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Intel
®
440GX AGPset Design Guide
4-3
Debug Recommendations
The extra loading of the LAI562 requires stronger pull-up values on the target system. However,
due to the current limitations of some signal drivers, this stronger value may not be feasible.
Calculation of the correct pull-up resistor value for each of the CMOS signals should include a load
analysis based on the pull-up voltage, pull-up voltage tolerance, pull-up resistor tolerance, V
IH
and
V
IL
specifications, driver current rating, input current leakage, input timings, etc. The resulting
values may conflict.
As a result of the extra loading the following compromise pull-ups to Vcc
2.5
are recommended.
The actual value required by your system may vary depending on the logic connected and the drive
strength of the signal to the Slot 1 connector.
Inputs to the Slot 1 connector from the ITP562 Port:
•
PREQ# 150 - 330 ohm
•
TDI 150 - 330 ohm
•
TMS, TCK 1 Kohm
•
TRST# 470 - 680 ohm
(
A pull-down is recommended but a pull-up ma
y
be used
)
Inputs to the Slot 1 connector from the PIIX4E:
•
STPCLK# 430 ohm
•
SMI# 430 ohm
•
SLP# 150 - 330 ohm
Outputs from the Slot 1 connector:
•
TDO 150 ohm
•
THERMTRIP# 150 - 220 ohm
•
FERR# 150 - 220 ohm
Figure 4-1. LAI Probe Input Circuit