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Old 02-19-2005, 06:45 PM
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[Excalibur] [Excalibur] is offline
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Exclamation I925X/XE tuning on P5AD2 series

Hi all,
it seems that some issues observed in the previous pages of this thread regard the critical tuning of the North Bridge I925X (4x200MHz) or I925XE (4x266MHz).
It's known that North Bridge chip is responsible of the connection between most important heart-part of your system: CPU (via FSB), RAM (via RAMbus), PCI-express bus, South Bridge (for peripherals).

Well, it's true that all of you have talked about CPU and RAM settings, but NOBODY about PCI-express frequency.
There's a little trick from ASUS: in these mobos, "PCI express frequency" set to AUTO sucks. Why?
Designed for overclocking applications, the default setting AUTO seems to be NOT the regular value FSB / 2 (at defaults PCI-e frequency should be generated from the same PLL that drives the FSB quad-pumped, the so-called TO CPU synchro in BIOS: so, if PLL freq is 200MHz, we obtain 800 MHz for FSB and 100MHz for PCI-express), but seems to be, instead, slightly LESS.
Of course, some PCI-e video cards suffers about under-clocked buses (ATI Radeon in particular. Note that it's not an ATI issue, it's an ASUS trick!), and can generate black screen, BSOD (blue screen of death), restart of the system 'cause instability between data on PCI-e and North Bridge.

So, if you have strange instability issues on P5AD2 and P5AD2-E, try to disregard AUTO setting on PCI-express frequency. Set it to a manual value between 102-105 MHz for non-overclocked systems, and PEG Link Mode to SLOW (i.e. simply not try to boost communications between PCI-e bus and North Bridge, but only use freq. specified).

It's also true that if you overclock the system, you MUST increase manually this PCI-express frequency, too. Or North Bridge will suffer of some kind of arbitration loss of data. Values between 105 and 110 MHz for overclocked systems should run well.

Greetings from Italy

Last edited by [Excalibur]; 02-19-2005 at 07:25 PM.
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