequency (14.31818 MHz for NTSC countries). This is divided by 4 internally and is fed to the VDG for its own internal timing (3.579545 MHz for NTSC). The SAM also divides the master clock by 16 (or 8 in certain cases) for the two phase MPU clock; in NTSC this is .89 MHz (or 1.8 MHz if divided by 8).
Switching the SAM into 1.8 MHz operation gives the CPU the time ordinarily used by the VDG and refresh. As such, the display shows garbage; this mode was seldom used. However, an unusual mode available by the SAM is called the Address Dependent mode, where ROM reads (since they do not use the DRAM) occur at 1.8 MHz but regular RAM access occurs at .89 MHz. In effect, since the BASIC interpreter runs from ROM, putting the machine in this mode would nearly double the performance of a BASIC program while maintaining video display and DRAM refresh. Of course, this would throw off the software timing loops and I/O operations would be affected. Despite this, however, the "high speed POKE" was used by many CoCo BASIC programs even though it overclocked the hardware in the CoCo, which was only rated for 1 MHz operation.
The SAM has no connection to the MPU data bus. As such, it is programmed in a curious manner; its 16-bit configuration register is spread across 32 memory addresses (FFC0-FFDF). Writing even bytes sets that register bit to 0, Writing to odd bytes sets it to 1.
Due to limitations in 40 pin packaging, the SAM contains a duplicate of the VDG's internal 12-bit address counter. Normally this counter's settings are set to duplicate the VDG's display mode. However, this is not required and results in the creation of some new display modes not possible when the VDG is used in a system alone. Instead of the VDG requesting data from RAM by itself, the VDG is "fed" data by the SAM's internal copy of the VDG address counter. This process is called "Interleaved Direct Memory Access" (IDMA) by Motorola and ensures that the processor and VDG always have full access to this shared memory resource with no wait states or contention.
There are two versions of the SAM. The early one is labeled MC6883 and/or SN74LS783; the later version is labeled SN74LS785. There are some minor timing differences, but the major difference is the support of an 8-bit refresh counter in the 785 version. This allowed for use of inexpensive 16K by 4-bit and certain 64K by 1-bit DRAMs. Some third-party bank-switching memory upgrades that used 256K DRAMs needed this 8-bit refresh counter to work.
The MC6847 is display generator capable of displaying text and graphics contained within a roughly square display matrix 256 pixels wide by 192 lines high. It can display 9 colors: black, green, yellow, blue, red, buff (almost-but-not-quite white), cyan, magenta, and orange.
The CoCo is physically wired such that its default alphanumeric display is actually "Semigraphics 4" mode.
In alphanumeric mode, each character is a 5 dot wide by 7 dot high character in a box 8 dots wide and 12 lines high. This display mode occupies 512 bytes of memory from $400-$5FF and is a 32 character wide screen with 16 lines. The internal ROM character generator only holds 64 characters, so no lower case characters are provided. Lower case characters were rendered as upper case characters with inverted color. Although simulated screen shots would show this as green on black, on most CoCo generations it was actually green on very dark green.
Semigraphics is a hybrid display mode where alphanumerics and chunky block graphics can be mixed together on the same screen. If the 8th bit of the character is set, it is a semigraphics character. If cleared, it is an alphanumeric. When the 8th bit is set, the next three bits determine the color and last 4 bits determine which "quadrant" of the character box is either the selected color or black. This is the only mode where it is possible (without sneaky tricks) to display all 9 colors on the screen simultaneously. If used to only display semigraphics, the screen becomes a 64×32 nine color graphics mode. The CoCo features several BASIC commands to manage this screen as a low-res graphics display.
The alphanumeric display has two colorsets. The one used by default on the CoCo has black characters on a green background. The alternate has black characters on an orange background. The colorset selection does not affect semigraphics characters. The border in this mode is always black.
The 6847 is capable of a Semigraphics 6 display mode, where two bits select a color and 6 bits determine which 1/6 of the character box is lit. In this mode only 4 colors are possible but the Colorset bit of the VDG can select two different groups of the 4 colors. Due to a peculiarity of its hardware, only two colors are available in graphics blocks when using Semigraphics 6 on the CoCo.
