CPU memory map: Difference between revisions
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(Changing to range-and-size to match PPU memory map, esp. with note using ranges; changed grammar.) |
(Technically, a mapper *could* switch the vectors alone. Also, the vectors are parts of "usual ROM") |
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| Line 24: | Line 24: | ||
*$6000-$7FFF = Battery Backed Save or Work RAM | *$6000-$7FFF = Battery Backed Save or Work RAM | ||
*$8000-$ | *$8000-$FFFF = Usual ROM, commonly with Mapper Registers (see [[MMC1]] and [[UxROM]] for example) | ||
The CPU expects three addresses called "vectors" in fixed places at the end of the cartridge space, like so: | The CPU expects three addresses called "vectors" in fixed places at the end of the cartridge space, like so: | ||
| Line 32: | Line 32: | ||
*$FFFE-$FFFF = IRQ/BRK vector | *$FFFE-$FFFF = IRQ/BRK vector | ||
If a mapper doesn't fix $C000-$FFFF to the last bank or use some sort of reset detection, the vectors need to be stored in all banks. | If a mapper doesn't fix $C000-$FFFF to the last bank or use some sort of reset detection, the vectors need to be stored in all banks. | ||
Revision as of 07:52, 28 May 2015
| Address range | Size | Device |
|---|---|---|
| $0000-$07FF | $0800 | 2KB internal RAM |
| $0800-$0FFF | $0800 | Mirrors of $0000-$07FF |
| $1000-$17FF | $0800 | |
| $1800-$1FFF | $0800 | |
| $2000-$2007 | $0008 | NES PPU registers |
| $2008-$3FFF | $1FF8 | Mirrors of $2000-2007 (repeats every 8 bytes) |
| $4000-$401F | $0020 | NES APU and I/O registers |
| $4020-$FFFF | $BFE0 | Cartridge space: PRG ROM, PRG RAM, and mapper registers (See Note) |
See Sample RAM map for an example allocation strategy for the 2KB of internal RAM at $0000-$0800.
Note: Most common boards address ROM and Save/Work RAM in this format, especially in common iNES mappers:
- $6000-$7FFF = Battery Backed Save or Work RAM
- $8000-$FFFF = Usual ROM, commonly with Mapper Registers (see MMC1 and UxROM for example)
The CPU expects three addresses called "vectors" in fixed places at the end of the cartridge space, like so:
- $FFFA-$FFFB = NMI vector
- $FFFC-$FFFD = Reset vector
- $FFFE-$FFFF = IRQ/BRK vector
If a mapper doesn't fix $C000-$FFFF to the last bank or use some sort of reset detection, the vectors need to be stored in all banks.
