Design Guide

Hub Interface
R
192 Intel
®
855GM/855GME Chipset Platform Design Guide
Figure 89. ICH4-M and GMCH Locally Generated Reference Voltage Divider Circuit
ICH4
HIREF
R3
R2
C4
VCCHI
C2
HI_VSWING
R1
C1
C3
GMCH
HLVREF
R3
R2
C6
VCCHI
C5
PSWING
R1
C1
C3
10.3.3. Single GMCH and ICH4-M Voltage Generation / Separate
Divider Circuit for VSWING/VREF
This section describes the option to use one voltage divider circuit for VREF, shared by both ICH4-M
and GMCH, while using another voltage divider circuit for VSWING. This allows for tuning the two
reference voltages independently. The reference voltage for both HIVREF and HI_VSWING must meet
the voltage specification in Table 81. Normal care needs to be taken to minimize crosstalk to other
signals (< 10-15 mV).
Figure 90. Shared GMCH & ICH4-M Reference Voltage with Separate Voltage Divider Circuit for
VSWING and VREF
HIREF
V
CC
HI=1.5V
Intel
®
ICH4
R4
R5
C1
HI_VSWING
C3
R6
R7
HLVREF
PVSWING
C5 C2
C4
C6
GMCH
R4 = 43.2 Ω ± 1%,
R5 = 49.9 Ω ± 1%,
R6 = 78.7 Ω ± 1%,
R7 = 24.2 Ω ± 1%
C1 and C3 = 0.1 µF
(near divider)
C2, C4, C5, C6 =
0.01µF (near
component)
Table 83. Recommended Resistor Values for Separate HIVREF and HI_VSWING Divider Circuits
Signal Recommended Resistor Values VCCHI Capacitor value
HIVREF
(350mV)
R4 = 43.2 Ω ± 1%
R5 = 49.9
Ω ± 1%,
VCCHI=1.5 V C3 = 0.1 µF (near divider)
C2, C5 = 0.01 µF (near component)
HI_VSWING
(800mV)
R6 = 78.7 Ω ± 1%
R7 = 24.2
Ω ± 1%,
VCCHI=1.5 V C1 = 0.1 µF (near divider)
C4, C6 = 0.01 µF (near component)