INES Mapper 237

iNES Mapper 237 represents the Teletubbies 420-in-1 multicart.

No bus conflicts on writes:

       address           data
 15 12   8    4    0  7  bit  0
 ---- ---- ---- ----  ---- ----
 1... .... .... .BLT  mtMB Bbbb
                 |||  |||| ||||
                 |||  |||| |+++-- inner 16 KiB bank
                 +-------+-+----- outer 128 KiB bank
                  ||  ||+-------- mirroring (0:horizontal/A11  1:vertical/A10)
                  ||  |+--------- transparency (0:PRG A14 is connected to lsb of latch  1:PRG A14 is connected to CPU A14 )
                  ||  +---------- mode (0:UNROM-PRG A14..A16 is bbb ORed with CPU A14  1:NROM-PRG A14..A16 is bbb )
                  |+------------- type (0:normal execution  1:PRG A1 is always 1 so CPU must execute from RAM)
                  +-------------- lock (0:allow further writes  1:only writes to bbb are allowed

The mt bits interact, so it might be more convenient to think of them together:

mt	$8000	$C000	in words
00	<BBBbbb>	<BBB111>	128 KiB UNROM
40	<BBBbb0>	<BBB111>	defective interaction; UNROM but the lsb of the latch is ignored and treated as 0
80	<BBBbbb>	<BBBbbb>	16 KiB NROM (PRG A14 is connected to lsb of latch)
C0	<BBBbb0>	<BBBbb1>	32 KiB NROM (PRG A14 is connected to CPU A14)

Note: the "type" bit probably depends on the specific cartridge. Implementing this differently will produce a different-seeming multicart. The software pretends that setting the Type bit replaces the entire ROM with a byte that specifies the kind of multicart present.

The L, T, m, and B bits are cleared on all resets. The others (t, M, and b) may be also.

See also:

• http://forums.nesdev.org/viewtopic.php?f=3&t=5977
• http://bootgod.dyndns.org:7777/downloads/420IN1.TXT