TRS-80 Color Computer
The TRS-80 Color Computer, later marketed as the Tandy Color Computer, is a series of home computers developed and sold by Tandy Corporation. Despite sharing a name with the earlier, Z80-based TRS-80, the Color Computer is a different system and a radical departure in design based on the Motorola 6809E and variants of the Motorola 6847 video display generator.
The Tandy Color Computer line, nicknamed CoCo, 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.
All Color Computer models shipped with Color BASIC, an implementation of Microsoft BASIC, in ROM. Variants of the OS-9 multitasking operating system were available from third parties.
History
announced the TRS-80 Color Computer in July 1980 as a low-cost home computer. The Color Computer is a completely different design than the Zilog Z80-based TRS-80 models. BYTE wrote, "The only similarity between 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 of Austin, Texas, 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 chip was released about the time the joint venture started. The 1978 prototype "Green Thumb" terminal used the MC6847 and the Motorola 6809 microprocessor. However, the prototype contained too many chips to be commercially viable. Motorola responded by integrating the functions of many smaller chips into one chip: the MC6883 Synchronous Address Multiplexer. The SAM, VDG, and 6809 were used as the core of the AgVision terminal. It was also sold through Radio Shack stores as the VideoTex terminal around 1980.
The VideoTex terminal provided the foundation 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 ROM cartridges. 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, which shares the same case, keyboard, and layout as the AgVision/VideoTex terminals.
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. The initial model shipped with 4 KB of dynamic random access memory and in ROM. Its price was. Within a few months, Radio Shack stores across the US and Canada began 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, 16K, or 32K. Versions with at least 16K of memory installed shipped with standard Microsoft Color Basic or Extended Color BASIC. The only available connection to a display device is to a TV.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 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 chips or 4116 chips. 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. As memory production yields improved and costs went down, many 32K CoCo 1s shipped with perfectly good 4164 memory chips. 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 is 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 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.
Peripherals included 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 were instead 4517s, which use 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. It adds a new command,
DOS, to auto-boot software from disk. 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.
Around March 1984, Radio Shack began advertising a 64K version of the CoCo 2 which also included an 'enhanced' full-travel, typewriter-style keyboard in the production run, replacing the previous "melted" keyboard.
The final significant change in the life of the CoCo 2 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 titles 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 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 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,,, and keys. It sold in Radio Shack stores and Tandy Computer Centers for $219.95.
The CoCo 3 is compatible with most older software and CoCo 2 peripherals. 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. Taking the place of the graphics and memory hardware in the CoCo 1 and 2 is an application-specific integrated circuit called the GIME 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 chunks. The scheme would later allow third party RAM upgrades of up to 2 MB.
- 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.
- 320x192x4, 320x192x16, 640x192x2, and 640x192x4 from a palette of 64 colors. There are two palette modes - RGB and Composite.
Omitted from the GIME are the seldom-used SAM-created Semigraphics 8, 12, and 24 modes. A rumored 256-color mode 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, 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.