Enhanced ULA Palette Extension

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Number $44
Readable Yes
Writable Yes
Short Description Use to set 9-bit (2-byte) colours of the Enhanced ULA palette, or to read second byte of colour.

Two consecutive writes are needed to write the 9 bit colour:

  • 1st write: bits 7-0 = RRRGGGBB
  • 2nd write: bits 7-1 are reserved, must be 0 (except bit 7 for Layer 2), bit 0 = lsb B

(to detect whether first or second write is expected, one can read bit 7 of Machine Type Register ($03), in case your code is not aware of current state)

If writing the Layer 2 palette colour, in the second byte, bit 7 is "priority" bit. Priority colour will be always on top (drawn above all other layers), even on a priority arrangement like "USL" . If you need the exact same colour with priority and non priority, you will need to program the same colour twice, changing bit 7 to 0 for the non priority colour alternative.

After the write of second byte, the palette index is auto-incremented, if the auto-increment is enabled by Enhanced ULA Control Register ($43).

The read will always read the second byte of colour (%p000000B) and it will not modify the index.

The modified palette remains until a Hard Reset.