Additional Semigraphics modes
By setting the SAM such that it believes it is displaying a full graphics mode, but leaving the VDG in Alphanumeric/Semigraphics 4 mode, it is possible to subdivide the character box into smaller pieces. This creates the "virtual" modes Semigraphics 8, 12, and 24. In these modes it was possible to mix bits and pieces of different text characters as well as Semigraphics 4 characters. These modes were an interesting curiosity but not widely used, as the Semigraphics 24-screen consumed 6144 bytes of memory. These modes were not implemented on the CoCo 3.
A programmer's reference manual for the CoCo states that due to a fire at Tandy's research lab, the papers relating to the semigraphics modes were shuffled, and so some of the semigraphics modes were never documented. CoCo enthusiasts created experimental programs to try to reverse engineer the modes, and were able to reconstruct the missing documentation.
The bitmap display modes are divided into two categories: resolution and color. In resolution modes, each pixel is addressable as either on or off. There are two colorsets available: black dots on a green background with a green border, and white dots on a black background with a white border. In color modes, each pixel uses two bits to select one of four colors, with the overall colors determined by the colorset: a green border with the colors green, yellow, red, and blue; a white border with the colors white, cyan, magenta, and orange.
Resolution graphics store 8 pixels per byte and are available in 128×64, 128×96, 128×192, and 256×192 modes. Color graphics have 4 pixels per byte and are available in 64×64, 128×64, 128×96, and 128×192. The maximum size of a bitmap screen is 6144.
The 256×192 two color graphics mode uses four colors due to a quirk in the NTSC television system (see composite artifact colors). It is not possible to reliably display 256 dots across the screen due to the limitations of the NTSC signal and the phase relationship between the VDG clock and colorburst frequency.
In the first colorset, where green and black dots are available, alternating columns of green and black are not distinct and appear as a muddy green color. With the white and black colorset, the result is either orange or blue. Reversing the order of the alternating dots gives the opposite color. In effect, this mode becomes a 128×192 4-color graphics mode where black, orange, blue, and white are available (the Apple II creates color graphics by exploiting a similar effect).
Unfortunately, the bit patterns that represent orange and blue can be different each time the system is powered up. Most Color Computer games start with a title screen and ask the user to press the reset button until the colors are correct. This is fixed on the Color Computer 3, and the other color set can be chosen by holding F1 during reset. On a CoCo 3 with an analog RGB monitor, the black and white dot patterns do not artifact.
Lowercase and the 6847T1
The 6847 is capable of using an external character generator. Several third-party add-on boards allow the CoCo to display real lowercase characters.
Late in the CoCo 2 production run, the enhanced 6847T1 VDG was used. It includes a lowercase character generator and the ability to display a green/orange or black border on the text screen. The lowercase capability is disabled by default on these CoCo 2s, and is not mentioned in the manual.
There are two PIA chips in all CoCo models. The PIAs are dedicated mainly to I/O operations such as driving the internal 6-bit Digital-to-analog converter (DAC), reading the status of the DAC's voltage comparator, controlling the relay for the cassette motor, reading the keyboard matrix, controlling the VDG mode control pins, reading and writing to the RS232 serial I/O port, and controlling the internal analog multiplexers.
The earliest CoCo models had two standard 6821 chips. Later, due to changes in the keyboard design, it was found that the 6822 IIA (industrial interface adapter) was better suited to the keyboard's impedance. The 6822 was eventually discontinued by Motorola but was produced for Tandy as an ASIC with a special Tandy part number, SC67331P. Functionally the 6821 and 6822 are identical and one can put a 6821 in place of the 6822 if that part is bad. Some external pull-up resistors may be needed to use a 6821 to replace a 6822 in a CoCo for normal keyboard operation.
Interface to external peripherals
Due to the CoCo's design, the MPU encounters no wait states in normal operation. This means that precise software controlled timing loops are easily implemented. This is important since the CoCo has no specialized hardware for any I/O. All I/O operations, such as cassette reading and writing, serial I/O, scanning the keyboard, and reading the position of the joysticks, must be done entirely in software. This reduces hardware cost but reduces system performance as the MPU is unavailable during these operations.
As an example, the CoCo cassette interface is perhaps one of the fastest available (1500 bits/s) but it does so entirely under software control. While reading or writing a cassette the CoCo has no CPU time free for other tasks. They must wait until an error occurs or all the data needed is read.
