On original hardware, writes to OAMADDR cause the values at the 8-byte block of OAM previously pointed to to be written to a non-random location. Additionally, a value in OAMADDR greater than 7 will cause that 8-byte chunk to be written to the start of OAM. This corruption must be emulated to ensure full compatibility.
More details on this corruption behaviour can be found here.
On original hardware, writes to OAMADDR cause the values at the 8-byte block of OAM previously pointed to to be written to a non-random location. Additionally, a value in OAMADDR greater than 7 will cause that 8-byte chunk to be written to the start of OAM. This corruption must be emulated to ensure full compatibility.
More details on this corruption behaviour can be found here.