Palettes: Difference between revisions

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[[File:Palmap.png|thumb|Palette organisation]]
[[File:Palmap.png|thumb|Palette organisation]]
There are 2 banks (one usable at a time) of 256 palettes available. Each palette has 16 entries, the first is the transparent index ("color 0"), the 15 others are real colors, made of 16bit RGB definitions.
There are 2 banks (one usable at a time) of 256 palettes available. Each palette has 16 color entries, the first being the transparent index ("color 0"), the 15 others are real colors, made of 16-bit RGB definitions.


[[Sprites|Sprite]] tiles can use any of the 256 palettes, while the [[Fix layer|fix]] tiles can only use the first 16.
[[Sprites|Sprite]] tiles can use '''any''' of the 256 palettes, while the [[Fix layer|fix]] tiles can '''only use the first 16'''.


The maximum number of colors on screen without [[timer interrupt]] tricks is: 256 palettes * 15 colors = '''3840''' (out of 2^16 = 65536).
The maximum number of colors on screen without [[timer interrupt]] tricks is: 256 palettes * 15 colors = '''3840''' (out of 2^16 = 65536).
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See [[colors]].
See [[colors]].


=Special colors=
=Access=


There are two special colors used:
Palettes are located at $400000 in the [[68k memory map]]. They're physically stored in the [[palette RAM]].


*The first color of the palette bank ($400000) is the [[reference color]] for the video output. It has to be $8000 (black) otherwise monitors won't be happy and other colors won't be displayed correctly.
Byte writes are allowed, but the value will be written to both bytes of the word (/WE pins are tied together).
*The last color of the palette bank ($401FFE) is the [[backdrop color]] (the color of the backmost "layer" on the screen). Caused by line buffers in {{Chipname|NEO-B1}} being cleared to $FFF (Last color of last palette).


=Access=
The palettes can be read and written at full speed at any time. During active display, since the CPU has priority over rendering, the color read or written will be displayed during at least one pixel, resulting in noticeable "snow" if multiple colors are updated. A workaround is to update the palettes only during blanking (horizontal or vertical), over multiple frames if necessary.


Palettes are located at $400000 in the [[68k memory map]], and they're physically stored in the [[palette RAM]].
The bank can be set by doing a byte write to registers {{Reg|REG_PALBANK1}} or {{Reg|REG_PALBANK0}}.


Byte access may be allowed, but it will trash the corresponding word's other byte (/WE are tied together). Maybe {{Chipname|NEO-C1}} doesn't assert {{Sig|PAL|PAL}} during byte access ?
=Special colors=


The palettes can be read and written at any time. During active display, since the CPU has priority over rendering, the color read or written will be displayed during at least one pixel, resulting in noticeable "snow" if multiple colors are updated. A workaround is to update the palette only during blanking (horizontal or vertical), over multiple frames if necessary.
There are two special colors used:


The bank can be set by writing a byte to registers {{Reg|REG_PALBANK1}} or {{Reg|REG_PALBANK0}}.
* The first color of the palette bank ($400000) is the [[reference color]] for the video output. It always has to be pure black ($8000) otherwise monitors won't be happy and other colors won't be displayed correctly.
* The last color of the palette bank ($401FFE) is the [[backdrop color]], the color of the backmost "layer" on the screen. Caused by line buffers in {{Chipname|NEO-B1}} being cleared to $FFF (referencing the last color of the last palette).


[[Category:Video system]]
[[Category:Video system]]

Revision as of 21:35, 23 June 2018

Palette organisation

There are 2 banks (one usable at a time) of 256 palettes available. Each palette has 16 color entries, the first being the transparent index ("color 0"), the 15 others are real colors, made of 16-bit RGB definitions.

Sprite tiles can use any of the 256 palettes, while the fix tiles can only use the first 16.

The maximum number of colors on screen without timer interrupt tricks is: 256 palettes * 15 colors = 3840 (out of 2^16 = 65536).

Color format

See colors.

Access

Palettes are located at $400000 in the 68k memory map. They're physically stored in the palette RAM.

Byte writes are allowed, but the value will be written to both bytes of the word (/WE pins are tied together).

The palettes can be read and written at full speed at any time. During active display, since the CPU has priority over rendering, the color read or written will be displayed during at least one pixel, resulting in noticeable "snow" if multiple colors are updated. A workaround is to update the palettes only during blanking (horizontal or vertical), over multiple frames if necessary.

The bank can be set by doing a byte write to registers REG_PALBANK1 or REG_PALBANK0.

Special colors

There are two special colors used:

  • The first color of the palette bank ($400000) is the reference color for the video output. It always has to be pure black ($8000) otherwise monitors won't be happy and other colors won't be displayed correctly.
  • The last color of the palette bank ($401FFE) is the backdrop color, the color of the backmost "layer" on the screen. Caused by line buffers in NEO-B1 being cleared to $FFF (referencing the last color of the last palette).
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