Faced with a broken 1983 Radio Shack laptop, IEEE Spectrum editor Steven Kass did not throw it away. Instead, he pulled out the logic board and replaced it with a modern microcontroller to drive the old screen. Kass wrote in detail about his adventure for the Spectrum last week.
Kass performed his operation on the Radio Shack TRS-80 Model 100—one of the first laptops ever produced—which features 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 (2 inches thick and 3.9 pounds), but that it had an excellent keyboard, combined with the ability to run up to 20 hours on four AA batteries.
The Model 100 included a 2.4 MHz Intel 80C85 processor, 8 to 32 KB of RAM, and a non-backlit, eight-line, 40-character monochrome LCD. That’s not much compared to today’s portable beasts, but journalists liked the Model 100 because they could comfortably write articles on the go using the built-in text editor. It also included Microsoft BASIC, a terminal program, and a ROM address book.
While some people are upgrading the Model 100 with new LCD screens and processors (leaving only the case and keyboard), Kass decided to try the interface with a vintage 240×64 pixel portable display. He found this particularly challenging because the computer controls the display in an unconventional way compared to today’s LCD panels.
“The M100 LCD is actually 10 individual displays, each driven by its own HD44102 driver chip,” Kass writes. “Each of the driver chips is responsible for a 50 by 32 pixel area of the screen, with the exception of the two chips on the right side, which only control 40 by 32 pixels.” The developers chose this method, Kass says, because it speeds up text rendering when available memory is limited.
Okay, here’s my demo: it first fills and clears the screen by writing all the chips at once, then loads a full screen bitmap as fast as the display can handle, then uses hardware bank switching and partial refresh for fast scrolling! pic.twitter.com/VbF2vgaG9L
— Stephencass (@stephencass) September 21, 2022
After developing a protocol for the screen, Kass built an interface between the screen and a modern Arduino Mega 2560 microcontroller. In the current state of the project, he can display and scroll bitmap graphics on the Model 100 LCD. His next step is to try to communicate the screen and keyboard (with the Teensy 4.1 debug board). to communicate with the keyboard) with the Raspberry Pi 4 compute module, which will allow you to create a powerful portable machine in vintage style.
You can read more about the technical details of his project on the IEEE Spectrum website. Good luck Stepan!