POR column indicates whether a register has power on reset. A "N" indicates that the contents of a register are undefined at power on.
A colour in the palette is coded in 2 bytes:
* For first byte, bits7..4 are blue value, bits3..0 are red value
* For second byte, bits7..4 are ignored, bits3..0 are green value
Analog joystick axes are unsigned 6-bit values. Bits7..6 are always 0.