Specifications
Intel
®
810E2 Chipset Platform
R
52 Design Guide
3.6.2. Strobe Signals
Due to their differential nature, the hub interface strobe signals should be 5 mils wide and routed 20 mils
apart. This strobe pair should be a minimum of 20 mils from any adjacent signals. The maximum length
for the strobe signals is 7”, and the two strobes should be the same length. Additionally, the trace length
for each data signal should be matched to the trace length of the strobes, within ±0.1”.
3.6.3. HREF Generation/Distribution
HREF, the hub interface reference voltage, is 0.5 * 1.8 V = 0.9 V ± 2%. It can be generated using a
single HREF divider or locally generated dividers (as shown in the following two figures). The resistors
should be equal in value and rated at 1% tolerance, to maintain 2% tolerance on 0.9 V. The values of
these resistors must be chosen to ensure that the reference voltage tolerance is maintained over the entire
input leakage specification. The recommended range for the resistor value is from a minimum of 100 Ω
to a maximum of 1 kΩ (300 Ω shown in example).
The single HREF divider should not be located more than 4” away from either GMCH or ICH2. If the
single HREF divider is located more than 4" away, then the locally generated hub interface reference
dividers should be used instead.
The reference voltage generated by a single HREF divider should be bypassed to ground at each
component with a 0.01-µF capacitor located close to the component HREF pin. If the reference voltage is
generated locally, the bypass capacitor must be close to the component HREF pin.
3.6.4. Compensation
Independent Hub interface compensation resistors are used by the 810E2 chipset’s GMCH and the ICH2
to adjust buffer characteristics to specific board characteristics. Refer to the Intel
®
810E2 Chipset
Family: 82810 Graphics and Memory Controller Hub (GMCH) Datasheet and the Intel
®
82801BA I/O
Controller Hub 2 (ICH2) Datasheet for details on compensation. The resistive Compensation (RCOMP)
guidelines are as follows:
• RCOMP: Tie the HLCOMP pin of each component to a 40-Ω, 1% or 2% pull-up resistor (to 1.8 V)
via a 10-mil-wide, 0.5” trace (targeted at a nominal trace impedance of 40 Ω). The GMCH and
ICH2 each requires its own RCOMP resistor.