INES Mapper 174

 Here are Bisqwit's original notes:  
 ========================
 =  Mapper 252          =
 ========================
 
 Example Game:
 --------------------------
 NTDec 5-in-1 (PAL), Famicom cartridge format
 
 PRG ROM size: 128 kB
 CHR ROM size: 64 kB 
 
 Registers:
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  $8000-FFFF:     A~[.... .... HLLL CCCM]
     M = Mirroring (1=Horizontal, 0=Vertical)
     L = Selects 16 kB page for PRG memory $8000 as L*0x4000
     H = Selects 16 kB page for PRG memory $C000: If 1, selects L+0x4000, else selects same as L
     C = Selects 8 kB page for CHR memory $0000
 
 All of the mapper register access seems to be done in $FF00-$FFFF range.
 It is unknown what is the exact range of memory where writes are trapped.
 It is also unknown where exactly the PRG memory page $8000 is mapped when H=0,
 because when H=0, the games on the cartridge only access memory range $C000-$FFFF.
 Additionally, it is unknown what happens if H=1 and L&1 = 1, because none of
 the cartridge's code ever invokes that situation.
 
 The cartridge powers on in a state where L=0, H=0.
 (It is not known whether M, C are also 0 after poweron.)
 
 The cartridge expect the RAM contents to be kept when reset is pressed,
 whereupon it boots the game. The only way to return to the main menu after
 selecting a game is to powercycle the console (cold reboot).
 
 
 Notes:
 ---------------------------
 This mapper is probably unique to that board, constructed from
 two GD74LS161As (4-bit binary counter) and one GD74LS153 (dual 4-input multiplexer).
 
 It is a multicart that consists of games of different sizes.
 - Three games with PRG size = 32 kB (The Legend of Kage, The Goonies, Arkanoid)
 - One game with PRG size = 16 kB (Urban Champion)
 - One game with PRG size = 8 kB (Galaxian), which shares a 16 kB page together with the main menu.
 
 All the games have been edited to remove any copyright information from rendering
 (the ROM data still does contain some of the trademark and copyright strings).
 They also have been edited to access the cartridge's memory remapping I/O rather
 than the original mapper I/O of those respective games.
 
 The main menu also does some writes to $4025 once in a while, and one of
 the games (Urban Champion) writes to $4028. The purpose of these writes
 is unknown, as the cartridge does not trap those writes.

More information: http://nesdev.parodius.com/bbs/viewtopic.php?p=96276#96276