Intel 820E manual Bit Hub Interface Routing Guidelines, Bit Hub Interface Data Signals

Intel® 820E Chipset

R

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
	ICH2		Normal/Single	60 Ω		HLCOMP pulled to VCC 1_8 (see Note)
			Normal/Local	50 or 60 Ω		HLCOMP pulled to GND (see Note)
	MCH		Normal/Single	60 Ω		Default
			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.

Design Guide 75