One of the more surprising chips ever had to be the GIME chip used in the Tandy Color Computer 3; we're still learning about it. It is unfortunate, though, that it was a very proprietary chip, that was only available to Tandy for the Color Computer 3 (it wasn't sold to 3rd parties). Furthermore, with it being a tricky beast, emulation of it is difficult - the information that is available is what certain people have reverse engineered, plus what was known from service manuals and the like from back in the day (the design materials are long gone).
For instance, back in the late 1990s or early 2000s (I forget which), there were rumors floating around about a mysterious "256 color" mode on the Color Computer 3; this on a machine which officially had only 64 possible colors! The rumor was spurred on by an individual who claimed to have seen it when they worked at Microware, and that it involved some trickery with certain registers.
People played around with this thing forever, to no avail. There had been other methods used to get many more colors on the display than what was officially available; many involved high-speed assembler being used to change the palette rapidly during a horizontal blank, as well as the vertical blank. An early "hack" enabled the ability to see all 64 colors on-screen at once. Other "hacks" allowed still images to be displayed that had thousands of colors. Nothing quite as impressive as the Amiga's HAM and HAM-E modes, but then again this was being done on a 2 MHz 8-bit CPU...
Another method back in the day, when the Rainbow Magazine was being published, used the composite output or NTSC output to a TV to get more colors on-screen via dithering four colors in the 640x192 mode on the Color Computer 3. Little did anyone know at the time how close they were to discovering an amazing mode. I played with it myself, and it never occurred to me or anyone else.
You see, back in the early days of the original Color Computer, there was a display mode (the highest resolution mode on that machine) of 256x192 pixels, 2 colors (black and white; well actually something close to white called "buff"). When displayed on a television, and placing alternating pixels of black and white together, you could get other colors of red and blue, due to NTSC artifacting. Many games utilized the mode; most had a method where you had to hit reset multiple times to get the order of the colors to switch, in order for the game to have proper colors. What you lost was resolution (the resolution effectively became 128x192), but the gaining of colors in the mode was a popular tradeoff.
On the Color Computer 3, that was how it was recently (late 2009) discovered that one could get 256 colors! By using the 640x192 4 color mode on a composite monitor or television, and using a palette of black, dark gray, light gray, and white, while alternating the pixels properly, the NTSC artifacting takes over; you end up with a 160x192 256 color display.
People have converted various images to the dithering patterns necessary to display them; while I haven't personally seen a real image yet (I don't have my Color Computer 3 system set up currently), the digital photos taken of composite monitors have been amazing to see; they say the actual images are even better. While I have found this to be an amazing discovery, it will always be on my mind as to "what if" it had been discovered back when the system was being sold at Radio Shack (1986-1991).
Ah, well...