CoCo 3 hardware changes
The hardware in the CoCo 1 and CoCo 2 models was functionally the same; the only differences were in packaging and integration of some functions into small ASICs. In the CoCo 3, a new VLSI ASIC called (officially) the Advanced Color Video Chip (ACVC) or (unofficially) the Graphics Interrupt Memory Enhancer (GIME), integrated the functions of the SAM and VDG while enhancing the capabilities of both. The CoCo 3 supports 40 and 80 column text displays and the ability to run at 1.8 MHz without loss of video. The processor was changed to the 68B09E and the PIA was changed to the 68B21, which are 2 MHz parts.
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On October 26, 1990, Tandy announced that the CoCo 3 would be dropped from its computer line.
Wayne Green wrote in 80 Micro in December 1982 that Tandy had "virtually abandoned" the Color Computer. As with its other computers Tandy attempted to monopolize hardware and software sales, but, he wrote, the Color Computer was incompatible with other Tandy software and what was available was of poor quality. "I'm sure there are at least fifty software firms out there that would love to work with the Shack", Green said, but "it seems that the Shack people are at war with their supporters and potential suppliers".
Most current and former CoCo owners agree that Tandy did not take the CoCo seriously, despite it having been their best-selling computer for several years. Tandy failed to market the CoCo as the powerful and useful machine that it was.
Despite Tandy's apparent lack of concern for the CoCo market, there were rumors of a prototype CoCo 4 at Tandy's Fort Worth headquarters. Firsthand accounts came from Mark Siegel of Tandy and Ken Kaplan of Microware. In 2013, a prototype case appeared in the book CoCo: The Colorful History of Tandy's Underdog Computer, but turned out to be a hoax.
A few companies attempted to carry the CoCo torch, but the lack of decent backwards compatibility with the CoCo 3 failed to entice much of the community. Some these systems run OS9/68k, which is similar to OS-9.
Frank Hogg Labs introduced the Tomcat TC-9 in June 1990, which was somewhat compatible with the CoCo 3, but is only able to run OS-9 software. A later version called the TC-70 (running on a Signetics 68070) has strong compatibility with the MM/1, and also runs OS-9/68K.
The Multi-Media One was introduced in July 1990, ran OS-9/68K on a 15 MHz Signetics 68070 processor with 3 MB RAM, and a 640×208 graphics resolution as well as supporting a 640×416 interlaced mode. It includes a SCSI interface, stereo A/D and D/A conversion, an optional MIDI interface, and (later) an optional board to upgrade the CPU to a Motorola 68340 running at up to 25 MHz.
The AT306 (also known as the MM/1B) is a successor to the MM/1 that contains a Motorola 68306 CPU, OS-9/68K 3.0, and is designed to allow the use of ISA bus cards. It was created by Kevin Pease and Carl Kreider, and sold by Carl's company, Kreider Electronics. t was also sold as the "WCP-306" by Bill Wittman of Wittman Computer Products.
- Delmar System IV/Peripheral Technology PT68K-4
Peripheral Technology produced a 16 MHz Motorola 68000 system called a PTK68K-4, which was sold as a kit or a complete motherboard. Delmar sold complete systems based on the PT68K-4 and called the Delmar System IV. The PT68K-4 has the footprint of an IBM PC, so it will fit in a normal PC case, and it has seven 8-bit ISA slots. Video was provided by a standard IBM style monochrome, CGA, EGA, or VGA video card and monitor, but for high-resolution graphics the software only supported certain ET4000 video cards. It appears that most users of this system use/used OS-9, but there are several operating systems for it, including REX (a FLEX-like OS), and SK*DOS. Dan Farnsworth, who wrote REX, also wrote a BASIC interpreter that was fairly compatible to DECB, but it was too little, too late to be of interest to many CoCo users. There was also a card available called an ALT86, which was basically an IBM XT compatible computer on a card, which allowed the user to run MS-DOS programs on it. In fact, both the 68000 and the ALT86 card could be run at the same time, if access to the ISA bus was not needed from the 68000 side of it.
