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Intel
®
820E Chipset
R
128 Design Guide
Table 32. GPIO
Checklist Items Recommendations Reason/Effect
GPIO pins GPIO[0:7]:
• These pins are in the main power well. Pull-ups must
use the 3.3 V plane.
• Unused core well inputs must either be pulled up to
VCC3.3 or be pulled down. These inputs must not be
allowed to float.
• GPIO[1:0] can be used as REQ[A:B]#.
• GPIO[1] also can be used as PCI REQ[5]#.
• These signals are 5 V tolerant.
Ensure that all unconnected
signals are outputs only!
GPIO[8] & [11:13]:
• These pins are in the resume power well. Pull-ups
must use the VCCSUS3.3 plane.
• Unused resume well inputs must be pulled up to
VCCSUS3.3.
• These are the only GPIs that can be used as ACPI-
compliant wake events.
• These signals are not 5 V tolerant.
These are the only GPI
signals in the resume well
with associated status bits in
the GPE1_STS register.
GPIO[16:23]:
• Fixed as output only. Can be left NC.
•
In the main power well
•
GPIO22 is open-drain.
GPIO[24, 25, 27, 28]:
• I/O pins. Can be left NC.
• From resume power well
Table 33. USB Interface
Checklist Items Recommendations Reason/Effect
USBP[3:0]P
USBP[3:0]N
See Figure 56 for the circuitry needed on
each differential pair.