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AGP Port Design Guidelines
R
Intel
®
855PM Chipset Platform Design Guide
173
Table 41. AGP 2.0 Routing Guideline Summary
Signal
Maximum
Length
Trace
Spacing
(4 mil
traces)
Length Mismatch
Relative To
Notes
1X Timing Domain
10 in
4 mils
No Requirement
N/A
None
2X/4X Timing
Domain Set#1
6 in
8 mils
± 0.1 in
AD_STB0 and
AD_STB0#
AD_STB0, AD_STB0#
must be the same
length
2X/4X Timing
Domain Set#2
6 in
8 mils
± 0.1 in
AD_STB1 and
AD_STB1#
AD_STB1, AD_STB1#
must be the same
length
2X/4X Timing
Domain Set#3
6 in
8 mils
± 0.1 in
SB_STB and
SB_STB#
SB_STB, SB_STB#
must be the same
length
Miscellaneous
10 in
8 mils
No Requirement
N/A
PCI_PME#,
AGP_PERR#,
AGP_SERR#
Each strobe pair must be separated from other signals by at least 15 mils.
7.3.3.
AGP Clock Skew
The maximum total AGP clock skew, between the Intel 855PM MCH and the graphics component, is 1
ns for all data transfer modes. This 1 ns includes skew and jitter, which originates on the motherboard,
add-in module (if used), and clock synthesizer. Clock skew must be evaluated not only at a single
threshold voltage, but also at all points on the clock edge that falls in the switching range. The 1 ns skew
budget is divided such that the motherboard is allotted 0.9 ns of clock skew (the motherboard designer
shall determine how the 0.9 ns is allocated between the board and the synthesizer).
7.3.4.
AGP Signal Noise Decoupling Guidelines
The main focus of these guidelines is to minimize signal integrity problems on the AGP interface of the
Intel 855PM MCH. The following guidelines are not intended to replace thorough system validation on
Intel 855PM chipset-based products.
A minimum of six 0.01-µF capacitors are required and must be as close as possible to the MCH.
These should be placed within 70 mils of the outer row of balls on the MCH for VDDQ
decoupling. Ideally, this should be as close as possible.
The designer should evenly distribute placement of decoupling capacitors in the AGP interface
signal field.
Intel recommends that the designer use a low-ESL ceramic capacitor, such as with a 0603 body-
type X7R dielectric.
In order to add the decoupling capacitors within 70 mils of the MCH and/or close to the vias, the
trace spacing may be reduced as the traces go around each capacitor. The narrowing of space
between traces should be minimal and for as short a distance as possible (1.0 inch max.).
Содержание 855PM
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Страница 22: ...Introduction R 22 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 32: ...General Design Considerations R 32 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 124: ...Platform Power Requirements R 124 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 182: ...Hub Interface R 182 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 228: ...I O Subsystem R 228 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...
Страница 328: ...Platform Design Checklist R 328 Intel 855PM Chipset Platform Design Guide This page intentionally left blank...