Overclocked dreamcast

[Alexvrb]

[quote author=quzar link=board=hardware;num=1094318646;start=0#4 date=09/04/04 at 23:58:37]

There are many different things you can do to manually overclock a CPU idependantly of the FSB. Like I said this was mostly a problem back in the p2/p3 era.
[/quote]Indeed, but increasing the CPU speed independently of the FSB in a PC wouldn't cause the problem you were thinking of. Uh, not in recent times anyway, although even further back, just raising the multiplier shouldn't cause problems even with 486s (just given as an example of a way to increase clock without touching the bus... which is why I wouldn't directly compare OCing DC to PC). Anyway, if the issue is ever resolved maybe we can get a better guide (and in English too).

[Mental2k]

wonder ho hard it would be to make a dc into an atomisewave machine...

[Kamjin]

[quote author=qatmix link=board=hardware;num=1094318646;start=0#9 date=09/05/04 at 14:06:36]Thanks,

looking at the webpage, (and some of my other DC motherboards). The actual chip number is different on the DC i modded. Its still labelled as the same component on the motherboard as my older DC (with the pipes). However this is a revision 1 mobo not a revision 0 which that is.

I however very much doubt that this is the issue. Kajaming does your DC have the pipes etc?
[/quote]

The motherboard I'm looking at is the heat pipe version, it's actually dead though.. but you're connected in the right place.

I tried disconnecting the crystal and the DC doesnt work. so that goes to show the crystal is connected and making a through signal.

That actually shows you're in the right spot.

I dont have the ceramic capacitor on it however. What differnce will that make? Ive also tried another different 40 mhz crystal(this one does not have a nc Â*on it (What is that btw?).

Wires have an inductance (a resistance to a change of current), the longer and thiner the wire then the more inductance it will have, also the higher the frequency the higher the inductance, so what happens is that the wires that feed the ground, and power to the xtal begin to act like resistors (actualy they'll start oscillating as well) The cap will act like a little reservoir for the xtal, that way you're sure the the signal it's creating isn't flawed. In reality it might be a little to low of a signal so the cpu isn't catching some of the ticks.

The NC/Case is simply a contact to the metal case of the xtal module, you'd normally connect it to the sheild ground so it won't cause radio interference.

Is there someway that I might need to ensure that the pin is not 'arc'ing with the wire on the mobo and overriding the circuit?

Doubtfull, since when you remove the xtal it stops working it proves that there's no contact.

Sorry for all the questions, im sooo close and I think this will be an interesting mod for all of the dc community, so Im trying to get it sorted.
Q

When I have some time I'm going to open up a DC and start to look at it as well, I'd say to try and get a hold of other values between 33-40Mhz and see how they change the behavior. in the end it just might be that the 40Mhz is causing the CPU some sort of internal error that's slowing it down..

Uh, not in recent times anyway, although even further back, just raising the multiplier shouldn't cause problems even with 486s (just given as an example of a way to increase clock without touching the bus

Unfortunately the multiplier is at the max, so we're kinda stuck in that sense. Although early press releases from Sega had the CPU clocked at 210 or 225Mhz so they must have been overclocking it when they were developing it.

[quzar]

[quote author=qatmix link=board=hardware;num=1094318646;start=0#9 date=09/05/04 at 14:06:36]Thanks,

looking at the webpage, (and some of my other DC motherboards). The actual chip number is different on the DC i modded. Its still labelled as the same component on the motherboard as my older DC (with the pipes). However this is a revision 1 mobo not a revision 0 which that is.[/quote]

There were two different versions of the SH chip used in the dreamcast. About a year ago i bought an eBay lot of 22 DCs and parts. From them I learned much about the different revisions. Basically other than the different place and date differences, the main difference is that older chips say something like sh4400 or something, then the newer ones say the same thing, but with an R at the end. There are also two versions of the PVR chip.

[Mekanaizer]

hi

quzar wrote:

There were two different versions of the SH chip used in the dreamcast. About a year ago i bought an eBay lot of 22 DCs and parts. From them I learned much about the different revisions. Basically other than the different place and date differences, the main difference is that older chips say something like sh4400 or something, then the newer ones say the same thing, but with an R at the end. There are also two versions of the PVR chip.

The diference in the SH4:

• The sh4xxx is the original Hitachi, sh7750

• The sh4xxxR is the Renesas revision of the sh7750 named sh7750R

They are the same but Renesas owns it now
this helps


-Mekanaizer-

[quzar]

Are you POSITIVE about that? When I asked Renesas they said that they really didnt know about that since they were specialty modifications of a chip.

I am sorry to say, but all I can say is that this was a custom chip
that was done for Sega.

Sorry,
lyle

-----Original Message-----
From: Quzar [mailto:*******@yahoo.com]
Sent: Monday, December 08, 2003 5:37 PM
To: TechSupport
Subject: Re: FW: SH-4 chip identification.


Thank you very much. If you could also maybe tell me
any information about the differences between the
BP200 HD6417091 and BP200 HD6417091R chips? or maybe
what the HD number means? I would apreciate it greatly
if you could. Thank you.

~****** ******

[Alexvrb]

They're saying that the SH4 used in all DCs is a custom version of the SH4. Has extra instructions over the standard SH7750. All DCs have those instructions, and I'd say its safe to say they're essentially identical.

[Kamjin]

Suprised he didn't tell you.. since it's just the actual company name
HD = Hitachi Denshi
64 = should denote the sh
1 = This used to denote a FLASH or memory option on the older products
7091 = The actual model of the cpu (7750 on normal sh4's)
BP = is the Package (256pin BGA)
200 = Speed
There's an R+S suffix I'm not 100% sure on that but it either denotes a shrink of the dye, or a technology change.

[Alexvrb]

[quote author=Kamjin link=board=hardware;num=1094318646;start=0#12 date=09/05/04 at 16:18:05]Unfortunately the multiplier is at the max, so we're kinda stuck in that sense. Although early press releases from Sega had the CPU clocked at 210 or 225Mhz so they must have been overclocking it when they were developing it.[/quote]
I know, I was just giving an example relating to 486s. That's why I noted that you shouldn't directly compare PC overclocking to DC. The examples and info based on typical x86 boxes often don't apply.

[quzar]

[quote author=Kamjin link=board=hardware;num=1094318646;start=15#17 date=09/06/04 at 00:25:02]There's an R+S suffix I'm not 100% sure on that but it either denotes a shrink of the dye, or a technology change.[/quote]

I had the feeling that was the case. But I still wasn't sure. This could still be important in that it may tell us if certain DC processors give off less heat or such.