Just a thought Faster 68000 Cpu in MD1??

D

Dr_Frankenmiga

Hi just a quick question and wonder if its possible.

After many years of being a Amiga owner (and still am) in my day to day upgrade and repairs of these systems I came across the wonderfull CPU known as the Motorola 68000 as used in alot of 16 BIT 80`s systems (Atari,Sega,C=)

The other day while reading about overclocking I heard that someone had fitted a 68000 from a SEGA-SATURN into a Amiga 500 (Amiga = 7.16Mhz) (Saturn 14Mhz I think?)and thus it really moved i belive this to be possible as the 68K line as almost all compatible socket wise.

I myself once fitted the rare as hell 68010 into my A500+ and reveled in its extra cache abilities and the extra I think at the time 3MHZ!!!!. :)

The question is can I fit a faster CPU to a MEGA DRIVE 1?

I seem to remember the standerd 68000 CPU came as 7Mhz,10Mhz and 14Mhz.

:huh :sarcasm: :unsure:
 
well, if you take a look at the CPU in the Megadrive you can see that's it's in oldskool DIL packaging (ie rectangular with big pins sticking out from both long sides) whereas the one in the Saturn is in (I think) PQFP packaging, is square in shape and much smaller. Also, the speed of the CPU in the Megadrive is determined by the clock crystal and not the CPU itself.

Oh btw, I opened my Megadrive I up once and I noticed there was a teensy resistor soldered between the 5th pin (counting from the lower left-hand side) and the PCB... I havent seen this in some other MD's, anyone got a clue why it's there?
 
Yes I opened a MD 1 earlier and seen that resistor between the CPU and the PCB.However another of my MD1`s from 1992 does not have it???

Hmmm then i wonder if that about the Saturn and Amiga is true as the Amiga has its CPU socketed in,it is also rectangluler not square.Unless he had some kind of acc. card which are super rare and in there A500 form came with 020`s and up hence faster and better (instruction set)than a 68000 so why mess?thats more of a downgrade.

Hmm maybe a change of crystal then?

Just a thought what kind of weird side effects whould this have on the system?I am thinking the timing whould be thrown all over the place of somet or maybe just not work?
 
Hmm, interesting thought. I have a 68020 accellerator card which uses a square 68020 and fits into the 68000 slot on an A500 motherboard. You could also mount the 68000 on top in case you needed to use it for compatibility reasons. I wonder if it would be possible to use that? Probably not, as it had RAM expansion on it as well.

What benefit would you gain from doing such a thing, though? I guess you would possibly eliminate some slowdown, but slowdown is certainly beneficial in some games (i.e. shmups). Playing Sonic CD with less slowdown would be really cool, but I'm nearly certain that changing the speed of the Genesis' 68k would break Sega CD compatibility.
 
IIRC, Vic_Viper said that he successfully fitted a higher-clock - and perhaps overclocked; I recall him saying that the Hitachi-made 68Ks were particularly nice for this in terms of power dissipation - 68K into one of his Megadrives. Presumably this was done with a dedicated clock divider, as I very much doubt that the VDP can handle different clock speeds. I think he said that this did remove slowdown in a lot of shooters.
 
You can speed up the Cpu in the Md buy cutting the pin that feeds the chip with CLK pin 15 I think, and wireing an external clock to it ie from a crystal from radioshack or maplins, just be careful not to short it to the pin next to it VCC that would be bad.

just remember the games were made with the MD running at 7 and a bit Mhz it may run different at a faster speed.
 
I though that the 68000 in the saturn was a variation on the 68K core? Because wasnt there a cheaper version of the 68K used for imbeded applications?
 
I wouldnt speed my megadrive up for games unless it was dynamic, or running something other than a game.

Really there is lag in only a few games like Gunstar hero's when it gets a bit heavy on the sprite on sprite action ;o) , or on sonic 2 2player mystic cave zone. Apart from that ohh and LHX nearly forgot that.

Since there are no timers on the Megadrive (except in the PSG i think, 2 timers) speeding up the Main CPU would send the sound out of whack and the timers in the game too (depending how they were written though).
 
Originally posted by Dr_Frankenmiga@Oct 27, 2003 @ 08:01 PM

The other day while reading about overclocking I heard that someone had fitted a 68000 from a SEGA-SATURN into a Amiga 500 (Amiga = 7.16Mhz) (Saturn 14Mhz I think?)and thus it really moved i belive this to be possible as the 68K line as almost all compatible socket wise.

I myself once fitted the rare as hell 68010 into my A500+ and reveled in its extra cache abilities and the extra I think at the time 3MHZ!!!!. :)

The question is can I fit a faster CPU to a MEGA DRIVE 1?

I seem to remember the standerd 68000 CPU came as 7Mhz,10Mhz and 14Mhz.

:huh :sarcasm: :unsure:
Click to expand...

In fact the saturn uses a Motorola 11.3MHz 68EC000 processor for its sound capabilities but this processor is still part of the 68000 family im unsure what differences there are between it and the orginal 68000 processor. Though i do remember something about the 68EC000 being more optimized towards sound.