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Gary Becker produced a broadly compatible version of the CoCo3 with enhancements called the CoCo3FPGA. It is a synthesis of the CoCo 3 which is designed to run on the Terasic DE1 FPGA development board. It has currently been ported to the Terasic DE2 and Terasic DE2-115 and may also be ported to other platforms in the future. The CoCo3FPGA contains a 6809 CPU core designed by John Kent which synthesizes the Motorola MC6809. The core has the ability to run at a clock speed of 25 MHz which is considerably faster than the original CoCo 3 which ran at a top speed of 1.79 MHz. All original CoCo 3 graphics modes are supported and additional 256-color modes have been added including a 640x450 x 256-color mode.
- Matchbox CoCo
Roger Taylor is producing a FPGA CoCo 3 based on the DE0-Nano FPGA board.
Clones and cousins
The Dragon 32 and 64 computers are British cousins of the CoCo based on a reference design from Motorola that was produced as an exemplar of the capabilities of the MC6809E (MPU) when coupled with the MC6847 (Video Display Generator - VDG) and the MC6883 (Synchronous Address Multiplexer - SAM). The BIOS code for the Dragon 32 was rewritten based on specifications and API drawn up by Microsoft and, to a certain extent, PA Consulting of Cambridge. The Dragon was a much improved unit with video output in addition to the TV output of the CoCo and CoCo 2. It also featured a Centronics parallel port (not present on any CoCo), an integrated 6551A serial UART (on the Dragon 64), and a higher-quality keyboard. In 1983, a version of the Dragon was licensed for manufacture for the North American market by Tano Corporation of New Orleans, Louisiana. Tano started production at their 48,000-square-foot (4,500 m2) facility in September 83 and were running at capacity just one month later. Unfortunately sales weren't as good as expected and Tano stopped production and support just one year later. A California surplus equipment company, California Digital, bought the remaining stock of Tano built Dragon 64 shortly after and has had new in-the-box Dragon 64s available for purchase as of January 2017.
In Brazil, there existed several CoCo-clones, including the Prológica CP-400 Color and CP400 Color II, the Varixx VC50, the LZ Color64, the Dynacom MX1600, the Codimex CD6809, and the "vaporware" Microdigital TKS800.
In Mexico, the Micro-SEP, a CoCo 2 clone with 64 KB of memory, was introduced by the Secretary of Education. The Micro-SEP was intended to be distributed nationally to all the public schools teaching the 7th to 9th grades. They were presented as a design of the Center of Advanced Research and Studies (CINVESTAV) of the National Polytechnic Institute (IPN). Like the Dragon, these computers also included video output. Whether these computers were "designed" by this institute, or were licensed from the original design, is unclear.
A Taiwan-based company, Sampo, also made a CoCo clone, the Sampo Color Computer. The Sampo was supposedly available in Taiwan, Korea, and possibly other Asian countries. It is believed that Tandy blocked sales in the US with legal action due to copyright infringements on the ROM code.
A cousin of the CoCo, the MC-10, or Micro Color Computer, was sold in Radio Shack stores as an entry-level computer at a lower cost than the CoCo. Released in 1983, it was similar in appearance to the Timex Sinclair models. Like the CoCo, it used the MC6847 VDG and Microsoft Basic, but featured the MC6803 instead of the 6809. The MC-10 lacked such features as an 80 column printer and disk storage system, as well as a "real" keyboard. Accordingly, it did not sell well and was withdrawn after just two years of production. An MC-10 clone, the Sysdata Tcolor, was available in Brazil with 16 KB ROM.
- Ahrens, Tim; Browne, Jack; Scales, Hunter (March 1981). "What's Inside Radio Shack's Color Computer?". BYTE. p. 90. Retrieved 14 June 2014.
- White, Ron (August 1987). "The Tandy Story: It all started 10 years ago in a converted used-car showroom..." 80 Micro. pp. 50–64. Retrieved 2019-05-18.
- Information Technology for Agricultural America (PDF). Washington, D.C.: U.S. Government Printing Office. 1983. p. 327.
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|Wikimedia Commons has media related to TRS-80 Color Computer.|
- CoCo Chronicles, a history of the Color Computer
- CoCopedia, TRS-80 CoCo Wiki
- Color computer technical reference or as a PDF
- Color Computer/OS-9 Forum at Delphiforums
- 1984 Color Computer magazine ad