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

enlarge / A 1983-era TRS-80 Model 100 as an action hero, exploding dramatically on the scene.

Confronted with a broken Radio Shack laptop from 1983, IEEE Spectrum editor Stephen Cass didn’t throw it away. Instead, he pulled out the logic board and replaced it with a modern microcontroller so he could control the vintage display. Cass wrote extensively about his adventure for Spectrum last week.

Cass ran his operation on a Radio Shack TRS-80 Model 100 – one of the first laptops ever produced – with a one-piece “slate” shape designed by Kyocera and released as the NEC PC-8201 in Japan. Its claim to fame was not only its small portable size (at 2 inches thick and 3.9 lbs), but also having a great keyboard coupled with its ability to run for up to 20 hours on four AA batteries.

The Model 100 included a 2.4MHz Intel 80C85 CPU, 8 to 32K RAM, and an eight-line, 40-character monochrome LCD display with no backlight. It doesn’t sound like much compared to today’s portable beasts, but journalists loved the Model 100 because they could easily write stories on the go using its built-in text editor. It also included Microsoft BASIC, a terminal program, and an address book in ROM.

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Excerpt from a 1983 Radio Shack computer catalog page featuring the TRS-80 Model 100 laptop.
enlarge / Excerpt from a 1983 Radio Shack computer catalog page featuring the TRS-80 Model 100 laptop.

While some people are upgrading Model 100s with new LCD screens and CPUs (with just the case and keyboard), Cass decided to try an interface with the portable’s vintage 240×64-pixel display. He found it particularly challenging because the computer controls the display in an unconventional way compared to current LCD panels.

“The M100’s LCD is actually made up of 10 separate displays, each controlled by its own HD44102 driver chip,” Cass writes. “The driver chips are each responsible for an area of ​​50 by 32 pixels on the screen, except for two chips on the right that only control 40 by 32 pixels.” The designers chose this method, Cass says, because it speeds up text rendering with limited available memory.

After working out the protocol for the screen, Cass built an interface between the screen and a modern Arduino Mega 2560 microcontroller. As it stands now, the project can display and scroll bitmap images on the Model 100’s LCD. His next step will be to try and pair the screen and keyboard (using a Teensy 4.1 keyboard communications dev board) to a Raspberry Pi 4 computer module, which would make for a powerful portable machine with a vintage feel.

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

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