Sega - MS/GG/MD/CD (Genesis Plus GX)Link


Genesis Plus GX is an open-source Sega 8/16 bit emulator focused on accuracy and portability. The source code, originally based on Genesis Plus 1.3 by Charles MacDonald, has been heavily modified & enhanced, with respect to initial goals and design, in order to improve the accuracy of emulation, implementing new features and adding support for extra peripherals, cartridge & systems hardware.


The Genesis Plus GX core has been authored by

  • Charles McDonald
  • Eke-Eke

The Genesis Plus GX core is licensed under

A summary of the licenses behind RetroArch and its cores have found here.


Content that can be loaded by the Genesis Plus GX core have the following file extensions:

  • .mdx
  • .md
  • .smd
  • .gen
  • .bin
  • .cue
  • .iso
  • .sms
  • .gg
  • .sg
  • .68k
  • .chd


RetroArch database(s) that are associated with the Genesis Plus GX core:


Required or optional firmware files go in the frontend's system directory.


BIOS files that are labelled (bootrom) and (lock-on) must have their corresponding core option ('System bootrom' core option or 'Cartridge lock-on' core option) configured correctly in order for them to be loaded.

Filename Description md5sum
bios_MD.bin MegaDrive TMSS startup ROM (bootrom) - Optional 45e298905a08f9cfb38fd504cd6dbc84
bios_CD_E.bin MegaCD EU BIOS - Required for MegaCD EU games e66fa1dc5820d254611fdcdba0662372
bios_CD_U.bin SegaCD US BIOS - Required for SegaCD US games 854b9150240a198070150e4566ae1290
bios_CD_J.bin MegaCD JP BIOS - Required for MegaCD JP games 278a9397d192149e84e820ac621a8edd
bios_E.sms MasterSystem EU BIOS (bootrom) - Optional -
bios_U.sms MasterSystem US BIOS (bootrom) - Optional -
bios_J.sms MasterSystem JP BIOS (bootrom) - Optional - GameGear BIOS (bootrom) - Optional -
sk.bin Sonic & Knuckles ROM (lock-on) - Optional 4ea493ea4e9f6c9ebfccbdb15110367e
sk2chip.bin Sonic & Knuckles UPMEM ROM (lock-on) - Optional b4e76e416b887f4e7413ba76fa735f16
areplay.bin Action Replay ROM (lock-on) - Optional -
ggenie.bin Game Genie ROM (lock-on) - Optional -


Frontend-level settings or features that the Genesis Plus GX core respects.

Feature Supported
Core Options
RetroArch Cheats
Native Cheats
Multi-Mouse -
Disk Control
Crop Overscan


The Genesis Plus GX core's internal core name is 'Genesis Plus GX'

The Genesis Plus GX core saves/loads to/from these directories.

Frontend's Save directory

  • 'content-name'.srm (MS/GG/MD/Pico/SG-1000 Cartridge Backup save)
  • cart.brm (Sega/Mega CD RAM CART)
  • scd_E.brm (Mega CD EU Backup RAM - When the 'CD System BRAM' core option is set to per bios)
  • scd_U.brm (Sega CD US Backup RAM - When the 'CD System BRAM' core option is set to per bios)
  • scd_J.brm (Mega CD JP Backup RAM - When the 'CD System BRAM' core option is set to per bios)
  • 'content-name'.brm (Sega CD/MegaCD Backup RAM - When the 'CD System BRAM' core option is set to per game)

Frontend's State directory

  • 'content-name'.state# (State)

Geometry and timingLink

  • The Genesis Plus GX core's core provided FPS is dependent on the loaded content.
  • The Genesis Plus GX core's core provided sample rate is 44100 Hz.
  • The Genesis Plus GX core's core provided aspect ratio is dependent on the 'Core-provided aspect ratio' core option.

Loading Sega CD gamesLink

When loading Sega CD games, Genesis Plus GX needs a cue-sheet that points to an image file. A cue sheet, or cue file, is a metadata file which describes how the tracks of a CD or DVD are laid out.

