Reverse engineering the 1988 NeXT keyboard protocol #Keyboards

Spencer tackles reverse engineering the 1988 NeXT keyboard protocol:

Steve Jobs’ NeXT computer company made a keyboard in 1988. With no prior electronics experience, I tried to get it to work over USB. To do so, I had to go way deeper than I ever expected – all the way back over 100 years to broadcast radio standards from the 1920s. I learned tons and tons, and had a lot of fun.

Happily, other people have worked to get these old NeXT non-ADB keyboards to work over USB. There’s a quite thorough tutorial on Adafruit, complete with code.

I eagerly installed the tutorial’s software and… nothing really worked quite right. Keys sometimes worked, but sometimes didn’t. The “A” key worked great, but if I pressed “X” or “C” then I would never get any signals again until I unplugged it and replugged it. Something was wrong.

Spencer found an article from someone named Drak who seemed to have similar doubts about the timing, and who noted that the time interval might be as high as 54 microseconds.

And then Spencer found that the open source TMK keyboard firmware has an implementation for non-ADB NeXT keyboards, with an intriguing comment attached:

/* The keyboard sends signal with 50us pulse width on OUT line
 * while it seems to miss the 50us pulse on In line.
 * next_kbd_set_leds() often fails to sync LED status with 50us
 * but it works well with 51us(+1us) on TMK converter(ATMega32u2) at least.
 * TODO: test on Teensy and Pro Micro configuration
 */

Some detailed examination found:

  • The signal looks like it really is two 9-bit messages, separated by a 1-pulse-width boundary.
  • The pulses were extremely consistently 52.74 +/- 0.02 microseconds wide.
  • When I told my Arduino to sleep for 51 microseconds, it was generally sleeping for either 56.2 or 61.3 microseconds. That seemed to easily be bad enough to cause lots of problems.

Inside is a 455KHz oscillator and 455 kHz / 24 = 18,958 hertz, leading to the conclusion:

The NeXT non-ADB keyboards have a pulse width of 52.74 microseconds, because they send data every 24 ticks of a 455 kHz clock.

Read this amazing article here and see the code here.


Halloween season is here!
Halloween season is here! Check out all the posts, gift guides, and more!

Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards

Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.

Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7:30pm ET! To join, head over to YouTube and check out the show’s live chat and our Discord!

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Join over 38,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org


New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — NewProducts Featuring Adafruit RP2350 22-pin FPC HSTX to DVI Adapter for HDMI Displays!

Python for Microcontrollers – Adafruit Daily — Python on Microcontrollers Newsletter: Adafruit Grand Opening, Profile MicroPython Memory and More! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi — Classic editor

EYE on NPI – Adafruit Daily — EYE on NPI Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

Adafruit IoT Monthly — Garden Lights, Bluetooth 6.0, and more!

Maker Business – Adafruit Daily — A look at Boeing’s supply chain and manufacturing process

Electronics – Adafruit Daily — When do I use X10?

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at AdafruitDaily.com !



No Comments

No comments yet.

Sorry, the comment form is closed at this time.