https://github.com/osresearch/modelf

USB interface for the IBM Model F AT keyboard
https://github.com/osresearch/modelf

arduino keyboard model-f retrocomputing teensy usb-hid

Last synced: 8 months ago
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USB interface for the IBM Model F AT keyboard

• Host: GitHub
• URL: https://github.com/osresearch/modelf
• Owner: osresearch
• License: gpl-2.0
• Created: 2017-06-17T22:22:20.000Z (almost 9 years ago)
• Default Branch: master
• Last Pushed: 2017-06-18T01:18:25.000Z (almost 9 years ago)
• Last Synced: 2025-04-16T00:45:02.471Z (about 1 year ago)
• Topics: arduino, keyboard, model-f, retrocomputing, teensy, usb-hid
• Language: Arduino
• Size: 19.5 KB
• Stars: 12
• Watchers: 3
• Forks: 5
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md

Awesome Lists containing this project

README

          
IBM Model F Keyboard Interface

===

![IBM Model F USB keyboard](https://farm5.staticflickr.com/4221/35330162436_b938f6c4fd_z_d.jpg)

This is a Arduino/Teensy based adapter for the classic IBM Model F AT

keyboard to a modern USB HID device.  It doesn't require any permanent

modifications to the keyboard and fits entirely inside the spacious

housing.

There are some minor annoyances with this keyboard compared to the

more common Model M:

* There are no arrow keys!

* The escape key is on the numeric keypad, rather than by the tilde.

* The function keys are on the left side, making the keyboard quite wide.

* The backspace is quite small.

* The `\\` and `|` key is oddly positioned next to the backspace.

* The `F` and `J` keys do not have any locator dots.

Wiring

---

![Teensy and Model F PCB](https://farm5.staticflickr.com/4252/35239419941_2bf131733b_z_d.jpg)

There are only four wires necessary to connect the keyboard to the Teensy.

Clock, Data, Power and Ground.  The Model F PCB has long two-row right

angle pin header connector and its cable connected via a 3x2 connector

(with a missing pin) to the far side.  The four pins that we need are:

   Reset (NC)    NC        +5V

   Clock/D0      Ground    Data/D1

The Clock connects to Teensy D0, data to Teensy D1.  Power and Ground

use the USB +5V line.

Protocol

---

The clock and data are open collector, so the AVR is configured with

input pullups and watches for the falling edge on the clock to indicate

that data is arriving.

According to [Craig Peacock's site](http://retired.beyondlogic.org/keyboard/keybrd.htm)



The transmission of data in the forward direction, ie Keyboard to Host is

done with a frame of 11 bits. The first bit is a Start Bit (Logic 0)

followed by 8 data bits (LSB First), one Parity Bit (Odd Parity) and a Stop

Bit (Logic 1). Each bit should be read on the falling edge of the clock.



The Teensy busywaits for the falling edge of the clock to indicate

the stop bit, then reads the remaining ten bits in the frame.  It checks

the parity and has a lookup table of IBM scancodes to USB keycodes that

it uses to generate the HID messages.

We can also generate commands to the keyboard to query its version,

enable the LEDs, etc.  There appears to be some sort of problem with

the way that we're dealing with the bus, but it mostly works.

Sometimes toggling caps-lock/num-lock at a high rate causes problems.

teensy won't program, so once the case is closed up it is hard to iterate