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Mother 3/SRAM map

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This is the SRAM map for MOTHER 3. A MOTHER 3 save file contains data for two file slots. This page will follow the convention of using $ as a prefix for addresses, and 0x as a prefix for values.

Overview

The SRAM is divided into 16 banks of 0x1000 bytes each. All banks that are in use begin with the 4-byte header 

02 00 4D 33

This is convenient, since we can seed the checksum with a value of 0x334F and begin summing at the spot after the checksum, rather than having to manually skip over the checksum bytes.

Checksums

Each bank that's in use has a 16-bit checksum complement at the 4th and 5th byte. There's an exception for bank 0: this checksum is located at $000F0 instead, and it only takes into account the data stored from $00000 to $000EF.

The checksum is calculated by summing each 16-bit value in the bank (not including the checksum itself), and the complementing it with 0xFFFF. For example, if the bank started with the bytes 

02 00 4D 33 xx xx 91 B7 3F 02 7C 0C ...

Then the checksum would start off by summing 

  0002
+ 334D
+ B791
+ 023F
+ 0C7C
+  ...

If any checksum is incorrect, the game will delete the entire save data.

Bank 0 (00000-00FFF)

This bank contains some general overhead data. It is mirrored at bank 1.

  • 00000-00003 (004) = Standard header
  • 00004-00015 (012) = Unclassified data
  • 00016-00019 (004) = Slot 1 current party. Must be in sync with the party bytes at $04008 in bank 4.
  • 0001A-00067 (04E) = Unclassified data
  • 00068-00068 (001) = Slot 1 flag. Zero if there is no save file in slot 1, non-zero otherwise
  • 00069-00079 (011) = Unclassified data
  • 0007A-0007D (004) = Slot 2 current party. Must be in sync with the party bytes at $0A008 in bank 10.
  • 0007E-000CB (04E) = Unclassified data
  • 000CC-000CC (001) = Slot 2 flag. Zero if there is no save file in slot 2, non-zero otherwise
  • 000CD-000CF (003) = Unclassified data
  • 000D0-000D7 (008) = "mother3 " in ASCII
  • 000D8-000EF (018) = Unclassified data
  • 000F0-000F1 (002) = Checksum complement
  • 000F2-00FFF (F0E) = Unused

Bank 1 (01000-01FFF)

Mirror of bank 0.

Banks 2 and 3 (02000-03FFF)

Unclassified; most likely unused, as they are filled with 0xFF, and are missing the standard header and checksum.

Bank 4 (04000-04FFF)

This bank contains the slot 1 data. It is mirrored at bank 7.

Key item flags

From $04018 to $04117, there are one-byte item flags corresponding to the player's key items. A value of zero means the player doesn't have the item; non-zero means they do have it. The exact values that these flags can hold is unknown; however, the game does seem to cap them at 99, so it's possible that it indicates how many of that item are being held.

Most of the values in this range do not correspond to key items and have no effect. Only items with an item type of 8 are considered.

These values follow the standard internal item order.

Item Guy's inventory

Item Guy is like an item bank. There are 256 bytes here, one for each item, again following the standard internal item order. Each byte represents the quantity of that item being carried by Item Guy.

Play time

The play time is stored in ticks. Each tick is 1/60th of a second; hence, where we use integer division instead of real division,

  • Hours = total ticks / 216000
  • Minutes = (total ticks / 3600) % 60
  • Seconds = (total ticks / 60) % 60
  • Tick remainder = total ticks % 60

PSI flags

Lucas and Kumatora each have 64 PSI flags, stored at $04728 and $04742, respectively. Each flag is one bit: 1 means the PSI has been learned, and 0 means it hasn't. It follows the game's internal PSI order.

It is important to note that the game will crash if more than 36 flags are set for either character, despite there being space for 64 flags.

Enemy-seen flags

Whenever you encounter an enemy and see its front-side in-battle, the game sets a flag in the $04752 area. Likewise, if you see the enemy's back, it sets a flag in the $04772 area. There is one bit per enemy, and the in-game enemy ordering is used. These flags are used when accessing the Battle Memory item.

Character data

Each block of character data uses 0x6C bytes and is mapped below.

  • 00-00 (01) = Character number (follows the game's internal party character naming order)
  • 01-01 (01) = Sprite number (follows the game's internal sprite listing)
  • 02-11 (10) = Name
  • 12-12 (01) = Level
  • 13-13 (01) = Unused
  • 14-17 (04) = Experience
  • 18-1B (04) = Current HP
  • 1C-1D (02) = Current PP
  • 1E-1F (02) = Unclassified data
  • 20-23 (04) = Maximum HP
  • 24-25 (02) = Maximum PP
  • 26-27 (02) = Unclassified data
  • 28-28 (01) = Offense
  • 29-29 (01) = Defense
  • 2A-2A (01) = IQ
  • 2B-2B (01) = Speed
  • 2C-33 (08) = Unclassified data
  • 34-34 (01) = Weapon (equipped)
  • 35-35 (01) = Body (equipped)
  • 36-36 (01) = Head (equipped)
  • 37-37 (01) = Other (equipped)
  • 38-3B (04) = Unclassified data (bitfield)
  • 3C-4B (10) = Inventory
  • 4C-6B (20) = Unclassified; occasionally, this will be the character's inventory stored as 16-bit values

Bank 5 (05000-05FFF)

Unclassified.

Bank 6 (06000-06FFF)

Unclassified. Contains some palette data starting at $06208.

Bank 7 (07000-07FFF)

Mirror of bank 4.

Bank 8 (08000-08FFF)

Mirror of bank 5.

Bank 9 (09000-09FFF)

Mirror of bank 6.

Bank 10 (0A000-0AFFF)

This bank contains the slot 2 data. It is mirrored at bank 13. It follows the exact same mapping as bank 4; just replace the $04xxx address prefix with $0Axxx.

Bank 11 (0B000-0BFFF)

Unclassified. Like bank 5, but not a mirror of it.

Bank 12 (0C000-0CFFF)

Unclassified. Like bank 6, but not a mirror of it.

Bank 13 (0D000-0DFFF)

Mirror of bank 10.

Bank 14 (0E000-0EFFF)

Mirror of bank 11.

Bank 15 (0F000-0FFFF)

Mirror of bank 12.

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