Design Guide

AGP Port Design Guidelines

184 Intel

855GM/855GME Chipset Platform Design Guide

9.2.6. AGP Routing Ground Reference

Intel strongly recommends that at least the following critical signals be referenced to ground from the

GMCH to an AGP controller connector using a minimum number of vias on each net: AD_STB0,

AD_STB0#, AD_STB1, AD_STB1#, SB_STB, SB_STB#, G_TRDY#, G_IRDY#, G_GNT#, and

ST[2:0].

9.2.7. Pull-ups

The AGP 2.0 Specification requires AGP control signals to have pull-up resistors to VDDQ to ensure

they contain stable values when no agent is actively driving the bus. Also, the AD_STB[1:0]# and

ST_STB# strobes require pull-down resistors to GND. The GMCH has integrated many of these pull-

up/pull-down resistors on the AGP interface and a few other signals not required by the AGP 2.0

Specification. Pull-ups are allowed on any signal except AD_STB[1:0]# and SB_STB#.

The GMCH has no support for the PERR# and SERR# pins for AGP graphics controller with PERR#

and SERR# support. Pull-ups to a 1.5-V source are required down on the motherboard in such cases.