Sega Genesis - Technical Specifications - Master System Compatibility

Master System Compatibility

One of the key design features of the console is its backwards compatibility with Sega's previous console, the Sega Master System. The 16-bit design is based upon the 8-bit design, albeit enhanced and extended in many areas. In order to achieve backwards compatibility, the Master System's central processor and sound chip (the Zilog Z80 and SN76489 respectively) are included as coprocessors in the Mega Drive, and the Mega Drive's Video Display Processor (VDP) is capable of the Master System's VDP mode 4, though it cannot run in modes 0, 1, 2, or 3 (so the Mega Drive is not compatible with SG-1000 software or Master System software which uses these modes).

As the cartridge slot is of a different shape, Sega released the Power Base Converter, a separate device that sits between a Master System cartridge and the Mega Drive's cartridge slot. The Power Base Converter does not contain any Master System components, instead functioning as a pass-through device, and consisting almost entirely of passive circuitry. The converter contains a top slot for cartridge-based games along with a front slot for card-based games, as well as the 3-D glasses adapter. When a Master System game is inserted, the system puts the Z80 in control, leaving the Mega Drive's main 68000 processor idle. The Power Base Converter had inferior capacitors however, meaning that after a few years use, the system may suffer from glitchy play; to rectify this the user must remove the capacitors from the board or replace them.

In Japan the device is known as the "Mega Adapter" (メガアダプタ). The Sega Mega Adapter is built for the Japanese Mega Drive cartridge slot, so it does not fit into the European Mega Drive and Genesis cartridge slot, like Japanese Mega Drive cartridges. It also has the Master System cartridge slot changed to the Sega Mark III/Japanese Master System pinout. Because of the Genesis VDP limitations listed before, it does not run SG-1000/SC-3000 games or Master System games that use the SG-1000 video modes. The Mega Adapter does not have the Yamaha YM2413 FM chip that enhances the sound of certain games. The PAL variant is called the "Master System Converter" in Europe.

The Power Base Converter is not fully compatible with the redesigned Mega Drive 2. A second version, the "Master System Converter II", was released to address this problem. This second version adapter was produced in a far smaller quantity, lacks the slot for card-based games, and was only released in Europe. The "Master System Converter II" could be used on both the original Mega Drive and the Mega Drive 2, however due to a difference in the height of the cartridge slot in the original Mega Drive a spacer at the bottom of the Master System Converter II must be removed before the device could be inserted into the original Mega Drive.

The only Master System game which does not work with this device is F-16 Fighting Falcon. It was originally thought that the game card had more pins than the adapter could interface with, but it is actually the compatibility mode of the Mega Drive/Genesis that is responsible for the game not working, not the Power Base Converter itself. This is because, as previously said, the Genesis can only run in VDP mode 4 and the game ran in a different VDP mode.

Some Master System games (such as Shanghai and Alien Syndrome) are incompatible with the Sega Genesis control pad. However, it is possible to correct this by modifying the control pad, or by using a Master System control pad instead. As it has the same connection port, the Master System pad can be plugged directly into Mega Drive controller ports without any kind of adapter.

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