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Color Computer 3

From CoCopedia - The Tandy/Radio Shack Color Computer Wiki
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More model specific info and pics can be found here: Color Computer 3


The Color Computer 3 (catalog # 26-3334) debuted on July 30, 1986, 6 years and 1 day after the debut of the original TRS-80 Color Computer. It featured an improved keyboard with standard PC style keys and four additional keys (F1, F2, CTRL, ALT) and a whopping 128K for $219.95. It was expandable up to 512K for an additioanl $149.95 (26-3335). This required a plug-in daughter board and the removal of the four 128K RAM chips. The circuit board was smaller than previous models and was more highly integrated. The SAM chip was replaced by a new integrated video/memory management chip, the GIME (Graphics Interrupt Memory Enhancer). A 2 MHz 68B09E replaced the standard 1 MHz 6809E. Since the CoCo derives its clock from the video clock crystal, the CoCo3 didn't run at a full 2 MHz, but at 1.79MHz, twice the original CoCo clock rate. On power up it only runs at the original clock rate, a POKE is required to initiate double speed operation. The CoCo3 was still capable of bing connected to a TV, but also had composite and RGB (analog) video output. The RGB analog signal was a bit of a tease -- it required a specific monitor, not the then standard (and easier to get cheap used) RGB digital monitor as used by IBM PC clones. Tandy had an answer for that, they made a somewhat affordable CM-8 RGBA monitor available for $299.95. There were a few others on the market that would work, as the Amiga and some Commodore and Atari models used RGBA as well. I believe Tandy decided on RGBA as it was cheaper to pair with TV and composite output.

Another new feature is that the CoCo3 operates in all RAM mode all the time. This means that the ROMs are copied into RAM and run from there. Older CoCos that were upgraded to 64K could be run that way, but typically reserved part of their 64K memory access to read the ROMs. Part of the reason for all RAM mode was due to the copyright restrictions on Extended Color BASIC, which was written by Microsoft. A third party, Microware, wrote Super Extended Color BASIC (SECB), which was included with every CoCo3. In order to get around any copyright issues the additioanal SECB commands and enhancements were patched into ECB when in RAM, so the standard ECB code was left alone.

The CoCo 3 was last listed in the first 1991 Tandy Computer Catalog (RSC-22) at $199.95 for the 128K version. A 512K upgrade board with no RAM chips was $39.95, ram chips were $59.95. The CM-8 monitor still listed for $299.95. The listing takes up about 1/3 of page 50 (if you include the data cassette player listing) and the CoCo isn't even listed in the quick index. Tandy issued two more Computer Catalogs in 1991, RSC-22A and RSC-22E. The CoCo is not listed in RSC-22A. RSC-22E is an educational market catalog and has one page of Color Computer software.