Re: Clearing CMOS Vs. Loading Bios Deafults
- From: nospam@xxxxxxxxxx (Paul)
- Date: Sun, 20 Aug 2006 23:43:15 GMT
In article <Y9qdnSegJprP4nrZnZ2dnUVZ_q-dnZ2d@xxxxxxxxxxxx>, "Ken Maltby"
"Paul" <nospam@xxxxxxxxxx> wrote in message
In article <rqbFg.7955$rI5.7115@xxxxxxxxxxxxxxxxxxxxxxxxxx>, "Jeff"
Question,,,,,,With 5 hard drives and all working semi-ok now ( 4 out of
restarts are fast, one takes forever)
Will clearing the cmos perhaps clear out perhaps some junk in the bios
(though i flashed the bios today)
i mean what advantages does clearing out a cmos have over loadingt bios
Thanks to the experts here from whom i continue to learn from
Clearing the CMOS with the hardware jumper, clears all 256 bytes
of RAM inside the Southbridge.
"Load Setup Defaults" will at least re-write those bytes that
are used by the BIOS code. I cannot say for certain whether it
clears all bytes first or not.
Some DOS BIOS flashing programs have a number of options to be
used during the flash operation. One command line option is
to clear the CMOS, and presumably that clears the whole thing.
Clearing the CMOS with the jumper, should also reset the RTC
(real time clock). The RTC is in the Southbridge next to the RAM.
When you enter the BIOS setup screen, the clock should be
reset to some goofy value. That is handy, in fact, to check
whether the CMOS clearing procedure worked or not. I believe
I've had cases here, where after I thought I cleared the CMOS,
the clock in the BIOS still had the correct time. So I use that
as one test to see whether the CLRTC jumper has done its job
or not. When using the CLRTC jumper, always remember to unplug
the computer before using the jumper (that is usually stated
in the instructions in the manual, and is to prevent damage).
It may still be true (or not) that you should unplug the MB from
the power supply, so that the charge still in the capacitors won't
effect the process. It used to be that the portion of the circuit on
the MB itself would take much less time to discharge its capacitors
than it would take for those in the power supply. So it was either
remove the power connector from the power supply or leave the
jumper on for a lot longer. It's easy enough to pull the Molex
power connector so I still just do that, after pulling the power to
the power supply.
No, it is an actual damage issue. The problem is, on some boards,
the battery and a power source derived from +5VSB are diode ORed
together. The battery path has a 1K ohm (current limiting) resistor
in the path, and the reason that works, is the power consumption of
the Southbridge while on battery is very low (microamps). When the
Southbridge is working, the CMOS power consumption is a lot higher,
and sufficient power must be present for read/write operations
to the CMOS well. They don't stick a current limiting resistor
in the +5VSB derived power path. If a user uses the clear CMOS
jumper, with the +5VSB present, it can actually physically burn
one of the two diodes inside the three-legged dual diode (K45
type). I have helped at least one person to repair their board
after damaging it that way - they managed to solder two ordinary
diodes in place of the burned three-legged device.
Therefore, since the design method for each clear CMOS implementation
is unknown, but because there is a known design defect in a large
number of motherboard types, it pays to unplug the computer so
that there is no chance of +5VSB being present when the jumper
Some Southbridge chips are clever enough, to have a digital signal
on the interface for clearing the CMOS. In that case, the designers
don't need to interfere with the power path, and they can use the
reset signal instead. But I believe in some cases, you will still
find the brain-dead power path method in use, even when a
signal for that purpose is present on the chip.
Better to just unplug it.
- Prev by Date: Re: Flashed SP97-V BIOS - Now won't boot
- Next by Date: K8N - Sempron 2600+ L&C psu
- Previous by thread: Re: Clearing CMOS Vs. Loading Bios Deafults
- Next by thread: Re: Clearing CMOS Vs. Loading Bios Deafults