JoyMega
This page was last modified 14:52, 25 April 2020 by Mars2000you. Based on work by Sd snatcher and Grauw and others.

Contents

Description

JoyMega is a DIY adapter that allows connecting Sega Genesis/Mega Drive game controllers to MSX. By default, buttons B and C are mapped to the triggers 1 and 2 of the MSX, respectively. The adapter fully support up to 8 buttons (A, B, C, Start, X, Y, Z, Mode).

Some modern games provide native support for the additional buttons, others are patched to use them, instead of keyboard keys for example. If you use the loader SofaRom by Louthrax you can set a keyboard key on each button.

The adapter has an open design which is easy to make yourself if you know a bit of soldering. Adapters are also sold online by various people.

The first design of JoyMega used a 74LS04 Hex Inverter IC, which was later changed to a 74HCT04 to reduce current draw and improve compatibility with picky MegaDrive controllers which have 74HC* chips inside.

A variation using a transistor instead of an inverter IC was made as well, which reduces the current draw as well but is said to have more compatibility issues, resulting in button ghosting and glitches on many MSX models/controllers. This unofficial variation is not recommended.

A new revision called JoyMega2 is sold here. It does not add new functions, but it is made with a single gate inverter (NC7ST04) instead of the 74HCT04 (hex inverter) that contains six gates. A capacitor has also been added to avoid possible parasites. These changes reduce the size and current draw, and improve the reliability and compatibility.

The latest revision is called JoyMega3. Besides the NC7ST04 chip, it also adds diodes for the pins 6 and 9 of the Megadrive controller, to protect against bus contention if the pins 6 and 7 of the MSX joystick connector are configured for output (i.e., if PAD(0) is used on MSX-BASIC).

Characteristics:

  • No driver or modification need
  • Fully MSX compatible, and the extra buttons are available for use in your program
  • Compatible with the MSX-HID plug-and-play detection
  • Single mode of operation. No need to switch between "legacy" and "advanced" modes
  • Very cheap and easy to build. No translation micro-controllers are required (zero lag). Uses only classic components.
  • Also supports other devices like the Sega Multitap (MK-1654 and compatibles)
  • Low power consumption (Joystick port limit is 50 mA):
    • JoyMega (74LS04 chip): between 6.6 mA and 18 mA, depending on the chip maker
    • JoyMega (74HCT04 chip): 20μA
    • JoyMega2 (NC7ST04 chip): 2μA
    • JoyMega3 (NC7ST04 chip): 2μA

Limitations

  • Does not support Sega Master System devices, they require specific adapters.
  • Does not support the Sega Menacer light gun

Gallery

DIY JoyMega adapter
JoyMega adapter by MSXCalamar
DIY JoyMega adapter
JoyMega adapter by KMTech
JoyMega adapter by RoadFighter
JoyMega adapter Rev.2 by FRS & FBLabs

Patches that allows to play with the extra buttons

Games/Software that support extra buttons

Links