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IBM 4704 to USB keyboard converter

This firmware converts IBM 4704 keyboard protocol to USB HID. Keyboard initialization process takes a few seconds at start up. You may need to plug USB cable after hooking up your keyboard to the converter.

TMK Converter for IBM4704 is available here:


  • 2016/09/30 Unimap editor support
  • 2015/09/07 Added keymap for Alps 102-key. Thanks, tai @ geekhack!
  • 2015/05/05 Added keymaps for 107-key, 77-key and 50-key. Thanks, orihalcon @ geekhack!
  • 2015/05/19 Fixed a protocol handling bug.

Supported Keyboard

IBM capacitive switch models:

Alps switch(vintage Green) models:


Keyboard Plug from front:

\ N 2 3 4 5 /
 \ N N N N /
2   GND
3   VCC 5V
4   DATA
N   No connection/No pin.


In case of using ATMega32U4/U2

  1. Supply power with VCC and GND.
  2. Connect CLOCK to PD1 and DATA to PD0. You can change pin with config.h.
  3. Optionally you may need pull-up register. 1KOhm probably work.

TMK Converter can supports IBM 4704.

Build Firmware

Just run make:

$ make -f <makefile>

For TMK Converter rev.1 use Makefile.rev1 as makefile:

$ make -f Makefile.rev1

For TMK Converter rev.2 use Makefile.rev2 as makefile:

$ make -f Makefile.rev2

To select keymap:

$ make -f <makefile> KEYMAP=[plain|alsp102key|...]

To indentify your TMK Converter revision see this.


Several version of keymap are available in advance but you are recommended to define your favorite layout yourself. To define your own keymap create file named keymap_<name>.c and see keymap document(you can find in top and existent keymap files.

Use KEYMAP_ALPS102() to define your keymap for Alps models.