NES 2.0 Mapper 324: Difference between revisions
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(bus conflicts, mapper 72 is similar) |
(→Bank Register ($8000-$FFFF, write): reiterate what k is doing) |
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|||| +---- 1=Lock Outer Bank | |||| +---- 1=Lock Outer Bank | ||
|+++------ Select 128 KiB outer PRG-ROM bank | |+++------ Select 128 KiB outer PRG-ROM bank | ||
+--------- Clock Generator ("oook" bits latched only when this changes from 0 to 1) | +--------- Clock Generator ("oook" bits latched only when this changes from 0 to 1 if k had been 0) | ||
The middle four bits ($78, lowercase) are one 74'161; their contents are explicitly zeroed on power-up or reset. | The middle four bits ($78, lowercase) are one 74'161; their contents are explicitly zeroed on power-up or reset. | ||
Revision as of 00:16, 9 July 2018
NES 2.0 Mapper 324 is used for Farid's homebrew 8-in-1 UNROM multicart board. It consists of an UNROM latch with an additional outer bank register. Mirroring is hard-wired. Its UNIF board name is FARID_UNROM_8-IN-1.
Bank Register ($8000-$FFFF, write)
Mask: $8000
D~7654 3210 **BUS CONFLICTS**
---------
Cooo kIII
|||| ||||
|||| |+++- Standard UNROM inner bank (select 16K at $8000-$BFFF)
|||| +---- 1=Lock Outer Bank
|+++------ Select 128 KiB outer PRG-ROM bank
+--------- Clock Generator ("oook" bits latched only when this changes from 0 to 1 if k had been 0)
The middle four bits ($78, lowercase) are one 74'161; their contents are explicitly zeroed on power-up or reset. The outer four bits ($87, uppercase) are the other 74'161; their contents are NOT.
UNROM latch ($8000-$FFFF)
See INES Mapper 002.
See also
- NesDev discussion
- Mapper 72 uses a similar "one latch's output clocks another latch" structure.
