Mega Duck / Cougar Boy Console Info

April 24, 2026 · View on GitHub

A collection of technical information and resources for the Mega Duck console brought together in one place. Much of it researched by others, some by me (minor sound reg fixes, laptop model docs, some ports and patches, etc).

Web version

References

Credits / Thanks

Sean Riddle, Ruud van Falier, Nitro2k, Toxa, Youkal3, Zwenergy, Inside Gadgets, Kuddel, ManCloud

Software

Homebrew Games / Programs

ROM Patches

Patches for running Game Boy games on the MegaDuck

Homebrew Music Tools

Emulators/FPGA Re-implementations

Development Tools

C language
ASM
  • hardware.inc for MegaDuck: Hardware constants and addresses for use with asm/RGBDS
  • Asm83 - An Assembler, linker and librarian for retro CPUs including the sm83 (MegaDuck, Game Boy)

Music / SFX

Peripherals

  • Sample code for interfacing with the MegaDuck Laptop model Keyboard, RTC and speech module (Quique and Junior Computer). See related partial docs
  • Audio recordings of the 6 built-in speech phrases for the German and Spanish MegaDuck Laptop models

Hardware

Flash Cartridges

Hardware Schematics / PCB Info

Adapters

Display mod / LCD Header info

Laptop model Gamepad

  • The link port on the Mega Duck has the same pin order and signals as the Game Boy, but a different connector style (bare header).
  • The serial control registers have the same address, control flags and behavior as a the Game Boy

With the use of a connector style adapter a Mega Duck and a Game Boy can exchange data over their link ports.

Diagram showing the link port receptacle*1 pinout when looking at the side of the console:

      Front of console
-----------------------------------
                                   |
--------      -----------------    |
 volume |    | CLK  SIN  VCC*2 |   |
 dial   |    | GND   -   SOUT  |   |
--------      -----------------    |
                                   |
-----------------------------------                                   
       Back of console
  • 1: View and pinout is of the connector receptacle, not of the cable
  • 2: For most uses the VCC pin should not be connected

Cartridge Pinout

AC Adapters

Handheld

  • 3.5 mm exterior, 1.35mm interior
  • 6 volts, centrer NEGATIVE polarity

Laptop

  • 3.5 mm exterior, 1.35mm interior
  • 9 volts, centrer POSITIVE polarity
  • Example picture

USB Video Streaming

MBCs / Bank Switching

MBC Controllers

Laptop model System ROM MBC (CEFA Super Quique, Hartung Super Junior Computer):

  • Informal MBC Number: 0xE0 (SuperJuniorSameDuck emulator)
  • Informal extension: .md0
  • Register: 0x1000
    • ROM Bank
      • Selected by writing (0 - 15) in Lower Nibble (mask 0x0F)
      • Bank Size/Region: Switches the full 32K ROM region-
    • SRAM Bank (on secondary memory cart plugged into memory cart slot)
      • Selected by writing (0 - 3) in Upper Nibble (mask 0x30)
      • Bank Size/Region: 8k mapped at 0xA000 - 0xBFFF
  • Laptop Games: MegaDuck_Laptop_BilderLexikon.md0, MegaDuck_Laptop_DataBank.md0 (requires SRAM cart)
  • System ROMs: MegaDuck_Laptop_SystemROM_German.md0, MegaDuck_Laptop_SystemROM_Spanish.md0
  • Note: Uses a delay of ~41 M-Cycles (executed from WRAM) after writing the bank switch before resuming execution from ROM. Unclear if required.