If you have e.g. foo.bin, you should create a text file and save it as foo.cue. If the Sega CD game is single-track, the cue file contents should look like this:

 FILE "foo.bin" BINARY
  TRACK 01 MODE1/2352
   INDEX 01 00:00:00

After that, you can load the foo.cue file in RetroArch with the Genesis Plus GX core.

Certain Sega CD games are multi-track, so their .cue files might be more complicated.

Here's a cue file example done with Lunar - Eternal Blue (USA)


For Sega-CD games, ISO + WAV, BIN + CUE and ISO + OGG formats are supported; ISO + MP3 is not supported.

Core optionsLink

The Genesis Plus GX core has the following option(s) that can be tweaked from the core options menu. The default setting is bolded.

Settings with (Restart) means that core has to be closed for the new setting to be applied on next launch.

  • System hardware [genesis_plus_gx_system_hw] (auto/sg-1000/sg-1000 II/mark-III/master system/master system II/game gear/mega drive / genesis)

    Choose which system is going to be emulated.

  • System region [genesis_plus_gx_region_detect] (auto/ntsc-u/pal/ntsc-j)

    Choose which region the system is from.

  • System lockups [genesis_plus_gx_force_dtack] (enabled/disabled)

    Emulate system lockups that occur on real hardware.

  • System bootrom [genesis_plus_gx_bios] (disabled/enabled)

    Runs bootrom if available and then starts loaded content after the boot sequence. Look above at the BIOS section for more information.

  • CD System BRAM [genesis_plus_gx_bram] (per bios/per game)

    The Sega CD's internal memory cannot hold a lot of saves. Setting this core option to per game allows each game to have its own one brm file, thus negating any lack of available space issues.

  • 68k address error [genesis_plus_gx_addr_error] (enabled/disabled)

    Emulate the 68k address error that occurs on real hardware. Set this to disabled when playing rom hacks since most emulators used to develop rom hacks don't emulate the error.

  • Cartridge lock-on [genesis_plus_gx_lock_on] (disabled/game genie/action replay (pro)/sonic & knuckles)

    Select lock-on cartridge. Look above at the BIOS section for more information.

  • Master System FM (YM2413) [genesis_plus_gx_ym2413] (auto/disabled/enabled)

    Enable the Master System FM chip. (Enhanced sound output support for SMS compatible games.

  • Mega Drive / Genesis FM [genesis_plus_gx_ym2612] (mame (ym2612)/mame (asic ym3438)/mame (enhanced ym3438)/nuked (ym2612)/nuked (asic ym3438)/nuked (discrete ym3438))

    Awaiting description.

  • Sound output [genesis_plus_gx_sound_output] (stereo/mono)


  • Audio filter [genesis_plus_gx_audio_filter] (disabled/low-pass)

    Awaiting description.

  • Low-pass filter % [genesis_plus_gx_lowpass_range] (5 to 95 in increments of 5. *60 is default)

    Awaiting description.

  • Blargg NTSC filter [genesis_plus_gx_blargg_ntsc_filter] (Off/monochrome/composite/svidio/rgb)


Blargg NTSC filter - Off

Blargg NTSC filter - monochrome

Blargg NTSC filter - composite

Blargg NTSC filter - svideo

Blargg NTSC filter - rgb

  • LCD Ghosting filter [genesis_plus_gx_lcd_filter] (disabled/enabled)
LCD Ghosting filter - On

  • Borders [genesis_plus_gx_overscan] (disabled/top/bottom/left/right/full)


  • Game Gear extended screen [genesis_plus_gx_gg_extra] (disabled/enabled)


Game Gear extended screen - Off

Game Gear extended screen - On

  • Core-provided aspect ratio [genesis_plus_gx_aspect_ratio] (auto/NTSC PAR/PAL PAR)

    Choose the Core-provided aspect ratio. RetroArch's aspect ratio must be set to Core provided in the Video settings for this to function properly.

  • Interlaced mode 2 output [genesis_plus_gx_render] (single field/double field)

    Change how interlaced mode 2 output is handled. Games like Sonic 2's multiplayer mode uses Interlaced Mode 2.

