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:
| 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:
