Hello again everyone I have another question whats the best but safest speed i.e. not game breaking clock to OC the 68000 to? or is it better to just change out the cpu for like a 68010? although some games then wont work due to the default higher clock any thoughts or ideas? 10Mhz 12Mhz ??? My Genesis im intending to do this mod to has the Motorola MC68000P8 cpu and its a v6.5 motherboard model P.S. also seperate Q whats a good set of small heatsinks for the dual 7805's just wanting ones that are smaller for it
10Mhz seems to work good with Sonic 1 from what I've heard so that might be a better choice. I was actually going to attempt this myself on my Model 1 VA6 but nobody seems to have the install information for a Hitachi CPU, which I heard are the best for overclocking. A couple games and the 32X can overclock the Genesis to about 13MHz and a more simple mod can let you overclock it to that speed for as long as you have the switch set to overclock mode. Virtua Racing (Genesis Version) is a game off the top of my head that overclocks the system.
10MHz is the most stable but if you plan to use the Sega CD you need to use the standard clock, I've overclocked my model 2 and 10MHz is the most stable and works rather well.
The clock signal for the CPU can't be "overclocked" by a cartridge device. The crystal/oscillator that clocks the CPU is hard wired and there is no provision for any cartridge to modify it. Virtua Racing contains the "SVP" chip which Sega was experimenting to see what they could do in a similar way to Nintendo's Super FX and other chips. I also have heard that the 10mhz overclock is more compatible than some other frequencies. Mainly I have heard the lazy method of overclocking to something like a 13mhz signal available on the cartridge port tends to offer poor results. As for the heatsinks I'm not sure. I don't think you'd want to go with smaller heat sinks than the original design unless you are planning on added active cooling like a small fan.
I remember reading somewhere that the Genesis can be overclocked to about 13MHz via pins on the cart slot. It seems the link to the page is dead so I can't find more information on it.
Yes, there is a 13mhz signal on the Cartridge slot. But you can't make a cartridge that overclocks the Genesis's 68000 CPU. What people do is they will cut the 68000's clock signal line and wire a switch with one position connecting the original clock and the other connects the 13mhz signal on the cartridge port. Again there is no way to alter the clock speed of the Genesis without internal modification. Also, this 13mhz overclock has poor compatibility. I recall reading it will work for a game like Sonic 2 if you switch to the high speed mode after the game starts or something like that. The somewhat harder thing to do is to install a second crystal that is 10mhz to have the original stock speed and 10mhz selectable.
Here is the link to an easy to follow tutorial. http://www.sega-16.com/forum/showth...ck-your-sega-genesis-model-1-and-NOTHING-ELSE
I've seen that guide before. It's quite helpful. I have a question that nobody I've talked to seems to want to answer or just doesn't know the answer. Is the overclock mod the same for all of the different CPU brands in the Genesis Model 1? My Genesis VA6 has a Hitachi CPU in it and I was wondering if that CPU needs different things for the mod. I've also heard that the Hitachi CPUs are rare in North American Genesis units but the best for overclocking.
It doesn't matter what 68000 is in your Genesis if you're willing to replace the 68000 with one that is rated for the higher clock speed. So if you're comfortable desoldering the whole CPU that is always an option. Or have someone else do that for you.
i read that 2 of the 3 cpu's ran games much faster one the hiachi and 2 the sig but moto was slow and needs a oc for some games but stands stable with 10mhz like mentioned n thx for the replies P.S. im fully ok with desoldering the CPU for another better designed CPU at same clock if what i just mentioned holds ground being 2 of the 3 cpu's are faster initially with no OC needed I also have a Hakko FR-300 and it desolders pins well with no damage so far
All Genesis consoles have a 68000 CPU running at the same speed (7.5mhz approx). Any difference ever mentioned is that some are stable at higher clock speeds and some are not. It would not make sense if certain models of the system did not have the CPU running at the same speed. It could break compatibility if the timing was seriously off. To improve performance in games that experience slow down you will have to OC the system and hope that is enough. If you find or know that the CPU you have doesn't like being overclocked to 10mhz, you'll need to replace it with one that can handle it.
I'm with everyone else, 10mhz is what I found to be a very sweet spot on stock CPUs for the model 1, model 2, and JVC X'EYE.
what will DTACK waitstates do for the cpu? never heard of this but i'd like to know knowledge is power
It will cause the CPU to wait a longer while before it acknowledges that it received the data from the source (DaTa ACKnowledgement), allowing slow memories like EPROM to work. The idea is make it so different memory ranges have different DTACK/System clock wait state ratios. For example I could keep the VDP without any extra waitstates, put two extra waitstates (additionally on top of what the bus arbiter already insert) for cartridge ROM and zero waitstates for the system RAM (which I replaced with 32KB 10ns i80486 cache SRAM chips).
The lazy cartridge pin over-clocking method is "unstable" due to a simple factor: Many cartridges suffer with the increased bus speed (cartridge components like the ROM chip itself not able to handle it). But the overall system stability is rock solid. If you have a decent flash cartridge or even one of the old "floppy to cart" devices like the famous "magic drive" you can play any game over-clocked without freezing the console, the reason for this being the better components of such cartridges that can handle the increased clock rate. The improvement for games like f22 or split-screen Sonic 2 are massive.
