Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
Stephan Grossklass wrote:
> P2B schrieb:
>
>>Stephan Grossklass wrote:
>>
>>>A number of USB2 cards will not run when the PCI bus does not provide
>>>3.3V (as it's the case for the P2B-D(S)
>>
>>Interesting. In that case why does the 3.3v LED on my POST diagnostic
>>card light up when it's plugged into a P2B-DS PCI slot?
>
>
> Well, it could be that Asus added PCI 2.2 support later, like Gigabyte
> apparently did on the GA-6BXD. (Incidentally, what's the big difference
> between 2.1 and 2.2 anyway? I always thought it's mostly 3.3V standby
> power.) You do not happen to have one of those stubborn USB2 cards that
> refuse to work in, say, an older P2B?
That's possible, but I don't think it's the answer - I've worked on a
lot of P2Bs and never seen the 3.3v LED off unless there was a VIO
problem, including (recently) a P2B-DS 1.04 and a P2B 1.02.
I don't know much about PCI specifications, and to date I've gotten by
with the onboard USB ports - so no USB2 cards here, stubborn or
otherwise
🙂
>>Just the other day I fixed a P2B-DS with no power to the memory - the
>>3.3v LED was off initially, but came on as usual after I replaced a FET
>>in the 3.3v regulator circuitry.
>
>
> Hmm. This would imply that the +3.3V supplied to the PCI bus comes from
> the VIO voltage regulator. That should be okay with the default 3.20 V
> I/O, but 3.5 V (as to be found on all the other Asus BX boards) would
> already be out of the +/- 5% tolerance.
Bit hard to tell, but it appears to be VIO at the PCI slot. I just poked
around on the P2B-DS 1.06 I have running on the bench (with modified
VIO), and measured 3.48v at the ATX power connector, and 3.38v at both
the DIMM and PCI slots. BIOS shows 3.4v.
I suppose to really understand you'd have to download PCI specs and
probe the board more extensively. It might explain why Asus set VIO
lower on the dual P2Bs, which has always been something of a mystery to me.
P2B