OEM Games:

  • 32K with NO switchable banks
    • Sometimes with extension: .bin, but that may also be used for banked ROMs with some emulators
    • Handheld Games: Arctic Zone, Bomb Disposer, Magic Maze, Pile Wonder, Street Rider, The Brick Wall, Trap and Turn, Vex
  • 32K switchable banks
    • Sometimes with extension: .md1
    • Informal MBC Number: 0xE1 (SuperJuniorSameDuck emulator)
    • Register: Bank selected by writing 0 - 1 to 0xB000
    • Bank Size/Region: Switches the full 32K ROM region
    • Handheld Games: Puppet Knight, Suleiman’s Treasure
  • Upper switchable 16K banks
    • Sometimes with extension: .md2
    • Informal MBC Number: 0xE2 (SuperJuniorSameDuck emulator)
    • Register: Bank selected by writing 1 - 3 or 1-7 to 0x0001 depending on total ROM size (64K or 128K)
    • Bank Size/Region: 16K in the Upper ROM region 0x4000 - 0x7FFF (lower 16K at 0x0000 - 0x3FFF is fixed bank 0)
    • Laptop Games: MegaDuck_Laptop_MusikModul.md2
    • Handheld Games: 2nd Space, Ant Soldiers, Armour Force, Beast Fighter, Black Forest Tale, Captain Knick Knack, Commin Five in One, Duck Adventures, Four in One, Magic Tower, Railway, Snake Roy, Worm Visitor, Zipball

MBC type per game is according to Reddit

Implementation in emulators

Game Boy ROMs contain an embedded meta-data header which (usually) indicates the type of MBC (Memory Bank Controller) used. This allows emulators to automatically emulate the correct cart hardware (the Game Boy hardware itself ignores this and doesn't need it since the cart hardware is present).

OEM Mega Duck ROMs lack this header which means that emulators have to use other methods to infer what type of cart MBC is required by a given ROM.

The main methods for selecting the right MegaDuck cart MBC:

  • By File Extension (.md1 = 32K banks, .md2 = Upper 16K Banks, .bin = 32k no mbc)
    • Analogue Pocket OpenFPGA MegaDuck Core
  • By hashes of the ROMs
    • MAME (partially)
  • By emulating both MBC styles at the same time in case a game uses either. This works since the two MBCs use a different register address.
    • MAME (partially), MiSTer

System ROMs

Porting from Game Boy to Mega Duck

Developing for the Mega Duck is mostly identical (cpu & integrated peripherals) to the Original Game Boy though it has a couple changes listed below.

Register and flag names will mostly follow those in the Game Boy dev hardware.inc, but may have some GBDK-isms.

Most of this research was done by others, I've added a small amount.

Summary of Hardware changes versus the Game Boy:

Physical / Hardware:

  • Different cartridge pinout / connector
  • Different serial link port connector shape

Programming:

  • No Boot ROM
  • Cartridge Boot Logo: not present on Mega Duck
  • Cartridge Header data: not present on Mega Duck
    • Checksum header: not present on Mega Duck. Do not apply checksum to ROM after building as on the Game Boy
  • Program Entry Point: 0x0000 (on Game Boy: 0x0100 )
  • Initial registers
    • Handheld Models: (AF, BC, DE, HL, SP) are random at startup (due to lack of boot rom) with some affinity toward 0xFFFF / 0x0000
    • Laptop Model: Based on System ROM design (no stack init before first call/ret) it appears SP is NOT 0x0000 at power-on
      • Possibly it's something like 0xFFFE or lower which would allow pushing and popping the stack before init without a resulting crash
  • Serial control
    • Laptop Mode: Based on System ROM design and behavior it seems possible to use SC and SB reg outside normal GB guidelines (Sending still works when triggering SC to send before loading the send value into SB).
  • Display registers address and flag definitions: Some changed (details below)
  • VRAM data:
    • The user program should clear it before use.
    • For Handhelds: since a boot ROM does not run on startup it means Tile Map and Pattern data are not cleared and will have (consistent) random data.
    • For Laptop models: The System ROM will not clear VRAM before launching a user program from the system menu. The font patterns left in VRAM on program startup can be used to tell the difference between the Super Quique (Spanish) and Super Junior (German) laptop models. See example code.
  • Audio registers address and flag definitions: Some changed (details below)
  • Different MBC bank switching register addresses than Game Boy MBCs

Laptop:

  • Built-in System ROM
  • Additional Cart Slot for add-on Memory Card (access not yet documented)
  • Peripherals attached via Serial/Link port
    • Keyboard + Piano Keys
    • RTC
    • Cart
    • Detached Gamepad
    • Mechanism to launch cartridges in the Cart Slot
    • External communication port for the printer (type not yet documented)

Sound Register Value/Data Changes

These changes should be kept in mind when porting Sound Effects and Music Drivers written for the Game Boy.

