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
system settings.
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 .
