The keyboard consists of a rubber mat wit carbon pills and a foil with conductive ink traces. The carbon pill is pressed against the traces, closing the contact. Primary failure mode is electromigration, causing one key to stick and block a row. The secondary failure mode is broken tracks. Tracks can be repaired with conductive ink, shorts can be fixed by carefully scraping. Ebay auction
https://www.ebay.de/itm/293192600733 (not mine) includes some pictures of the keyboard foil.
Scancode mapping is as follows:
left softkeys: 10/Q, 11/W, 12/E, 13/R, 14/T, 15/Y, 16/U, 17/I, 18/O
right softkeys: 1E/A, 1F/S, 20/D, 21/F, 22/G, 23/H, 24/J, 25/K, 26/L
lower softkeys: 3B/F1, 3C/F2, 3D/F3, 3E/F4, 3F/F5, 40/F6, 41/F7, 42/F8, 0C/-
control group:
0E/<--, 52/NumIns
31/N, 30/B
2F/V, 2E/C
2C/Z, 2D/X
functon group: 19/P, 1A/[, 1B/]
system group: 1B/\, 28/', 27/;
number block:
08/7, 09/8, 0A/9, 86/F12
05/4, 06/5, 07/6, 85/F11
02/1, 03/2, 04/3, 44/F10
0B/0, 34/., 35//, 43/F9
01/ESC, 1C/Enter, 0F/Tab
cursor block:
4B/left, 48/up, 4D/right, 50/down
Note that the CMU's front module computer is a generic PC that runs MS-DOS. You can connect everything to the USB that fits, but without a proper MS-DOS device driver nothing will be recognized. For file management, you can install Volkov Commander (or Norton Commander). With PS/2 mouse emulation turned on in the BIOS and a PS/2 mouse driver in CONFIG.SYS, this will accept a mouse. However, the CMU software does not support it.
Patrick