Intel CHIPSET 820E - Manual (Page 75)

Intel ® 820E Chipset
R
Design Guide 75
2.9.1. 8-Bit Hub Interface Routing Guidelines
This section documents the routing guidelines for the 8-bit hub interface. This hub interface connects the
ICH2 to the MCH. This interface supports two buffer modes: normal and enhanced. The ICH2 uses its
HLCOMP pin to set the buffer mode, and the MCH uses its HLA_ENH# pin to configure its 8-bit hub
interface buffers. Both devices must be configured for the same buffer mode.
When the buffers are configured for normal mode, the trace impedance must equal 60 Ω ± 10%. In the
enhanced buffer mode, the trace impedance can be 50 Ω ± 10% or 60 Ω ± 15%.
Table 15. 8-Bit Hub Interface Buffer Configuration Setting
Component Hub Interface Buffer Mode Trace Impedance Strap
Normal/Single 60 Ω HLCOMP pulled to V
CC
1_8 (see Note) ICH2
Normal/Local 50 or 60 Ω HLCOMP pulled to GND (see Note)
Normal/Single 60 Ω Default MCH
Normal/Local 50 or 60 Ω HLA_ENH# pulled to GND via a 100 Ω resistor
Note: Refer to Section 2.9.1.4 for the specific resistor value
2.9.1.1. 8-Bit Hub Interface Data Signals
The 8-bit hub interface data signal traces should be routed 5 mils wide with 20 mils trace spacing (5 on
20). These signals can be routed 5 on 15 for navigation around components or mounting holes. To break
out of the MCH and ICH2 package, the hub interface data signals can be routed 5 on 5. The signal must
be separated to 5 on 20 within 300 mils of the package.
The maximum hub interface data signal trace lengths in the normal and enhanced buffer modes are 8
inches and 14 inches, respectively. Each data signal must be matched within ±0.1 inch of the HL_STB
differential pair. There is no explicit matching requirement between the individual data signals.
2.9.1.2. 8-Bit Hub Interface Strobe Signals
The hub interface strobe signals should be routed 5 mils wide with 20 mils trace spacing (5 on 20). This
strobe pair should have a minimum of 20 mils spacing from any adjacent signals. The maximum length
for the strobe signals in normal mode is 8 inches and in enhanced mode is 14 inches. Each strobe signal
must be the same length, and each data signal must be matched within ±0.1 inch of the strobe signals.
2.9.1.3. 8-Bit Hub Interface HUBREF Generation/Distribution
HUBREF is the hub interface reference voltage. Depending on the buffer mode (i.e., normal or enhanced
buffer mode), the HUBREF voltage requirement must be set appropriately for proper operation. See
Table 16 for the HUBREF voltage specifications for normal and enhanced buffer modes and the
associated resistor recommendations for the voltage divider circuit.