Faced with a broken 1983 Radio Shack laptop, IEEE Spectrum editor Stephen Cass didn’t throw it away. Instead, he took out the logic board and replaced it with a modern microcontroller so he could control the old screen. Cass wrote about his adventure in detail for Spectrum last week.
Cass performed his operation on a Radio Shack TRS-80 Model 100, one of the first portable computers ever produced, featuring a one-piece “slate” shape designed by Kyocera and released as the NEC PC-8201 in Japan. Its claim to fame wasn’t just its small portable size (at 2 inches thick and 3.9 pounds), it has a great keyboard combined with its ability to run up to 20 hours on four AA batteries.
The 100 model included a 2.4 MHz Intel processor. 80C85 CPU, 8 to 32K of RAM, and an eight-line, 40-character monochrome LCD display without backlight. It doesn’t look like much compared to today’s portable beasts, but journalists loved the Model 100 because they could conveniently 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.
While some people upgrade the Model 100 using new LCD screens and CPU (keeping just the case and keyboard), Cass decided to try an interface with the notebook’s vintage 240×64 pixel display. She found it particularly challenging because the computer drives the screen in an unconventional way compared to today’s LCD panels.
“The LCD on the M100 is actually 10 separate screens, each controlled by its own HD44102 controller chip,” writes Cass. “Each of the controller chips is responsible for a 50-by-32-pixel region of the screen, except for two chips on the right side that control only 40-by-32 pixels.” Its designers chose this method, says Cass, because it speeds up the display of text with limited available memory.
Okay, here’s my demo: first it fills and clears the screen by writing to all the chips at once, then it loads a full screen bitmap as fast as the screen can go, then it uses hardware bank switching and a partial upgrade for fast scrolling. pic.twitter.com/VbF2vgaG9L
– stephencass (@stephencass) September 21, 2022
After working out the protocol for the screen, Cass built an interface between the screen and a modern Arduino Mega 2560 microcontroller As the project now stands, you can display and scroll bitmap graphics on the Model 100 LCD. Your next step will be to try to interface the display and keyboard (with a Teenager 4.1 development board to handle keyboard communications) to a Raspberry Pi 4 compute module, which would make it 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 Stephen!