The K90 uses keyboard usage codes for special keys. Some keys have different usage codes depending on status.
| Usage | Key |
|---|---|
| 0xd0 | G1 |
| 0xd1 | G2 |
| 0xd2 | G3 |
| 0xd3 | G4 |
| 0xd4 | G5 |
| 0xd5 | G6 |
| 0xd6 | G7 |
| 0xd7 | G8 |
| 0xd8 | G9 |
| 0xd9 | G10 |
| 0xda | G11 |
| 0xdb | G12 |
| 0xdc | G13 |
| 0xdd | G14 |
| 0xde | G15 |
| 0xdf | G16 |
| 0xe8 | G17 |
| 0xe9 | G18 |
| 0xf1 | M1 |
| 0xf2 | M2 |
| 0xf3 | M3 |
| 0xf4 | Meta key lock (switching off) |
| 0xf5 | Meta key lock (switching on) |
| 0xf6 | MR (start recording) |
| 0xf7 | MR (stop recording) |
| 0xfa | Light (off) |
| 0xfb | Light (33%) |
| 0xfc | Light (66%) |
| 0xfd | Light (100%) |