It’s been a while since we actually completed this project, but here’s the video finally. Basic HC12 dev board, PS2 controller on the SPI bus and the LCD display on two of the I/O ports.

All the code is on GitHub for your reusing pleasure: http://github.com/ckoehler/HC12-Tetris

Note that you need the exact hardware to reproduce it, especially the display and an HC12. Maybe I will get around looking up the model # of the LCD display someday.