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R
10.7.4.
FWH V
The V
pin on the FWH is used for programming the flash cells. The FWH supports V
PP
V. If
is 12 V, the flash cells will program about 50% faster than at 3.3 V. However, the FWH only
PP
supports 12 V V
would be useful in a programmer environment, which is typically an event that occurs very infrequently
(much less than 80 hours). The V
In some instances, it is desirable to program the FWH during assembly with the device soldered down
on the board. In order to decrease programming time it becomes necessary to apply 12 V to the V
The following circuit will allow testers to put 12 V on the V
from the 3.3-V plane to which the rest of the power pins are connected. This circuit also allows the
board to operate with 3.3 V on this pin during normal operation.
Figure 89. FWH VPP Isolation Circuitry
10.8.
RTC
The ICH4-M 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 ICH4-M 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 via the RTCX2 signal. Internal to the ICH4-M, 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 ICH4-M is called SUSCLK. This is illustrated in Figure
90.
Figure 90. RTCX1 and SUSCLK Relationship in ICH4-M
Low-Swing 32.768 kHz
Full-Swing 32.768 kHz
®
Intel
852GM Chipset Platform Design Guide
Design Guidelines
PP
for 80 hours (3.3 V on Vpp does not affect the life of the device). The 12 V V
PP
PP
3.3V
Sine Wave Source
Output Signal
pin MUST be tied to 3.3 V on the motherboard.
PP
12V (From Motherboard)
1K
FET
I/O Subsystem
PP
pin while keeping this voltage separated
VPP
RTCX1
Internal
Oscillator
SUSCLK
of 3.3 V or 12
PP
pin.
PP
ICH4-M
175
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