Interlaced mode 2 output - single field

Interlaced mode 2 output - double field

  • Show Lightgun crosshair [genesis_plus_gx_gun_cursor] (disabled/enabled)

    Shows lightgun crosshairs for the 'MD Menancer', 'MD Justifiers', and 'MS Light Phaser' Device Types.

Lightgun crosshair

  • Invert Mouse Y-axis [genesis_plus_gx_invert_mouse] (disabled/enabled)

    Inverts the Mouse Y-axis for the 'MD Mouse' Device Type.

  • CPU speed [genesis_plus_gx_overclock] (100%/125%/150%/175%/200%)

    Overclock the emulated CPU.

  • Remove per-line sprite limit [genesis_plus_gx_no_sprite_limit] (disabled/enabled)



The Genesis Plus GX core supports the following device type(s) in the controls menu, bolded device types are the default for the specified user(s):

User 1 device typesLink

User 2 device typesLink

Other controllersLink

  • PICO tablet - The Genesis Plus GX core can emulate PICO tablet inputs but this is done automatically, based off the game's crc, and cannot be manually selected as a device type.
  • Terebi Oekaki tablet - The Genesis Plus GX core can emulate Terebi Oekaki table inputs but this is done automatically, based off the game's crc, and cannot be manually selected a device type.

Multitap supportLink

Activating multitap support in compatible games can be configured by the 4-WayPlay, Teamplayer, Master Tap device types for the corresponding users.

Controller tablesLink


User 1- 8 Remap descriptors RetroPad Inputs MD Joypad 3 Button MD Joypad 6 Button MS Joypad 2 Button MS Paddle Control MS Sports Pad MD XE-1AP
B B B 1 1 1 E2
A A A E1
Mode Mode Select
Start Start Start Start Start Start Start
D-Pad Up D-Pad Up D-Pad Up D-Pad Up
D-Pad Down D-Pad Down D-Pad Down D-Pad Down
D-Pad Left D-Pad Left D-Pad Left D-Pad Left
D-Pad Right D-Pad Right D-Pad Right D-Pad Right
C C C 2 2
X Paddle Trackball X Thumb-stick X
Y Trackball Y Thumb-stick Y
X Slider Y
Y Slider X


RetroMouse Inputs MD Mouse
Mouse Cursor MD Mouse Cursor
Mouse 1 MD Mouse Left
Mouse 2 MD Mouse Right
Mouse 3 MD Mouse Start
Wheel Down MD Mouse Center


RetroPointer Inputs MS Graphic Board
or Pointer Position MS Graphic Board Stylus
Mouse 1 MS Graphic Board Pen
Mouse 2 MS Graphic Board Menu
Mouse 3 MS Graphic Do


RetroLightgun Inputs MD Menacer MD Justifier MS Light Phaser
or Pointer Position MD Menacer Crosshair MD Justifier Crosshair MS Light Phaser Crosshair
Gun Trigger MD Menacer A MD Justifier A MS Light Phaser A
Gun Aux B MD Menacer B MD Justifier B MS Light Phaser B
Gun Start MD Menacer Start MD Justifier Start MS Light Phaser Start
Gun Start MD Menacer C MD Justifier C MS Light Phaser C


Inputs PICO tablet Terebi Oekaki tablet
or Pointer Position PICO tablet Stylus Terebi Oeka tablet Stylus
Mouse 1 PICO tablet Pen Terebi Oeka tablet Pen
Mouse 2 PICO tablet Red
Mouse 3 Terebo Peka tablet Start
Wheel Up PICO tablet Previous page
Wheel Down PICO tablet Next page
PICO tablet Up (White)
PICO tablet Down (Orange)
PICO tablet Left (Purple)
PICO tablet Right (Green)


100% compatibility with Genesis / Mega Drive, Sega/Mega CD, Master System, Game Gear & SG-1000 released software (including all unlicensed or pirate known dumps), also emulating backwards compatibility modes when available. It also has Pico emulation.

See alsoLink

Sega - Master System - Mark IIILink

Sega - Mega Drive - GenesisLink

Sega - Mega-CD - Sega CDLink

Sega - PICOLink

Sega - SG-1000Link