ULA Control Port

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Number $xxFE
Decimal 254
Short desc. Controls border color and base Spectrum audio settings.
Bit Mask
Readable No
Writable Yes

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).