  1. Registers NR12, NR22, NR42, and NR43 have their contents nybble swapped.
    • To maintain compatibility with the Game Boy the value to write (or the value read) can be converted this way: ((uint8_t)(value << 4) | (uint8_t)(value >> 4))
  2. Register NR32 has the volume bit values changed.
    • Game Boy: Bits:6..5 : 00 = mute, 01 = 100%, 10 = 50%, 11 = 25%
    • Mega Duck: Bits:6..5 : 00 = mute, 01 = 25%, 10 = 50%, 11 = 100%
    • To maintain compatibility witht he Game Boy the value to write (or the value read) can be converted this way: (((~(uint8_t)value) + (uint8_t)0x20u) & (uint8_t)0x60u)

Sound Register Changes Table

  • Addr Change means deviation from the expected linear incrementing register address order per sound channel that the Game Boy registers follow. The shuffled order on the Mega Duck can break assumptions in Game Boy sound drivers which attempt to write each channel as a sequential block using an incrementing register pointer.
RegAlt NameGame BoyMega DuckData ChangeAddr Change
NR10rAUD1SWEEP0xFF100xFF20
NR11rAUD1LEN0xFF110xFF22Addr +1
NR12rAUD1ENV0xFF120xFF21nybble swapAddr -1
NR13rAUD1LOW0xFF130xFF23
NR14rAUD1HIGH0xFF140xFF24
NR21rAUD2LEN0xFF160xFF25Addr -1
NR22rAUD2ENV0xFF170xFF27nybble swap
NR23rAUD2LOW0xFF180xFF28
NR24rAUD2HIGH0xFF190xFF29
NR30rAUD3ENA0xFF1A0xFF2A
NR31rAUD3LEN0xFF1B0xFF2B
NR32rAUD3LEVEL0xFF1C0xFF2Cvolume bit swizzle
NR33rAUD3LOW0xFF1D0xFF2EAddr +1
NR34rAUD3HIGH0xFF1E0xFF2DAddr -1
NR41rAUD4LEN0xFF200xFF40
NR42rAUD4ENV0xFF210xFF42nybble swapAddr +1
NR43rAUD4POLY0xFF220xFF41nybble swapAddr -1
NR44rAUD4GO0xFF230xFF43
NR50rAUDVOL0xFF240xFF44
NR51rAUDTERM0xFF250xFF46Addr +1
NR52rAUDENA0xFF260xFF45Addr +1

Graphics Register Bit Flag Changes

LCDC FlagGame BoyMega DuckPurpose
LCDCF_B_ON.7.7(same)Bit for LCD On/Off Select
LCDCF_B_WIN9C00.6.3Bit for Window Tile Map Region Select
LCDCF_B_WINON.5.5(same)Bit for Window Display On/Off Control
LCDCF_B_BG8000.4.4(same)Bit for BG & Window Tile Data Region Select
LCDCF_B_BG9C00.3.2Bit for BG Tile Map Region Select
LCDCF_B_OBJ16.2.1Bit for Sprites Size Select
LCDCF_B_OBJON.1.0Bit for Sprites Display Visible/Hidden Select
LCDCF_B_BGON.0.6Bit for Background Display Visible Hidden Select

Graphics Register Address Changes

RegisterGame BoyMega Duck
LCDC0xFF400xFF10
STAT0xFF410xFF11
SCY0xFF420xFF12
SCX0xFF430xFF13
LY0xFF440xFF18
LYC0xFF450xFF19
DMA0xFF460xFF1A
BGP0xFF470xFF1B
OBP00xFF480xFF14
OBP10xFF490xFF15
WY0xFF4A0xFF16
WX0xFF4B0xFF17