INES Mapper 038: Difference between revisions
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m (cat:GNROM) |
m (consistent naming...) |
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C = Selects 8kB CHR @ $0000 | C = Selects 8kB CHR @ $0000 | ||
Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The [[74138]] used by this board uses /PRGSEL and R/W on its enable inputs, but / | Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The [[74138]] used by this board uses /PRGSEL and R/W on its enable inputs, but /PRGSEL is 1 while M2 is low, not just while M2 and A15 are high. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the [[74161]]'s /LOAD line will still load from the data bus. | ||
Emulator oversize support: | Emulator oversize support: | ||
Revision as of 00:25, 2 July 2012
Mapper 38 represents another mapper very similiar to GNROM (66) except the bits and writeable port moved around.
In Disch's style:
$7000-$7FFF: [.... CCPP] P = Selects 32kB PRG @ $8000 C = Selects 8kB CHR @ $0000
Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The 74138 used by this board uses /PRGSEL and R/W on its enable inputs, but /PRGSEL is 1 while M2 is low, not just while M2 and A15 are high. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the 74161's /LOAD line will still load from the data bus.
Emulator oversize support:
FCEUX (2.1.5):
$7000-$7FFF: [CCCC CCPP]
Nestopia (1.4.0h):
$6000-$7FFF: [CCCC CC..]
[PPPP PPPP]
