I-RAM is the SA-1 internal memory. 2 kB (2048 bytes) big, it's clocked at 10.74 MHz and can be accessed though addresses $3000-$37FF on the S-CPU and $0000-$07FF or $3000-$37FF on the C-CPU
though banks $00-$3F and $80-$BF.
Being the fastest memory available, it's used mainly to hold the SMW's Direct Page,
as cache/scratch memory, some sprite tables as well C-CPU's stack and
Character Conversion DMA buffer.
The I-RAM has unrestricted memory access. C-CPU always accesses it at 10.74 MHz and S-CPU accesses at 2.68 MHz. The memory also offers write protection, useful for preventing data loss in case of a game crash. See SA-1 registers $2229 and $222A for more information.
Page in this document refers to a block of 0x100 or 256 bytes.
| Start |
End |
Description |
$3000 |
$30FF |
SMW's$7E:0000-$7E:00FF-- the Direct Page. |
| Start |
End |
Description |
$3100 |
$313F |
Extended scratch memory for the SA-1. Sometimes$00-$07is used in part of the boost patches, for sharing information between C-CPU and S-CPU. |
$3140 |
$317E |
Empty. Cleared on reset. |
$317F |
- |
Total character conversions to be done during NMI. If non-zero, the CC-DMA is executed on the next V-Blank period. |
$3180 |
$3182 |
SA-1 Code Pointer (from S-CPU to C-CPU). |
$3183 |
$3185 |
SNES Code Pointer (from C-CPU to S-CPU). |
$3186 |
$3188 |
SA-1 Parallel Mode Pointer. |
$3189 |
- |
SA-1 done flag (sets when the code pointed at $3080-$3082returns). |
$318A |
- |
SNES done flag (sets when the code pointed at $3083-$3085returns). |
$318B |
- |
Parallel Mode flag (set to start SA-1 Parallel Mode). |
$318C |
- |
SA-1 DMA done flag (sets when finished). |
$318D |
- |
Character Conversion DMA flag (sets when enabled). |
$318E |
- |
Special Flags (zw------) - w: Sets to 1 when the emulator (usually Snes9x) swaps the lower and upper part of a 6 or 8MB ROM, altering the behavior of the Super MMC registers
$2220-$2223. - z: ZSNES flag, which is used by certain parts of the patch to correct eventual emulator-specific issues.
|
$318F |
- |
Copy of the register$2225. If you change$2225, make sure to change this too. It's used to preserve the register value on SA-1 IRQs. |
$3190 |
$31DF |
Character Conversion DMA table. The table is 80 bytes long and allows up to 10 slots. See also $317F. |
$31E0 |
$31FF |
Memory reserved and dedicated for the Parallel Mode. |
| Start |
End |
Description |
$3200 |
$3215 |
SMW's$7E:009E (used to be Direct Page) |
$3216 |
$322B |
SMW's$7E:00D8 (used to be Direct Page) |
$322C |
$3241 |
SMW's$7E:00E4 (used to be Direct Page) |
$3242 |
$3257 |
SMW's$7E:14C8 |
$3258 |
$326D |
SMW's$7E:14D4 |
$326E |
$3283 |
SMW's$7E:14E0 |
$3284 |
$3299 |
SMW's$7E:151C |
$329A |
$32AF |
SMW's$7E:1528 |
$32B0 |
$32C5 |
SMW's$7E:1534 |
$32C6 |
$32DB |
SMW's$7E:1540 |
$32DC |
$32F1 |
SMW's$7E:154C |
$32F2 |
$3307 |
SMW's$7E:1558 |
| Start |
End |
Description |
$3308 |
$331D |
SMW's$7E:1564 |
$331E |
$3333 |
SMW's$7E:1570 |
$3334 |
$3349 |
SMW's$7E:157C |
$334A |
$335F |
SMW's$7E:1588 |
$3360 |
$3375 |
SMW's$7E:1594 |
$3376 |
$338B |
SMW's$7E:15A0 |
$338C |
$33A1 |
SMW's$7E:15AC |
$33A2 |
$33B7 |
SMW's$7E:15EA |
$33B8 |
$33CD |
SMW's$7E:15F6 |
$33CE |
$33E3 |
SMW's$7E:1602 |
$33E4 |
$33F9 |
SMW's$7E:160E |
$33FA |
$340F |
SMW's$7E:163E |
| Start |
End |
Description |
$3410 |
$3425 |
SMW's$7E:187B |
$3426 |
$34FF |
Empty. Cleared on reset. |
| Start |
End |
Description |
$3500 |
$35FF |
Empty. Cleared on reset. |
| Start |
End |
Description |
$3600 |
$36FF |
Empty. Cleared on reset. |
| Start |
End |
Description |
$3700 |
$377F |
Character Conversion output. This memory region is used by the hardware either as a buffer during the Character Conversion 1 DMA operation or as the character output during the Character Conversion 2 operation. Uses 32 bytes for 2BPP mode, 64 bytes for 4BPP mode and 128 bytes for 8BPP mode. See the SNES development book II, Section 1, Chapter 6 for more information. |
$3780 |
$37FF |
Reserved for the SA-1 CPU stack. |