joyMega

JoyMega3: Mega Drive to MSX Controller Adapter

The JoyMega3 is a hardware adapter designed to interface SEGA Mega Drive (Genesis) 3-button and 6-button controllers with the MSX joystick port.

Based on the JoyMega project by Sergio Guerrero Miralles and refined by FRS, this Revision 3 version offers several hardware improvements:

Logic Chip: Uses the NC7ST04M5X inverter, providing a more compact footprint and lower power consumption compared to the original 74HCT04 design.
Signal Protection: Features two 1N5711 (or BAT85) Schottky diodes. These protect the MSX hardware against bus contention if pins 6 and 7 are accidentally configured as outputs (e.g., when using PAD(0) in MSX-BASIC).
Multiplexing: The adapter inverts the TH signal (Pin 8 on MSX) to ensure that the D-pad and primary buttons are active by default.

Standard Mode: Out of the box, the 'B' button acts as Trigger 1 and the 'C' button acts as Trigger 2, maintaining compatibility with standard MSX software.
Extended Mode: Compatible software can access all buttons (A, B, C, Start, X, Y, Z, and Mode) by toggling Pin 8.
Compatibility: Works with 3-button and 6-button Mega Drive controllers on any MSX, MSX2, MSX2+, or TurboR system.

Form Factor: Compact internal PCB design.
Power: Draws +5V directly from the MSX joystick port.
Testing: Fully compatible with diagnostic tools such as JoyTest and HID Tester.

Disclaimer: This is a hobbyist hardware project. Use at your own risk.