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Sega CD

Overview

The Sega CD application (also known as Mega-CD) is an emulator for the Sega CD (CD-ROM accessory) for the Sega Genesis.

Adding Games (Feed Editor)

Due to large Disc image sizes, adding Sega CD-based games in the Feed Editor must be done manually (versus using auto-detection).

Important

The Sega CD application only supports .CHD and .PBP disc file formats (.ISO, .BIN, and .CUE are not supported).

See the Disc-based Items section for the list of steps required to add a Sega CD game in the Feed Editor.

Important

Both the iOS Safari and Xbox Series X|S Edge browsers limit the amount of memory that can be consumed by a particular web application (such as webЯcade).

The current limit is around 450 megabytes. Therefore, loading larger disc sizes may fail.

To increase the likelihood of a game with a larger disc size loading, you can optionally choose to launch the game using a standalone-based link (versus launching the game within the webЯcade player or editor). See the Standalone section of this documentation for further information (On Xbox, you would most likely want to bookmark the direct link. On iOS, you would most likely want to add the game to the home screen).

BIOS Files

In addition to Sega CD Disc images, a set of Sega CD BIOS files must be specified globally within the feed (See the Feed Properties Dialog and Sega CD Feed Properties sections).

A single BIOS file for each region (USA, Japan, and Europe) must be specified (for a total of 3 BIOS files):

File Hash (MD5) Region Description
bios_CD_J.bin 278a9397d192149e84e820ac621a8edd Japan Model 1 v1.00p (1991)
bios_CD_U.bin 2efd74e3232ff260e371b99f84024f7f USA Model 1 v1.10 (1992)
bios_CD_U.bin 854b9150240a198070150e4566ae1290 USA Model 2 v2.00w (1993)
bios_CD_U.bin ecc837c31d77b774c6e27e38f828aa9a USA Model 2 v2.11x (1993)
bios_CD_U.bin baca1df271d7c11fe50087c0358f4eb5 USA CDX v2.21x (1993)
bios_CD_E.bin e66fa1dc5820d254611fdcdba0662372 Europe Model 1 v1.00 (1992)
bios_CD_E.bin 9b562ebf2d095bf1dabadbc1881f519a Europe Model 2 v2.00 (1993)
bios_CD_E.bin b10c0a97abc57b758497d3fae6ab35a4 Europe Model 2 v2.00w (1993)

Settings

The Sega CD Application includes a custom settings dialog.

To access these settings, display the "Pause" screen and select the "Sega CD Settings" option (See screenshot above).

Display Tab

The Sega CD Application "display tab" settings are detailed below.

Field Description
Force bilinear filter

Forces bilinear interpolation on the output display. Enabling bilinear filtering produces display output where pixels are not as sharp and pronounced.

Enabling this setting will override the global bilinear filter setting for the Sega CD application.

Controls

The emulator supports up to two controllers. The keyboard and gamepad mappings are listed in the tables below.

Keyboard

Keyboard support is only available for controller one.

Name
Keys
Comments
Move
A
B
C
X
Y
Z
Start
Mode The Right Shift Key.
Show Pause Screen

Gamepad

Gamepad support is available for both controllers.

Name
Gamepad
Comments
Move  or 
A
B
C
X
Y
Z
Start Not available for Xbox and not recommended for iOS (see alternate)

Press the Menu (Start) Button.
Start
(Alternate)
 and  Hold down the Right Trigger and click (press down) on the Right Thumbstick.
Mode Not available for Xbox and not recommended for iOS (see alternate)

Press the View (Back) Button.
Mode
(Alternate)
 and  Hold down the Right Trigger and click (press down) on the Left Thumbstick.
Show Pause Screen  and  Not available for Xbox and not recommended for iOS (see alternate 3 or 4)

Hold down the Left Trigger and press the Menu (Start) Button.
Show Pause Screen
(Alternate)
 and  Not available for Xbox and not recommended for iOS (see alternate 3 or 4)

Hold down the Left Trigger and press the View (Back) Button.
Show Pause Screen
(Alternate 2)
 and  Not available for Xbox and not recommended for iOS (see alternate 3 or 4)

Hold down the X Button and press the View (Back) Button.
Show Pause Screen
(Alternate 3)
 and  Hold down the Left Trigger and click (press down) on the Left Thumbstick.
Show Pause Screen
(Alternate 4)
 and  Hold down the Left Trigger and click (press down) on the Right Thumbstick.

RAM Cart and Backup RAM Storage

The Sega CD application supports preserving state from the Sega CD RAM Cart and Backup RAM between sessions. This state is persisted in the browser's local storage or optionally to cloud-based storage. State information will be persisted whenever the pause screen is displayed (or the game is exited). Therefore, the pause screen should be displayed periodically to ensure the state is properly persisted.

Feed

This section details how Sega CD application instances can be added to feeds.

Type

The type name for the Sega CD application is retro-genplusgx-segacd.

Note

The alias segacd also currently maps to this application. In the future, the segacd alias may be mapped to another Sega CD application (different emulator implementation) if it is determined to be a more appropriate default.

Feed Properties

The table below contains global Sega CD feed properties. These properties must be specified in the props object of the feed's Feed Object.

Property Type Required Details
segacd_bios Array of URLs Yes

An array of URLs to Sega CD BIOS files.

See the BIOS Files section for additional information.

Item Properties

The table below contains the properties that are specific to the Sega CD application. These properties are specified in the props object of a feed item.

Property Type Required Details
uid String Yes

A unique identifier for the particular game (must be unique across all Sega CD games).

This identifier is primarily used to associate persistent state with the game.

discs Array of URLs Yes

Array of URLs to one or more (for multi-disc games) Sega CD game discs.

The Sega CD application only supports .CHD and .PBP disc file formats (.ISO, .BIN, and .CUE are not supported).

zoomLevel Numeric No A numeric value indicating how much the display image should be zoomed in (0-40).

This property is typically used to hide the black borders that are present on some Sega CD games.

Example

The following is an example of a complete feed that consists of a single Sega CD application instance (type value of segacd). The discs property value contains a URL that points to a Sega CD game disc image. The uid property value contains a unique identifier for this specific game (must be unique across all Sega CD games).

It is also worth noting that the Sega CD BIOS locations (segacd_bios) is specified globally within the Feed Object's props object.

{
  "title": "Sega CD",
  "props": {
    "segacd_bios": [
        "https://<host>/bios_CD_E.BIN",
        "https://<host>/bios_CD_J.BIN",
        "https://<host>/bios_CD_U.BIN"
    ]
  },
  "categories": [
    {
      "title": "Sega CD Games",
      "items": [
        {
          "title": "Some Game",
          "type": "segacd",
          "props": {
            "uid": "6c93b5db-47fe-40a8-902d-036353a28d70",
            "discs": [
                "https://<host>/somegame.chd"
            ]
          }
        }
      ]
    }
  ]
}

References

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