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It is impossible to open the motorized tray with a cartridge inserted, as the BIOS which controls it will not run then.

At all other times (without a cartridge inserted), pressing reset will return to the Mega-CD title screen, but will not open the tray. In the original Mega-CD model which has the motorized front-loading tray, pressing reset while the title screen is displayed will open the tray (eject the disc) or close it (load the disc). Except when a game disc is in the drive, if no button is pressed at the Mega-CD title screen, the animation and music will loop indefinitely. If no disc is inserted, it prompts on screen for one while playing the title animation and music. On all second revisions of the Mega-CD boot ROM, if the user has a Mega Mouse or Sega Mouse plugged into control port 2, this may be utilized as a pointing device instead of using a traditional control pad. It will also run this software on a game disc if A, B, or C is pressed before the game auto-starts.įrom the CD player, it is also possible to enter a utility to manage items in the game backup RAM and RAM carts, or to start an inserted Mega-CD game disc (without resetting the console). If a regular audio CD or a CD+G disc is inserted, it waits for button A, B, or C on the first controller to be pressed, then starts the GUI CD/CD+G player software in ROM. If a game disc is inserted, it automatically loads the game after a few seconds, or immediately if Start is pressed on the controller. Both CPU run together a program which checks the disc while displaying a Mega-CD (or Sega CD) title animation with music utilizing the sound hardware of both the Mega Drive and the Mega-CD. Then the Mega-CD CPU runs other code of the BIOS.

If the cartridge slot is empty at power-up, a part of the BIOS is mapped to the Mega Drive CPU memory map and is run by the Mega Drive CPU, which decompresses other part of the BIOS onto the Mega-CD memory. If a cartridge is inserted, the Mega Drive ROM starts it, and the Mega-CD remains idle, except for the audio mixer, which passes through the Mega Drive audio to its RCA outputs. When the Mega Drive + Mega-CD is powered on, the Mega Drive CPU gets control first.