INES Mapper 174: Difference between revisions
From NESdev Wiki
Jump to navigationJump to search
(notes on the $4025 and $4028 writes) |
m (text wrapping) |
||
| Line 50: | Line 50: | ||
the games (Urban Champion) writes to $4025. The purpose of these writes | the games (Urban Champion) writes to $4025. The purpose of these writes | ||
is unknown, as the cartridge does not trap those writes, and there is | is unknown, as the cartridge does not trap those writes, and there is | ||
(probably) no hardware in the NTDec famiclone that responds at those | (probably) no hardware in the NTDec famiclone that responds at those addresses. | ||
It can be noted though, that $4025 is the [[FDS]] motor control register, | It can be noted though, that $4025 is the [[FDS]] motor control register, | ||
and the value written would safely stop a disk system motor. | and the value written would safely stop a disk system motor. | ||
Revision as of 11:10, 3 July 2012
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:
---------------------------
$8000-FFFF: A~[.... .... OPPP CCCM]
M = Mirroring (1=Horizontal, 0=Vertical)
P = when O=0 selects 16k both @ $8000 and @ $C000
when O=1, the top two bits select 32k @ $8000 and the bottom bit is ignored
O = PRG mode: selects 16 kB (when 0) or 32 kB mode (when 1).
C = Selects 8 kB page for CHR memory $0000
All of the mapper register access seems to be done in $FF00-$FFFF range, however the entire range works.
The cartridge powers on in a state where all registers are 0.
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 power cycle the console (cold reboot).
This mapper is functionally identical to mapper 58 except the bits are moved around.
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 $4028 once in a while, and one of
the games (Urban Champion) writes to $4025. The purpose of these writes
is unknown, as the cartridge does not trap those writes, and there is
(probably) no hardware in the NTDec famiclone that responds at those addresses.
It can be noted though, that $4025 is the FDS motor control register,
and the value written would safely stop a disk system motor.
It is possibly a leftover from porting the game or its library routines
from the FDS to the Famicom. It does not explain the write to $4028 though.
More information: [1]
