PPU pattern tables: Difference between revisions
(clarified left and right display in debuggers) |
(added pattern table address decode) |
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=Overview= | |||
Backgrounds and sprites are drawn with tiles. | Backgrounds and sprites are drawn with tiles. | ||
The pattern table, at $0000-$1FFF in PPU address space, defines the shapes of these tiles. | The pattern table, at $0000-$1FFF in PPU address space, defines the shapes of these tiles. | ||
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The nicknames come from how emulators with a debugger display the pattern table. | The nicknames come from how emulators with a debugger display the pattern table. | ||
Traditionally, they are displayed as two side-by-side 128x128 pixel sections, each representing 16x16 tiles from the pattern table, with $0000-$0FFF on the left and $1000-$1FFF on the right. | Traditionally, they are displayed as two side-by-side 128x128 pixel sections, each representing 16x16 tiles from the pattern table, with $0000-$0FFF on the left and $1000-$1FFF on the right. | ||
=Addressing= | |||
For a given 12-bit address in the pattern table, the address can be decoded as follows: | |||
CBA9876543210 (high order bits first) | |||
------------- | |||
HRRRRCCCCPTTT | |||
Where the letters mean: | |||
#. H - Hand (0 = "left", 1 = "right") | |||
#. R - Tile row | |||
#. C - Tile column | |||
#. P - Bit plane (0 = "lower", 1 = "upper") | |||
#. T - Fine Y offset (i.e. the row number of a given 16x16 tile) | |||
Revision as of 20:09, 3 March 2015
Overview
Backgrounds and sprites are drawn with tiles. The pattern table, at $0000-$1FFF in PPU address space, defines the shapes of these tiles. Each tile in the pattern table is 16 bytes, made of two planes. The first plane controls bit 0 of the color; the second plane controls bit 1. Any pixel whose color is 0 is background/transparent (represented by '.' in the following diagram):
Bit Planes Pixel Pattern
$0xx0=$41 01000001
$0xx1=$C2 11000010
$0xx2=$44 01000100
$0xx3=$48 01001000
$0xx4=$10 00010000
$0xx5=$20 00100000 .1.....3
$0xx6=$40 01000000 11....3.
$0xx7=$80 10000000 ===== .1...3..
.1..3...
$0xx8=$01 00000001 ===== ...3.22.
$0xx9=$02 00000010 ..3....2
$0xxA=$04 00000100 .3....2.
$0xxB=$08 00001000 3....222
$0xxC=$16 00010110
$0xxD=$21 00100001
$0xxE=$42 01000010
$0xxF=$87 10000111
The pattern table is divided into two 256-tile sections: $0000-$0FFF, nicknamed "left", and $1000-$1FFF, nicknamed "right". The nicknames come from how emulators with a debugger display the pattern table. Traditionally, they are displayed as two side-by-side 128x128 pixel sections, each representing 16x16 tiles from the pattern table, with $0000-$0FFF on the left and $1000-$1FFF on the right.
Addressing
For a given 12-bit address in the pattern table, the address can be decoded as follows:
CBA9876543210 (high order bits first) ------------- HRRRRCCCCPTTT
Where the letters mean:
- . H - Hand (0 = "left", 1 = "right")
- . R - Tile row
- . C - Tile column
- . P - Bit plane (0 = "lower", 1 = "upper")
- . T - Fine Y offset (i.e. the row number of a given 16x16 tile)