Loads of info on the 68000 family can be found here http://www.fact-index.com/m/mo/motorola_68000.html
 
The 68EC000 is a low-power version intended for embedded use. There are no user-visible changes. The EC model can also be found in Megadrives.
 
Originally posted by i3enedek@Jun 15, 2004 @ 07:50 AM

I wouldnt speed my megadrive up for games unless it was dynamic, or running something other than a game.

Really there is lag in only a few games like Gunstar hero's when it gets a bit heavy on the sprite on sprite action ;o) , or on sonic 2 2player mystic cave zone. Apart from that ohh and LHX nearly forgot that.

Since there are no timers on the Megadrive (except in the PSG i think, 2 timers) speeding up the Main CPU would send the sound out of whack and the timers in the game too (depending how they were written though).
Click to expand...

It can cause trouble, but generally not if you just OC it a little. Like to 10Mhz. You can install a switch, too, so you can still use all your games and Sega CD/32X perfectly.
 
Originally posted by i3enedek@Jun 15, 2004 @ 07:50 AM

Since there are no timers on the Megadrive (except in the PSG i think, 2 timers) speeding up the Main CPU would send the sound out of whack and the timers in the game too (depending how they were written though).
Click to expand...

The timers are in the YM-2612, not the PSG, but they are rarely used. Most timing is based around V-Ints which occur at the same rate regardless of the processor speed.
 
As for sound, I think most games only update the sound hardware during vsync as well; ISTR that most early Genesis emulators processed sound this way, which should give you a general idea of how widespread it is.
 
Is there such a thing a s a variable clock? I think being able to control the speed to a degree just by turning a pot would be very nice and the next best thing to it being dynamic.
 
Hey, I'm Deven Gallo, a.k.a. Epicenter .. I created the MegaDrive/Genesis Overclocking section on Epic Gaming (http://www.epicgaming.net/md_oc). It's possible to raise the 68000 CPU speed from the stock 7.6 MHz to 19.6 MHz .. possibly higher. I am working on push past that point. My goal is 24 MHz, basically 3x original clock (if you round up to 8). ;)

The obvious question always is "Does the game get faster when it shouldn't?" The answer, in almost ALL cases is, no. It just doesn't lag.

On a PC, the system is NOT locked to a particular framerate. It will generate as many frames in say, Quake 3, as it possibly can. So when there is lag from the CPU or GPU being overworked, you see a 'slideshow'. However, on the MegaDrive/Genesis, the Video Display Processor (VDP) is locked to display 60 or 50 frames a second no matter what (Depending on region.) So when the 68000 is overworked and is taking MORE than 1 frame to do the work the VDP needs completed to draw it, the VDP draws the old frame over and over again.

So, when the 68000 is overclocked, the VDP no longer needs to wait. If the 68000 finsihes its work before the VDP expects it, it doesn't go ahead to the next frame, it can't. So it stays at proper speed.

The only (rare) occasions are in situations where the game needs to run as fast as possible due to an extreme stress level, so the game is NOT timed on Vertical Syncrate (50/60 Hz). Instead it's going at maximum possible speed the 68000 can handle. 2 examples (the only 2 that have been found so far, AFAIK) are the Sonic 3D Cinepack intro and Sonic 2's Special Stages.

As for stability-- I've noticed over 98% stability running at 12 MHz. It seems the ideal speed, and I can only generate the absolute minimum of lag using that clock frequency. Perhaps 1 frame repeats every few minutes at the worst-- a dramatic improvement, especially in games as lag-heavy as Gunstar Heroes (esp. 2-Player), Ecco the Dolphin (the original, the sequel was much more streamlined). It puts a real dent in 3D games like Hard Drivin', F-15 Strike Eagle II, etc.

Heat is a non-issue. The CPU will never get anywhere near its maximum temperature spec, it usually is below 80F even.

Anyway. Yes, you can replace the 68000. With some advice/encouragement from me, a friend of mine decided to try it out and put a 68010 in, which is pin/instruction compatible with the 68000. There is a considerable performance boost .. but it ALSO breaks a lot of games and can't be easily 'switched off' like a clock change, unfortunately.

As for a 68000->68020 Amiga Accelerator-- I am fairly certain these rely on software since the 68000 and 68020 are NOT directly interchangable. Same for the 68030 and up.
 
-----------Stupid advice

Did you try to overclock the VDP too?

Quite risky since the vdp is already very fast (53mhz).

If you push it to 2*53mhz, maybe the framerate will be 2time faster without garbages.

-----------End stupid advice, lol

When you play at a segacd or 32x game with the overclocked system, whats appen?

For exemple, could you try sonicCD or Bcracer?

Ho, what's about the 32x?

Both sh2 may run at 30mhz without serius problem...
 
As for a 68000->68020 Amiga Accelerator-- I am fairly certain these rely on software since the 68000 and 68020 are NOT directly interchangable. Same for the 68030 and up.
Click to expand...

Of course they're not identical, but what differences do you think would cause problems with an appropriate adapter? The only obvious thing I can think of is that games that bankswitch or run code from RAM could have problems with the cache.
 
Using the upper 8 bits of addresses has caused problems for all m68k platforms when switching CPU. At least the MOVE for SR instruction exists only on the 68000 (and 68008), others change their meaning subtly (eg. MOVEM).
 
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