INES Mapper 209

iNES Mapper 209 refers to versions of the ASIC mapper used by JY Company where bit 5 of port $D000 switches between simple nametable control (like INES Mapper 090) and extended nametable control that allows mapping CHR ROM into nametables (like iNES Mapper 211).

Mapper 209 also seems to have a significantly different meaning to its 4K CHR banking mode (i.e. ([$D000]&$18) == $08), rather like an MMC4.

Using the terminology from MMC4:

$A000,$9000 - Select 4 KB CHR ROM bank for PPU $0000-$0FFF used when latch 0 = $FD
$A002,$9002 - Select 4 KB CHR ROM bank for PPU $0000-$0FFF used when latch 0 = $FE
$A004,$9004 - Select 4 KB CHR ROM bank for PPU $1000-$1FFF used when latch 1 = $FD
$A006,$9006 - Select 4 KB CHR ROM bank for PPU $1000-$1FFF used when latch 1 = $FE

See also: https://forums.nesdev.org/viewtopic.php?t=15333