RTC section in Laptop Motherboard(Most Important)
RTC:
It keeps track
on storing the time, date and user’s system settings , Even when there
is no external
power on the board (means the G3 machincal off state) unless the on
board 3.3v
coin cell not removed.
Working and
esensital signals of RTC.
1. VCCRTC . VccRTC powers PCH RTC well which is mostly connected to the
LDO output
3.3v of 3/5v regulator .which is genraterd before pressing the power
button . and a
3.3v internal battery is used for VCCRTC too. (such as coin cell).
2. RESET# and
SRTCRST#. These signals are used to clear the
system
settings or in
simple words we can say, to clear cmos settings . these signals are
active when
low and can b asserted by removing the RTC coin battery or by shorting
the cmos clear
jumperth. These signals are also feaded from the same sourceof
VCCRTC but
through resister dividers to make these signals high and to store
3. RTCX1 and
RTCX2. Basicaly ICH/PCH uses a internal timer IC
having 256
byte of RAM
which keeps track on date, time and system settings. Ich/pch uses a
cristal
circuit to genrate a low swing sine wave of 32.768Khz at RTCX1 pin as
input to the
internal oscillator, and this input signal is amplified and driven back to the
cristal
circuit through RTCX2 pin of ICH/PCH with the same frequancy of 32.768 Khz
but with
littel higher amplitude due to amplification . thats why when we check the
cristal pins
with multimeater we found little diffrence in voltage at both pins. And it is
the first
check point whther the oscillator circuit of ICH/PCH is initallised or not .
4. Sus_clock. The RTCX1 input is amplified for the purpose to drive
internal
logic of
ICH/PCH
And genrates a
free running full swing square wave of same frequancy of 32.768
Khz as
Clock out put
for system use . this out put of ICH/PCH is known as SUS_CLOCK.
SUS_CLOCK is
the shure short way to check wether the RTC section is working
properly or
not by checking the wave form.
Thats why we
requires the DSO/CRO to check signals at motherboard as RTCX1,
RTCX2 and
SUS_CLOCK have the same frequancy of 32.768 Khz if we check with
frequany
meater but the diffrence is the wave form (shape of the wave).
5. INTRUDER#. This signals is used through a switch to find out the
cover of the
system is open
or closed . we have seen in some branded systems , COVER OPEN
SYSTEM HALT
message, which is genrated by this low signal . this signal is also a
part of the
RTC well. This signal is also kept high through VCCRTC.
6. INTVRMEN. ICH/PCH have some internal voltage regulators and to
enable
these internal
lenear regulaters an enable signal is also provided by this RTCVCC
as INTVRMEN (
internal regulater enable)
These all
signals are the part of RTC WELL and must be present to turn on the
board. In the
absence of any of these may cause not powering up the board .
Rtc cristal x1
pin .
Pure sine wave
of 32khz.
Out put of rtc
section to the cristal pin x2 .
Same frequency
of 32 khz but diffrence is amplitude . Little high amplitude due to
amplification
.
Sus_clk output
of rtc section . After pressing pwr btn . Full swing squre wave of same
32khz .
No comments