FSB Design Guidelines
R
Intel
®
855PM Chipset Platform Design Guide
53
4.1.4.1.2.
Topology 1B: Open Drain (OD) Signals Driven by the Processor – FERR# and
THERMTRIP#
The Topology 1B OD signals FERR# and THERMTRIP# should adhere to the following routing and
layout recommendations. Table 9 lists the recommended routing requirements for the FERR# and
THERMTRIP# signals of the processor. The routing guidelines allows the signals to be routed as either
micro-strips or strip-lines using 55
± 15% characteristic trace impedance. Series resistor R1 is a
dampening resistor for reducing overshoot/undershoot reflections on the transmission line. The pull-up
voltage for termination resistor Rtt is V
CCP
(1.05 V).
Intel recommends that the FERR# signal of the processor be routed to the FERR# signal of the Intel
82801DBM ICH4-M. THERMTRIP# can be implemented in a number of ways to meet design goals. It
can be routed to the ICH4-M or any optional system receiver. Intel recommends that the THERMTRIP#
signal of the processor be routed to the THRMTRIP# signal of the ICH4-M. The ICH4-M’s
THRMTRIP# signal is a new signal to the I/O controller hub architecture that allows the ICH4-M to
quickly put the whole system into a S5 state whenever the catastrophic thermal trip point has been
reached.
If either FERR# or THERMTRIP# is routed to an optional system receiver rather than the ICH4-M and
the interface voltage of the optional system receiver does not support a 1.05-V voltage swing, then a
voltage translation circuit must be used. If the recommended voltage translation circuit described in
Section 4.1.4.2 is used, the driver isolation resistor shown in Figure 24, Rs, should replace the series
dampening resistor R1 in Topology 1B. Thus, it is important to note that R1 will no longer be required
in such a topology.
Figure 17. Routing Illustration for Topology 1B
L2
VCCP
L3
Rtt
L1
Intel ICH4-M
(or sys. receiver)
R1
Intel
Pentium M
processor
Table 9. Layout Recommendations for Topology 1B
L1 L2 L3 R1
Rtt
Transmission Line
Type
0.5” – 12.0”
0” – 3.0”
0” – 3.0”
56
± 5%
56
± 5%
Micro-strip
0.5” – 12.0”
0” – 3.0”
0” – 3.0”
56
± 5%
56
± 5%
Strip-line
Содержание 855PM
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