NES 2.0 Mapper 434 denotes the S-009 PCB, used by multicarts consisting of several UNROM games.
Mask: $E000
D~7654 3210
---------
..M. .PPP
| +++- PRG A19..A17
+------- 0: Horizontal mirroring
1: Vertical mirroring
Mask: $8000
D~7654 3210 (bus conflicts)
---------
.... .PPP
+++- PRG A16..A14 if CPU A14=0
Categories: Mappers with CHR RAM, Multicart mappers