by Vladimir Vega 👾
◆ Overclocking has always interested me, ever since the old MS-DOS days, but I always had the impression that the retro gaming scene was rarely interested in it. For the most part, you’d mainly see various RGB video, region, and audio mods circulating the internet. However, Sega Genesis was a notable exception. Its overclocking scene started back in the early 2000s with nerds like Deven Gallo. While his OC solution didn’t catch on with the general public back then, it gained widespread popularity years later when the retro scene exploded.
As many of us know <or might not know>, the Sega Mega Drive is powered by the iconic Motorola 68000 CPU, a legendary processor also found in the Commodore Amiga, Atari ST, early Macintosh computers, Neo-Geo MVS, Sharp X68000, and countless arcade JAMMA boards. Running at a clock speed of 7.67 MHz, it’s remarkably similar to the chip inside the Amiga <7.09 MHz>. Thanks to this shared architecture, many 16-bit titles back in the day were easily ported from the Amiga to the Mega Drive/Genesis and vice versa.
On top of that, the Genesis packed an additional 8-bit Zilog Z80 coprocessor, making its dual-CPU setup structurally similar to NeoGeo MVS hardware even though the NeoGeo ran its 68000 at a much faster 12MHz and had vastly superior graphics hardware. Still, this shared M68k/Z80 framework made the Genesis a natural home for several SNK arcade ports, including Samurai Shodown, Fatal Fury, Art Of Fighting, World Heroes, Viewpoint, and King Of The Monsters. However, developers loved pushing the Genesis hardware to its absolute limits. As a result, even standout titles like Sonic The Hedgehog 2, Gunstar Heroes, Thunder Force IV, and Viewpoint frequently suffered from noticeable “slowdowns” when things got chaotic on screen, especially when too many sprites overlapped or during heavy explosions. It could be pretty jarring for players, and the framerate drops were even more painfully obvious in pseudo-3D and early 3D games.
The ultimate solution to these performance dips is an Overclock Mod. Beyond simply eliminating frame drops, it breathes new life into the games. In certain titles, it delivers a butter-smooth experience that feels remarkably like playing on a NeoGeo arcade cabinet, which shouldn’t come as a surprise, given that this upgrade brings the Genesis’s CPU clock speed right up to MVS levels! While some enthusiasts recommend sticking to a more conservative 10MHz mod for overall system stability, running the system at 12MHz has proven to be equally reliable in practice. The beauty of this mod lies in its switchable design, allowing you to easily toggle the console back to its stock 7.67 MHz speed at any moment. While a few games might not play nice with overclocking due to their tight timing loops and optimization, the vast majority will run like a charm.
Okay, let’s go through this step by step. As with most hardware projects, what you’ll need is a good soldering iron, some colored wires, a 3-pin 2-position toggle switch, and a 12 MHz 4-pin quartz COC oscillator <DIP14>. All of these components are inexpensive and easy to find at almost any well-stocked electronics store.
For the base, you can use a small piece of perfboard to make the oscillator completely stable. Also, if you wish, you can add two small heatsinks to your Motorola processor. In this particular case, I’m using the Mega Drive Model 1 console as an example, but the same principle and approach applies to Model 2.
STEP 1.
The first step is to locate pin-15 on the Motorola processor and disconnect it from the board, as shown in the picture. The pins are numbered from left to right.
Solder the white wire <or whatever color you have> to the pin we disconnected, and solder the other end to the center pin of the switch. Solder the yellow wire to the motherboard pad where pin-15 was attached, and connect the other end to the first pin of the switch.
With these connections, setting the switch to the first position returns the console to its original 7.67MHz clock.
STEP 2.
Take the oscillator and locate the marked corner <usually a sharp edge or a small dot>, that is pin-1. The pin opposite it is pin-2, and so on.
The pinout is as follows :
Pin-1 – NC <No Connection> ; Pin-2 – VCC <+5V Power>
Pin-3 – GND/Ground ; Pin-4 – 12mhz Clock
Locate the nearest capacitor on the board; the <+> mark indicates +5V VCC, while the <–> mark indicates GND <Ground>. Solder a wire from the positive pad of the capacitor to pin-2 on the oscillator, and a wire from the negative pad to pin-3 on the oscillator. Solder pin-4 of the oscillator to the third pin on the switch. Now, setting the switch to the second position engages the 12 MHz clock!
IMPORTANT: Always power on the console in its native mode, then switch to 12MHz with the toggle switch. The console will freeze for a moment, after that press the reset button and continue using it normally. Always keep this procedure in mind, as otherwise you could cause damage to the CPU!
One response to “TIPS & TRICKS : Sega Mega Drive 12Mhz Overclock <ARCHIVE>”
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