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39-year-old Radio Shack laptop gets new CPU, keeps original screen

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The 1983-era Model 100 TRS-80 was an action hero, exploding on the scene.
Zoom / The 1983-era Model 100 TRS-80 was a hero in the action, and it exploded massively on the scene.

Faced with a broken RadioShack laptop since 1983, Stephen Cass hasn’t gotten over the IEEE Spectrum editor. Instead, he pulled out the logic board and replaced it with a modern microcontroller so he could control the old monitor. Cass wrote about his adventure in detail at Spectrum last week.

Cass made his work on the RadioShack TRS-80 Model 100 – one of the first laptops ever produced – which features a one-piece “board” shape designed by Kyocera and released as the NEC PC-8201 in Japan. Its claim to fame wasn’t its small portable size (2 inches thick and 3.9 pounds), but its impressive keyboard paired with its ability to run for up to 20 hours on four AA batteries.

The Model 100 featured a 2.4MHz Intel 80C85 CPU, 8 to 32KB of RAM, and an eight-line, 40-character monochrome LCD without backlight. It doesn’t look like much compared to today’s portable monsters, but journalists loved the Model 100 because they could easily write stories on the go with the built-in text editor. It also included Microsoft BASIC, a terminal program, and an address book in ROM.

Excerpt from the 1983 Radio Shack computer catalog page showing the TRS-80 Model 100 laptop.
Zoom / Excerpt from the 1983 Radio Shack computer catalog page showing the TRS-80 Model 100 laptop.

While some people are upgrading the 100s with new LCDs and CPUs (keeping only the case and keyboard), Cass decided to experiment with an interface with a vintage portable 240 x 64 pixel display. He found it particularly difficult because the computer handles screen driving in an unconventional way compared to current LCD panels.

Cass writes: “The LCD of the M100 is 10 separate monitors, each controlled by its own HD44102 driver chip.” “All driver chips are responsible for a 50 x 32 pixel area of ​​the screen, except for two chips on the right side that only control 40 x 32 pixels.” Cass says its designers chose this method because it speeds up text rendering with limited memory.

After working on the monitor protocol, Cass built an interface between the monitor and the modern Arduino Mega 2560 microcontroller. Now that the project is in place, it can display and pass bitmap graphics on the Model 100’s LCD. Its next step would be to try to connect the display and keyboard (with a Teensy 4.1 development board to handle keyboard connections) to a Raspberry Pi 4 compute module, making it possible to create a machine Portable strong with an antique feel.

You can read more about the technical details of his project on the IEEE Spectrum website. Good luck, Stephen!

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