The PPU can render up to 64 sprites.
• 8x8 Mode: This selects a tile in the pattern table from 0-255, or if bit 3 of PPU_CTRL is set, a tile from 256-511.
• 8x16 Mode: Two consecutive tiles are selected, the first for the top half and the second for the bottom half.
The sprite data is held in 256 bytes of RAM inside the PPU called OAM (Object Attribute Memory).
The PPU can fill OAM by reading directly from the CPU’s RAM, usually once per video frame.