Difference between revisions of "Enhanced ULA Palette Extension"
(Created page with "{{NextRegister |Number=$44 |Readable=No |Writable=Yes |ShortDesc=Holds the additional blue color bit for 512 color palettes. }}") |
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{{NextRegister | {{NextRegister | ||
|Number=$44 | |Number=$44 | ||
| − | |Readable= | + | |Readable=Yes |
|Writable=Yes | |Writable=Yes | ||
| − | |ShortDesc= | + | |ShortDesc=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 {{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 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. | ||
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.