Product specifications

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Preliminary Revision 0.5, November 19, 1999 42 Motherboard Design Guidelines
Technologies, Inc.
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2.4.1.2 Socket-370 Host Interface to North Bridge
The recommended topology for the Socket-370 host signals to North Bridge (VT82C694X) is shown in Figure 2-34. For signal
quality considerations, the trace length of the host signals should be minimized. 56 ohm pull-ups to VTT near the Socket-370
CPU are required.
• It is recommended to route all host signals to VT82C694X in equal length and as short as possible. A minimum of 5 mils
in width and a minimum of 10 mils in spacing are required for those host signals. Wide traces for VTT pull-ups are
recommended.
• There is no stub before traces L1 and L2. Two traces directly come out the pin of the Socket-370. The location of these
56 ohm resistor networks should be as close to Socket-370 CPU as possible.
• The most qualified range of the L1 trace length is between 1.5 inches and 4.5 inches. The trace length of L2 should be
less than 2 inches.
VTT
VT82C694X
(North Bridge)
Socket-370
CPU
1.5 < L1 < 4.5"
L1
ADS# ADS#
DEFER#
DBSY#
BR0#
RESET#
LOCK#
HIT#
DRDY#
BNR#
BPRI#
REQ[4..0]#
TRDY#
HITM#
RS[2..0]#
BNR#
BPRI#
DEFER#
DBSY#
BREQ0#
CPURST#
HLOCK#
HIT#
DRDY#
HREQ[4..0]#
HTRDY#
HITM#
RS[2..0]#
L2 < 2"
A[31..3]
A[31..3]
D[63..0]D[63..0]
56 ohm
Figure 2-34. Socket-370 Host Interface Topology Example
A layout example for the host interface between the Socket-370 CPU and the VT82C694X chip is shown in Figure 2-35. The
VTT rail (a minimum of 200 mils wide) covering three sides of the Socket-370 on the component layer can provide a sufficient
GTL+ termination voltage supply path in Figure 2-35 (a).