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files/docs/snes/tile_format.txt
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files/docs/snes/tile_format.txt
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----------------------------
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By DAX on 28/2/93
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This is a short text file on how the data for the gfx on the SNES are
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set up..
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Everything is based around an 8x8 pixel 'Tile' and thinking in terms of
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tiles makes the whole thing a lot easier.
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4 Colour mode - 2 Bitplanes
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---------------------------
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If you split the screen into 8x8 pixel tiles, the order of the graphics data
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is tile 0,1,2,3,4 etc.(with tile 0 being the first, and 1 being the one on
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the right of it.)
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Then for each tile, the data is stored as shown below.
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00 01 02 03 04 05 06 07
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10 11 12 13 14 15 16 17 Each number representing one pixel in
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20 21 22 23 24 25 26 27 the 8x8 tile.
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30 31 32 33 34 35 36 37
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40 41 42 43 44 45 46 47
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50 51 52 53 54 55 56 57
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60 61 62 63 64 65 66 67
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70 71 72 73 74 75 76 77
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The data is stored in the SNES binary in the following format.
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Bitplane 0 .. Line 00-07 (One Byte)
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Line 10-17
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Line 20-27
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Line 30-37
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Line 40-47
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Line 50-57
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Line 60-67
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Line 70-77
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then Bitplane 1 .. Line 00-07
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Line 10-17
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Line 20-27
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Line 30-37
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Line 40-47
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Line 50-57
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Line 60-67
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Line 70-77
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then comes the data for the next tile (the one on the right).etc.
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16 Colour - 4 Bitplanes
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-----------------------
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The data for this mode is stored in the same format, with one main change.
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The data is stored in the format
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Bitplane 0 .. Line 00-07
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Line 70-77
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Bitplane 1 .. Line 00-07
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Line 70-77
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Bitplane 2 .. Line 00-07
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Line 70-77
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Bitplane 3 .. Line 00-07
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Line 70-77
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then the data for the next tile.
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256 Colour - 8 Bitplanes
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------------------------
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This is simply an expansion of the 4 and 16 colour modes.
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Bitplane 0 .. Line 00-07
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Line 70-77
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Bitplane 1 .. Line 00-07
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Line 70-77
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Bitplane 2 .. Line 00-07
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Line 70-77
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Bitplane 3 .. Line 00-07
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Line 70-77
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Bitplane 4 .. Line 00-07
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Line 70-77
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Bitplane 5 .. Line 00-07
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Line 70-77
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Bitplane 6 .. Line 00-07
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Line 70-77
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Bitplane 7 .. Line 00-07
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Line 70-77
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then the data for the next tile.
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256 Colours - Mode 7 format
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---------------------------
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This has some very major differences to the other graphics data formats
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there are two mode7 modes, normal and EXTBG, the data is stored in the
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same way in both, apart from in EXTBG the Bitplane 7 value will be a
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priority bit for the pixel, which cuts the colours down to 128.
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Each byte of 'graphics data' is actually the colour value for that pixel
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on the screen, so if the value is 64, then the colour of that pixel will
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be the contents of colour register 64.
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The data is stored in VRAM differently to the other modes, with the tile
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numbers, and the graphics data 'interleaved', starting at $0000 in VRAM,
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with alternate bytes containing one byte of tile, one byte of gfx - this
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is shown below.
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Word of VRAM. HI LO
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Bit 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
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content |------------------------------||------------------------------|
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Graphics data(CHAR DATA) Tile number(NAME)
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Because of the storing of 16 bit data in reverse format (LO-HI) this means
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that if you set the VRAM addr to $0.the first byte written should be the
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tile name for that position on screen and the second byte should be the first
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byte of the Mode7 graphics data.if the VRAM addr is set to $1 the first byte
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written will be the tile name for that position on scr, and the second byte
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should be the second byte of the mode7 graphics data.
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ETC
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In mode7 you can only have a maximum of 256 tiles, because of the fact that
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the mode7 data only takes up the first half of VRAM(32k) you can only have 16k
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of graphics data which is 256 tiles of 8x8 with 256 colours.
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This is quite a limitation, but can be used quite effectively.
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The tile numbers are stored in a format according to a 128x128 tile screen
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so tile 128($80) would be the tile below 0($0) on the screen, and so on.
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so VRAM addr $0 is the top left tile, and $1 is the one on the right of it
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$80 is the one on the left side, one row down.
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the graphics data is stored based on an 8x8 tile again.
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but slightly different.
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Each byte(pixel) is stored so...
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Bit number Contents
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0 Bitplane 0 pixel value
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1 Bitplane 1 pixel value
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2 Bitplane 2 pixel value
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3 Bitplane 3 pixel value
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4 Bitplane 4 pixel value
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5 Bitplane 5 pixel value
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6 Bitplane 6 pixel value
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7 Bitplane 7 pixel value /
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(EXTBG mode - Priority value)
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The data is then stored in the sequence
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00,01,02,03,04,05,06,07
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10,11,12,13,14,15,16,16 (Look at diagram at start of file
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| | | for explanation)
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70,71,72,73,74,75,76,77
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with one byte for each position(pixel), according to the 8x8 tile format,
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with one tile after another.
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---------------------------------------------------------------------------
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I hope this text file helps those of you having trouble converting graphics
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for use on the SNES, I have been asked a few times recently for this info
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so I decided to type up this short text file on it.
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Hopefully it should explain it!
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If you have any further questions contact :-
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Dax or Corsair
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