Difference between revisions of "Enhanced ULA Palette Extension"
(Rewording a bit and adding info from web docs.) |
(Fixing read/write vs index auto increment description, thanks to Garry help on Facebook to identify the mistake) |
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| Line 3: | Line 3: | ||
|Readable=Yes | |Readable=Yes | ||
|Writable=Yes | |Writable=Yes | ||
| − | |ShortDesc=Use to set | + | |ShortDesc=Use to set 9-bit (2-byte) colours of the ULANext palette, or to read second byte of colour. |
}} | }} | ||
| − | Two consecutive | + | Two consecutive writes are needed to write the 9 bit colour: |
| − | * 1st | + | * 1st write: bits 7-0 = RRRGGGBB |
| − | * 2nd | + | * 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 {{NextRegNo|$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 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. | 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. | ||
| − | After the | + | 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. | ||
The modified palette remains until a Hard Reset. | The modified palette remains until a Hard Reset. | ||
Revision as of 23:42, 6 January 2019
| Number | $44 |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Use to set 9-bit (2-byte) colours of the ULANext 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 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.
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.