FSB Design Guidelines
R
80
Intel
®
855PM Chipset Platform Design Guide
To connect to the debug port, follow the steps below:
Route the TDI signal between the ITP700FLEX connector and the processor. A 150-
± 5% pull-
up to V
CCP
(1.05 V) should be placed within ± 300 ps of the TDI pin.
Route the TMS signal between ITP700FLEX connector and the processor. A 39.2-
± 1% pull-up
to V
CCP
should be placed within ± 200 ps of the ITP700FLEX connector pin.
Route the TRST# signal between ITP700FLEX connector and the processor. A 510-
to 680-
±
5% pull-down to ground should be placed on TRST#. Placement of the pull down resistor is not
critical. Avoid having any trace stub from the TRST# signal line to the termination resistor.
Route the TCK signal from the ITP700FLEX connector’s TCK pin to the processor’s TCK pin and
then fork back from the processor’s TCK pin and route back to ITP700FLEX connector’s FBO pin.
A 27.4-
± 1% pull-down to ground should be placed within ± 200 ps of the ITP700FLEX
connector pin.
Route the TDO signal from the processor to a 54.9-
± 1% pull-up resistor to V
CCP
that should be
placed close to ITP700FLEX connector’s TDO pin. Then insert a 22.6-
± 1% series resistor to
connect the 54.9-
pull-up and “TDOITP” net (see Figure 41). Limit the L1 segment length of the
TDOITP net to be less than 1.0 inch.
The processor drives the BPM[4:0]# signals to the ITP700FLEX at a 100-MHz clock rate. Route the
BPM[4:0]# as a Zo=55
point-to-point transmission line connection between the processor and the
ITP700FLEX connector. Connect the ITP700FLEX connector’s BPM[3:0]# pins to processor’s
BPM[3:0]# pins. Connect the ITP700FLEX’s BPM[4]# signal to processor’s PRDY# pin. The
ITP700FLEX’s integrated far-end terminations as well as the processor’s AGTL+ integrated on-die
termination guarantee proper signal quality for the BPM[4:0]# signals. Due to the length of the
ITP700FLEX cable, the length L2 of the BPM[4:0]# signals on the motherboard should be limited to be
shorter than 6.0 inches. The BPM[4:0]# signals’ length L2 should be length matched to each other
within ± 50 ps. The BPM[4:0]# signal trace lengths are matched inside the processor package, thus
motherboard routing does
not
need to compensate for any processor package trace length mismatch.
Due to the processor’s AGTL+ on-die termination for BPM[3:0]# and PRDY#, there is no issue or
concern if the BPM[4:0]# pins of the ITP700FLEX connector are left floating when the ITP is not
being used and the ITP700FLEX cable is unplugged.
Route the ITP700FLEX connector’s BPM[5]# signal as a Zo = 55
point-to-point connection to
the processor’s PREQ# pin. Integrated on the ITP700FLEX BPM[5]# driver signal is a resistive
pull-up that guarantees proper signal quality at the processor’s PREQ# input pin. The processor has
an integrated, weak, on-die pull-up to V
CCP
for the PREQ# signal to guarantee a proper logic level
when the ITP700FLEX port connector is not plugged in. There is no need for any external
termination on the motherboard for the BPM[5]# = PREQ# signal. The maximum length of
BPM[5]#/PREQ# should not exceed 6.0 inches.
As explained in Sections 4.1.5 and 4.1.5.1, the RESET# signal forks (see Figure 26) out from the Intel
855PM MCH’s CPURST# pin and is routed to the processor and ITP700FLEX debug port. One branch
from the fork connects to the processor’s RESET# pin and the second branch connects to a 54.9
± 1%
termination pull-up resistor to V
CCP
placed close to the ITP700FLEX debug port. A series 22.6
± 1%
resistor is used to continue the path to the ITP700FLEX RESET# pin with the RESETITP# net in Figure
41. The length of the RESETITP# net (labeled as net L4) should be limited to be less than 0.5 inches
There is no need for pull-up termination on the processor side of the RESET# net due to presence of
AGTL+ on-die termination on the processor and the MCH.
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