Intel 6300ESB ICH, Design Manual

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January 2007 233
Intel
®
855GME Chipset and Intel
®
6300ESB ICH Embedded Platform Design Guide
Intel
®
6300ESB Design Guidelines
For more information on General Purpose Event (GPE) Register recommendations for Microsoft
Windows
*
operating systems refer to the document GPE Routing for Microsoft Windows, which
can be found at http://www.microsoft.com/whdc/hwdev/tech/onnow/GPE_routing.mspx
9.11 RTC
The 6300ESB contains a real time clock (RTC) with 256 bytes of battery backed SRAM. The
internal RTC module provides two key functions: keeping date and time and storing system data in
its RAM when the system is powered down.
The 6300ESB uses a crystal circuit to generate a low-swing 32 KHz input sine wave. This input is
amplified and driven back to the crystal circuit through the RTCX2 signal. Internal to the
6300ESB, the RTCX1 signal is amplified to drive internal logic as well as generate a free running
full swing clock output for system use. This output ball of the 6300ESB is called SUSCLK. This is
illustrated in
Figure 127 .
For further information on the RTC, consult Application Note AP-728 ICH Family Real Time
Clock (RTC) Accuracy and Considerations Under Test Conditions
. This application note is valid
for the 6300ESB.
Even when the 6300ESB internal RTC is not used, it is still necessary to supply a clock input to
RTCX1 of the platform because other signals are gated off that clock in suspend modes. However,
in this case, the frequency accuracy (32.768 KHz) of the clock inputs is not critical; a crystal may
be used or a single clock input may be driven into RTCX1with RTCX2 left as no connect, as shown
in
Figure 128 .
Note: This is not a validated feature on 6300ESB. Please note that the peak-to-peak swing on RTCX1
may not exceed 2.0 V.
Figure 127. RTCX1 and SUSCLK Relationship in 6300ESB
B1180-02
Internal
Oscillator
Low-Swing 32.768 kHz
Sine Wave Source
Full-Swing 32.768 kHz
Output Signal
Intel
®
6300ESB
I/O Controller
Hub
RTCX1
SUSCLK