Notes about the Nintendo Entertainment System
prefixed with a %
prefixed with a $
The CPU is a modified 6502. Has a 16-bit address bus. That means 2^16 bytes of mem. 16-bit digits are 4 hex digits.
- internal RAM is at $0000-0800 ($0800 = 2048 or 2KB)
- PPU IO Ports is at $2000-$4000
- APU/Conroller IO Ports $4000-$6000
- 8KB Cartridge RAM (WRAM) $6000-$8000
- 32KB Cartridge ROM $8000-$FFFA
- NMI/Reset/IRQ vectors $FFFF
The PPU is a custom chip that does graphics display.
- 4KB Cartridge RAM/ROM - Pattern Table 0 - 256 tiles - $0000-$1000
- 4KB Cartridge RAM/ROM - Pattern Table 1 - 256 tiles - $1000-$2000
- Name Table 0 - 32x30 tiles - $2000-$23C0
- Attribute Table 0 - $23C0-$2400
- Name Table 1 - 32x30 tiles - $2400-$27C0
- Attribute Table 1 - $27C0-$2800
- Name Table 2 - 32x30 tiles - $2800-$2BC0
- Attribute Table 2 - $2BC0-$2C00
- Name Table 3 - 32x30 tiles - $2C00-$2FC0
- Attribute Table 3 - $2FC0-$3000
- Background Palette - $3F00-$3F10
- Sprite Palette - $3F10-$3F20
All graphics are made up of 8x8 tiles.
The PPU can hold 64 sprites in memory. 8 sprites per scanlines are allowed.
These are commands for the assembler.
Start with . and are indented.
All registers are 8-bit.
-
A the accumulator
-
X the index register
-
Y another index register
lda for example will load into the A register.
lda #$20 will load A with 20 in hex. # means immediate value, not a address in memory, and $ means hex. % means binary. Nothing just means plain old decimal.
sta will store whatever is in the A register into memory.
Banks are where data goes.
Where the code goes. It starts at $8000.
Inturrupt table. Starts at $FFFA.
Sprite and background data. Starts at $0000.
How many code banks there are.
How many picture banks there are.