Re: Adventures in replacing motherboard battery.

In article <9_-dnQS9abNEXp3eRVn-jQ@xxxxxxxxxxx>, "James Silverton"
<not.jim.siverton.at.comcast.not> wrote:

> Hello, All!
>
> After the advice posted in the last day or two, I summoned up
> the courage to replace the battery on my A7V333 motherboard! By
> the way, it is a CR2032 and cost $3.20 at Radio Shack and is
> common to all Asus desktop mother boards according to the net.
> Apart from getting at the old battery to remove it in the rather
> confined space where I keep my machine, things went well. I did
> switch off the power and wait until the green light went out!
> AFAIK, the non-default BIOS settings were retained.
>
> There were some problems when I switched on and rebooted in that
> I could not persuade my cordless mouse to work. Finally,
> pressing the computer reset button did the job! The only small
> puzzle was the momentary appearance of a message saying "ECSD
> successfully updated"-------any information?
>
> I still have to see if the clock keeps going properly in an
> overnight shut off.
>
> Thanks again to everyone for the information posted.
>
> James Silverton
> Potomac, Maryland, USA

>From one of those dictionary sites on the web:

"ESCD or Extended System Configuration Data is a part of CMOS
memory where information about Plug-and-Play devices is stored.
It's used by BIOS to allocate resources for devices like extension
cards.

BIOS also updates it each time the hardware configuration changes
with purpose to decide how to allocate resources like IRQ and memory
mapping ranges. After ESCD is updated, the decision is not needed
to be carried out again, which results in faster startup without
conflicts even when the hardware wasn't changed.

The Microsoft Windows operating system accesseses this information,
too, when working with the Device Manager."

The actual CMOS RAM on most motherboards is 256 bytes and is located
in the Southbridge. That is the RAM that is powered by the battery.
The real time clock (RTC) is also located in the same logic block
in the Southbridge, and they run off the sustaining voltage, which
is the "diode OR" of 3VSB (made from 5VSB on the power supply) and
the 3V coin cell battery.

The CMOS RAM is not big enough to hold ESCD or DMI information.
Instead, there are segments in the BIOS flash chip, that are
reserved for holding "non-volative" information. When you see the
"Updating..." message, the BIOS is actually flashing part of the
BIOS chip. Occasionally we see mention of the term "NVRAM", and
this could be another term for something stored in the BIOS flash
chip.

Any time the ESCD or the DMI does not match the current hardware
config, or the flash segment is not properly flashable any more
(so cannot be made to match the current config), you may see
the Updating ESCD message. Sometimes it can even be caused by
hardware which the BIOS cannot parse or recognize.

In the older BIOS, I believe there was also a one-time flag you
could set, to force the ESCD to be recalculated. Recent BIOS
don't seem to offer that option any more.

As for the accuracy of time keeping via the motherboard RTC,
the RTC has a 32768 Hz crystal, located next to the Southbridge.
That is the same crystal as is used in digital watches. Now, digital
watches have a small variable capacitor, which can be used to set
the oscillator frequency to exactly 32768 Hz. Motherboards don't
have one of those, so whatever offset is present, is a permanent
feature of the motherboard.

Paul
.

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