Open Source Code
A few years ago an extraordinary programmer, engineer, circuit designer, and IBM keyboard enthusiast, known on the forums as xwhatsit, wanted to replace the controller on some of his old IBM keyboards with a modern, NKRO-capable, USB native controller that could be completely customized with custom key values, layouts, and layers. In 2014 xwhatsit achieved his vision and released his project with an open source GPL3 license.
His project single handedly made it possible to use some of the older IBM keyboards as well as made it possible for these new F77 and F62 keyboards to exist.
This Model F project uses the most recent stable version of xwhatsit's software and hardware, which has run for over a year and a half on old IBM keyboards around the world. The source code, GUI software, and firmware are unmodified for this project and can be freely downloaded from xwhatsit's web site.
Future firmware versions can be loaded onto the ATMega chip inside each F62 and F77 keyboard using Atmel's Flip 3.4.7 software.
Some links of interest: