Overclocking Sega Saturn

[RobIvy64]

Does anybody know where the two SH-2s recieve their clock from? I have studied schematics and I *suspect* that these CPUs overall clock is a multiple of the signal it recieves....2X I believe.

I think they each recieve 14.318 MHz, but im not 100 percent positive.

I have several games that lag and I just want to overclock it! Thanks

-R

[kendrick]

I believe this is the document you need to get you started:

http://cgfm2.emuviews.com/txt/sattech.txt

You want to go near the end of the file, and you probably won't like what you read... Processor speed, video refresh, and a bunch of other functions are all tied to the same timer and use multiples of the same signal. If it is possible to overclock this beast, I suspect that you have to split the timing or generate a separate clock signal for the video output. Just a guess, I'm not an expert by any measure and would welcome any other information that refutes my assumption.

-KKC, hacking custom switches for his Atari 7800 because the stock ones are cheaper than gas station Sangria.

[phreak97]

getting a seperate clock signal for video is not that hard.. i had to do it to my megadrive cos it lost all colour if switched to 60hz, because the colour encoder didnt know what to do with the new clock signal produced when switched to 60. and no, it wasnt switching to ntsc.

[Guest_robivy64]

I should just be able to feed the two CPU's a seperate clock directly, since the PLLs do the multiplying. It seems like the CPU runs off of what it is fed directly...unlike the Dreamcast, where what you feed it the CPU will multiply by 6, and run at.

I will feed the two SH-2s a 33 MHz signal and see what happens.

thanks for the help!

-R

[atom]

What is wrong with just changing everythings clock?

[kendrick]

The single clock is also used to time the video refresh. Because the Saturn can produce so many strange resolutions (720x576, eh?) the clock is essential for determining if the composite video output is interlaced and NTSC or PAL. If you overclock without also adjusting the clock speed of the video display process (VDP) chip, then the VDP will output something strange like 38.2 frames per second, instead of the industry standard 30 frames per second for NTSC. Great if you have an auto-adjusting RGB monitor, terrible if you're trying to output straight to a normal TV.

That's an oversimplification, of course. I'm not an expert, and I'm sure somebody schooled in the topic would be able to explain it more thoroughly than that.

-KKC, who has his lost cat back after two weeks. Happy.