Dreamcast Serial Port Overclock?

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Morphv2
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Dreamcast Serial Port Overclock?

Post by Morphv2 » Mon Aug 06, 2007 1:07 am

Ok, I was searching for information about the Dreamcast's serial port, when I came across this website.

http://f17.aaa.livedoor.jp/~takotako/

In there he had a lot of neat schematics and stuff, stuff in which I've posted it's content before. However, something different caught my eye this time.

http://f17.aaa.livedoor.jp/~takotako/dc ... scitst.gif

I am not exactly sure what he was doing (although it appears he was messing with DC <-> DC connection), it mentions a 24MHz clock signal for the serial port. Well, 24/16(I'm assuming the the bus width) = 1.5mbps. That is the maximum speed of the serial port.

Then it hit me. When you overclock a Dreamcast, you are overclocking the Front Side Bus. Therefore, EVERYTHING is getting overclocked. A Dreamcast running at 240MHz should theoretically increase the speed of everything on the system by about 20%. Therefore (unless the serial port gets it's clock feed from a seperate independant source), the serial port should be running 20% faster. 1.5 + 20% = 1.8. Your serial port should now have a maximum throughput of 1.8mbps.

So hows about this for an idea. Since many people complain the serial port is too slow, why not just overclock the port itself? Find the 24MHz clock signal, and sub in, say, 48MHz? Your serial bus and the serial bus alone would then be running at 3mbps, which is PLENTY of headroom for homebrew connectors of pretty much any sort. Perhaps a Serial NIC would be possible, hm?
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henzenmann
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Re: Dreamcast Serial Port Overclock?

Post by henzenmann » Mon Aug 06, 2007 2:54 am

The SH4's serial port can be supplied with an external clock (24MHz oscillator on the DC to USB converter). Since it is difficult to find a baud rate that is matched by both the default SH4 ones and the USB serial port chips, this feature is used to force the SH4's serial port to a baud rate that is compatible with the USB chip. In theory the SH4's serial port can go up to 3mpbs, but it will probably not work over an external cable.
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