ULA Control Port
From SpecNext official Wiki
| Number | $xxFE |
|---|---|
| Decimal | |
| Short desc. | Controls border color and base Spectrum audio settings. |
| Bit Mask | |
| Readable | No |
| Writable | Yes |
| Subsystem |
When written to, adjusts the border color and audio devices as follows (soft reset = 0):
| Bit | Function |
|---|---|
| 0-2 | Border color |
| 3 | MIC output (saving via audio jack) |
| 4 | EAR output (connected to internal speaker) |
| 5-7 | Unused |
Reading the port with certain particular high bytes will read the keyboard - see Keyboard ($**FE / 254). Bit 6 of the ULA byte is always the EAR input (signal from tape audio jack - also input from Pi digital audio is now mixed in, since 3.0 cores).