INES Mapper 237
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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:
00 - 128 KiB UNROM 40 - defective interaction; UNROM but the lsb of the latch is ignored and treated as 0 80 - 16 KiB NROM (PRG A14 is connected to lsb of latch) C0 - 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.
See also:
