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

The iPad of the 1980s

Hobbyist and IEEE editor Stephen Cass upgrades a broken laptop from 1983.

A 1983-era TRS-80 Model 100 as action hero, exploding onto the scene.

Enlarge / A 1983-era TRS-80 Model 100 being an action hero, dramatically exploding onto 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 today’s microcontroller so he could control the vintage screen. Cass wrote about his adventure at length for Spectrum the other day.

Cass performed his operation on a Radio Shack TRS-80 Model 100among the first laptops ever producedwhich includes a one-piece “slate” form created by Kyocera and released because the NEC PC-8201 in Japan. Its claim to fame had not been only its small portable size (at 2 inches thick and 3.9 lbs), but having an excellent keyboard paired using its capability to run for 20 hours on four AA batteries.

The Model 100 included a 2.4 MHz Intel 80C85 CPU, 8 to 32K of RAM, and an eight-line, 40-character monochrome LCD without backlight. It generally does not appear to be much in comparison to today’s portable beasts, but journalists loved the Model 100 since they could comfortably write stories on the run which consists of built-in text editor. In addition, it included Microsoft BASIC, a terminal program, and an address book in ROM.

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

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

Although some people upgrade Model 100s using new LCD screens and CPUs (keeping only the case and keyboard), Cass made a decision to attempt an interface with the portable’s vintage 24064 pixel display. He found it particularly challenging as the computer handles driving the display within an unconventional way in comparison to today’s LCD panels.

“The M100s LCD is actually 10 separate displays, each controlled by its HD44102 driver chip,” Cass writes. “The driver chips are each in charge of a 50-by-32-pixel region of the screen, aside from two chips at the right-hand side that control only 40 by 32 pixels.” Its designers chose this technique, Cass says, since it boosts text display with limited available memory.

Okay, heres my demo: first it fills and clears the screen by writing to all or any chips simultaneously, then loads a complete screen bitmap as fast because the display can go, then uses hadware bank switching and partial refresh to fast scroll!

stephencass (@stephencass) September 21, 2022

After training the protocol for the screen, Cass built an interface between your screen and today’s Arduino Mega 2560 microcontroller. Because the project stands now, he is able to display and scroll bitmapped graphics onto the Model 100’s LCD. His next thing is to make an effort to interface the screen and keyboard (with a Teensy 4.1 development board to take care of keyboard communications) to a Raspberry Pi 4 compute module, which may make for a robust portable machine with an antique feel.

It is possible to read more concerning the technical information on his project on IEEE Spectrum’s website. All the best, Stephen!

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