Difference between revisions of "Enhanced ULA Palette Extension"

Latest revision as of 11:38, 3 November 2024

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.

Writes to nextreg 0x40, 0x41, 0x43 reset to the 1st write.

The modified palette remains until a Hard Reset.

@@ Line 3: / Line 3: @@
 |Readable=Yes
 |Writable=Yes
-|ShortDesc=Use to set/read 9-bit (2-byte) colours of the ULANext palette.
+|ShortDesc=Use to set 9-bit (2-byte) colours of the Enhanced ULA palette, or to read second byte of colour.
 }}
-Two consecutive reads/writes are needed to read/write the 9 bit colour:
+Two consecutive writes are needed to write the 9 bit colour:
-* 1st read/write: bits 7-0 = RRRGGGBB
+* 1st write: bits 7-0 = RRRGGGBB
-* 2nd read/write: bits 7-1 are reserved, must be 0 (except bit 7 for Layer 2), bit 0 = lsb B
+* 2nd write: bits 7-1 are reserved, must be 0 (except bit 7 for Layer 2), bit 0 = lsb B
-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 Sprites), even on an "SLU" priority arrangement. 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 variant.
+(to detect whether first or second write is expected, one can read bit 7 of {{NextRegNo|$03}}, in case your code is not aware of current state)
-After the two consecutive writes the palette index is auto-incremented if the auto-increment is enabled by {{NextRegNo|$43}}.
+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 {{NextRegNo|$43}}.
+The read will always read the second byte of colour (%p000000B) and it will not modify the index.
+Writes to nextreg 0x40, 0x41, 0x43 reset to the 1st write.
 The modified palette remains until a Hard Reset.