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 |
| $E | 2 | Checksum (sum of all ROM bytes excluding the checksum) |
Maintenance ($5)
7 bit 0
---- ----
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.
Developer/Publisher ID ($6)
| ID | Publisher code | Publisher |
|---|---|---|
| $01 | BAN | Bandai |
| $02 | TAT | Taito |
| $03 | TMY | Tomy |
| $04 | KEX | Koei |
| $05 | DTE | Data East |
| $06 | AAE | Asmik Ace |
| $07 | MDE | Media Entertainment |
| $08 | NHB | Nichibutsu |
| $0A | CCJ | Coconuts Japan |
| $0B | SUM | Sammy |
| $0C | SUN | Sunsoft |
| $0D | PAW | Mebius |
| $0E | BPR | Banpresto |
| $10 | JLC | Jaleco |
| $11 | MGA | Imagineer |
| $12 | KNM | Konami |
| $16 | KBS | Kobunsha |
| $17 | BTM | Bottom Up |
| $18 | KGT | Kaga Tech |
| $19 | SRV | Sunrise |
| $1A | CFT | Cyber Front |
| $1B | MGH | Megahouse |
| $1D | BEC | Interbec |
| $1E | NAP | Nihon Application |
| $1F | BVL | Bandai Visual |
| $20 | ATN | Athena |
| $21 | KDX | KID |
| $22 | HAL | HAL Corporation |
| $23 | YKE | Yuki Enterprise |
| $24 | OMN | Omega Micott |
| $25 | LAY | Layup |
| $26 | KDK | Kadokawa Shoten |
| $27 | SHL | Shall Luck |
| $28 | SQR | Squaresoft |
| $2A | SCC | ? (SUNCORPORATION?) |
| $2B | TMC | Tom Create |
| $2D | NMC | Namco |
| $2E | SES | Soeishinsha |
| $2F | HTR | Hearty Robin |
| $31 | VGD | Vanguard |
| $32 | MGT | Megatron |
| $33 | WIZ | Wiz |
| $35 | TAN | Tanita |
| $36 | CPC | Capcom |
Note that IDs $00 and $01 are used across a variety of commercial games. Homebrew is known to use arbitrary values in this field.
Color ($7)
7 bit 0
---- ----
???? ???c
|
+- 0 = Monochrome only, 1 = Supports Color mode.
Game version? / Safe mode ($9)
7 bit 0
---- ----
pvvv vvvv
|||| ||||
|+++ ++++- Game version?
+--------- Internal EEPROM write protect: 0 = Enable, 1 = Disable.
This prohibits writing to the internal EEPROM for addresses
0x60 and above (user settings, custom splash screen).
Games are expected to enable write protection; however, the
WonderWitch is factory configured with it disabled.
ROM size ($A)
Unofficial/inferred 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) |
| $0B | 512 Mbit (64 MiB) |
Note that ROM sizes over 16 MiB are not supported by the Bandai 2001 mapper. The Bandai 2003 mapper is limited to 64 MiB.
Save type/size ($B)
| ID | Type | Size |
|---|---|---|
| $00 | None | |
| $01 | SRAM | 256 Kbit (32 KiB) |
| $02 | ||
| $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) | |
Note that while ID $01 is commonly documented as 64 Kbit, all known cartridges using that value come with 256 Kbit SRAM chips. This requires further investigation.
Flags ($C)
7 bit 0
---- ----
???? ?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.
Mapper ($D)
| ID | Mapper |
|---|---|
| $00 | Bandai 2001 or KARNAK |
| $01 | Bandai 2003 |
