178 Design Guide
Intel
®
855GME Chipset and Intel
®
82801DB ICH4 Embedded Platform Design Guide
AGP Port Design Guidelines
7.2.4 AGP Signal Noise Decoupling Guidelines
The main focus of these guidelines is to minimize signal integrity problems on the AGP interface
of the Intel chipset GMCH. The following guidelines are not intended to replace thorough system
validation on Intel chipset-based products.
• A minimum of six 0.01-µF capacitors are required and must be as close as possible to the
GMCH. These should be placed within 70 mils of the outer row of balls on the GMCH 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.
• To add the decoupling capacitors within 70 mils of the GMCH and/or close to the vias, 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.).
In addition to the minimum decoupling capacitors, the designer should place bypass capacitors at
vias that transition the AGP signal from one reference signal plane to another. One extra 0.01 uF
capacitor per 10 vias is required. The capacitor should be placed as close as possible to the center
of the via field.
7.2.5 AGP Interface Package Lengths
Table 63. AGP Interface Package Lengths (Sheet 1 of 2)
Signal
Pin
Number
Package
Length (mils)
Signal Pin Number
Package
Length (mils)
GAD0 T6 339 GADSTB_0 P3 475
GAD1 T5 362 GADSTBB_0 P4 439
GAD2 R5 440 GADSTB_1 J3 601
GAD3 R3 489 GADSTBB_1 J2 675
GAD4 R4 415 GSBA_0 E5 686
GAD5 R6 343 GSBA_1 F5 617
GAD6 P5 387 GSBA_2 E3 738
GAD7 P6 409 GSBA_3 E2 865
GAD8 N5 466 GSBA_4 G5 668
GAD9 N3 504 GSBA_5 F4 688
GAD10 N2 568 GSBA_6 G6 518
GAD11 M5 510 GSBA_7 F6 613
GAD12 M1 611 GSBSTB F2 799
GAD13 M3 520 GSBSTBB F3 761
GAD14 M2 566 GPIPEB D5 644
GAD15 T7 296 GCBEB_0 P2 553
GAD16 L5 440 GCBEB_1 L2 583
GAD17 K6 491 GCBEB_2 L4 515
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