Intel VC820 Design Guide - Page 61
AGP 2.0 Routing Summary, All AGP Interfaces
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Layout/Routing Guidelines 2.7.4 This pair should be separated from the rest of the AGP signals (and all other signals) by at least 20 mils (1:4). The strobe pair must be length matched to less than ±0.1" (i.e., a strobe and its compliment must be the same length within 0.1"). All AGP Interfaces The 2X/4X Timing Domain Signals can be routed with 5 mil spacing when breaking out of the MCH. The routing must widen to the documented requirements within 0.3" of the MCH package. When matching trace length for the AGP 4X interface, all traces should be matched from the ball of the MCH to the pin on the AGP connector. It is not necessary to compensate for the length of the AGP signals on the MCH package. Reduce line length mismatch to insure added margin. In order to reduce trace to trace coupling (cross talk), separate the traces as much as possible. All signals in a signal group should be routed on the same layer. The trace length and trace spacing requirements must not be violated by any signal. Trace length mismatch for all signals within a signal group should be as close to zero as possible to provide timing margin. AGP 2.0 Routing Summary Table 2-8. AGP 2.0 Routing Summary1,2 Signal Maximum Trace Spacing Length Length (5 mil traces) Mismatch 1X Timing Domain 7.5" 5 mils No Requirement 2X/4X Timing Domain Set#1 7.25" 20 mils ±0.125" 2X/4X Timing Domain Set#2 7.25" 20 mils ±0.125" 2X/4X Timing Domain Set#3 7.25" 20 mils ±0.125" 2X/4X Timing Domain Set#1 6" 15 mils1 ±0.5" 2X/4X Timing Domain Set#2 6" 15 mils1 ±0.5" 2X/4X Timing Domain Set#3 6" 15 mils1 ±0.5" Relative To Notes N/A None AD_STB0 and AD_STB0# AD_STB1 and AD_STB1# SB_STB and SB_STB# AD_STB0 and AD_STB0# AD_STB1 and AD_STB1# SB_STB and SB_STB# AD_STB0, AD_STB0# must be the same length AD_STB1, AD_STB1# must be the same length SB_STB, SB_STB# must be the same length AD_STB0, AD_STB0# must be the same length AD_STB1, AD_STB1# must be the same length SB_STB, SB_STB# must be the same length NOTES: 1. Each strobe pair must be separated from other signals by at least 20 mils 2. These guidelines apply to board stackups with 10% impedance tolerance Intel®820 Chipset Design Guide 2-35