ROM header
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Every WonderSwan ROM contains a header. It is stored at the end - final sixteen bytes - of the ROM image.
ROM header
Parts of this header are validated or otherwise used by the console's boot ROM - they are marked in bold.
| Offset | Length | Contents |
|---|---|---|
| $0 | 5 | Far jump instruction: 0xEA, offset, segment. |
| $5 | 1 | Maintenance |
| $6 | 1 | Developer/Publisher ID |
| $7 | 1 | Color |
| $8 | 1 | Game ID (binary-coded decimal) |
| $9 | 1 | Game version? / Safe mode |
| $A | 1 | ROM size |
| $B | 1 | Save type/size |
| $C | 1 | Flags |
| $D | 1 | Mapper type |
| $E | 2 | Checksum (sum of all ROM bytes excluding the checksum) |
$5 - Maintenance
s...0000
| ++++- Must be zero; otherwise the console will prohibit execution.
| Purpose unknown.
+-------- (Color) Splash bypass: 0 = Disable, 1 = Enable.
Bypasses the custom boot splash stored in the console's
internal EEPROM; presumably used for bricked console recovery.
$6 - Developer/Publisher ID
| ID | Publisher |
|---|---|
| $01 | Bandai |
| $02 | Taito |
| $03 | ? |
| $04 | Koei |
| $05 | Data East |
| $06 | Asmik Ace |
| $07 | Media Entertainment |
| $08 | Nichibutsu |
| $0A | Coconuts Japan |
| $0B | Sammy |
| $0C | Sunsoft |
| $0D | ? |
| $0E | Banpresto |
| $10 | Jaleco |
| $11 | Imagineer |
| $12 | Konami |
| $16 | Kobunsha |
| $17 | Bottom Up |
| $18 | ? |
| $19 | Sunrise |
| $1A | Cyber Front |
| $1B | Megahouse |
| $1D | Interbec |
| $1E | ? |
| $1F | ? |
| $20 | Athena |
| $21 | KID |
| $22 | ? |
| $23 | ? |
| $24 | Omega Micott |
| $25 | ? |
| $26 | ? |
| $27 | ? |
| $28 | Squaresoft |
| $2A | ? |
| $2B | ? |
| $2D | Namco |
| $2E | ? |
| $2F | ? |
| $31 | ? |
| $32 | ? |
| $33 | ? |
| $36 | ? |
Note that IDs $00 and $01 are used across a variety of commercial games. Homebrew is known to use arbitrary values in this field.
$7 - Color
???????c
+- 0 = Monochrome only, 1 = Supports Color mode.
$9 - Game version? / Safe mode
pvvvvvvv
|+++++++- Game version?
+-------- Internal EEPROM write protect: 0 = Enable, 1 = Disable.
This prohibits writing to the internal EEPROM for addresses
0x60 and above (user settings, custom splash screen).
Games are expected to enable write protection; however, the
WonderWitch is factory configured with it disabled.
$A - ROM size
Unofficial ROM size values are marked in italic.
| ID | Size |
|---|---|
| $00 | 1 Mbit (128 KiB) |
| $01 | 2 Mbit (256 KiB) |
| $02 | 4 Mbit (512 KiB) |
| $03 | 8 Mbit (1 MiB) |
| $04 | 16 Mbit (2 MiB) |
| $05 | 24 Mbit (3 MiB) |
| $06 | 32 Mbit (4 MiB) |
| $07 | 48 Mbit (6 MiB) |
| $08 | 64 Mbit (8 MiB) |
| $09 | 128 Mbit (16 MiB) |
| $0A | 256 Mbit (32 MiB)[1] |
| $0B | 512 Mbit (64 MiB)[1] |
$B - Save type/size
| ID | Type | Size |
|---|---|---|
| $00 | None | |
| $01 | SRAM | 64 Kbit (8 KiB) |
| $02 | 256 Kbit (32 KiB) | |
| $03 | 1 Mbit (128 KiB) | |
| $04 | 2 Mbit (256 KiB) | |
| $05 | 4 Mbit (512 KiB) | |
| $10 | EEPROM | 1 Kbit (128 B) |
| $20 | 16 Kbit (2 KiB) | |
| $50 | 8 Kbit (1 KiB) | |
$C - Flags
?????SBv
||+- Starting screen orientation: 0 = Horizontal, 1 = Vertical.
|| Controls the splash screen's orientation.
|+-- ROM bus width: 0 = 16-bit, 1 = 8-bit.
+--- ROM access time: 0 = 3 CPU cycles, 1 = 1 CPU cycle.
$D - Mapper type
| ID | Mapper |
|---|---|
| $00 | Bandai 2001 |
| $01 | Bandai 2003 |
| $02 | KARNAK (Pocket Challenge V2) |
- ↑ 1.0 1.1 Not supported by the Bandai 2001 mapper, which is limited to 16 MiB. The Bandai 2003 mapper is limited to 64 MiB.
