Intel® 865G/865GV Chipset Datasheet - download.intel.nl - Intel

Functional DescriptionTable 28. AGP 3.0 Downshift Mode ParametersParameterAGP 2.0 Signaling(All Data Rates)AGP 3.0 Signaling(4X Data Rate)AGP 3.0 Signaling(8X Data Rate)Data rate 1X, 4X 4X 8XVREF level 0.75 V 0.35 V 0.35 VSignaling 2.0 (1.5 V)3.0 signaling(0.8 V swing)3.0 signaling(0.8 V swing)Polarity of GREQ, GGNT,GDEVSEL, GFRAME, GIRDT, Active low Active high Active highGTRDY, GSTOP, RBF, WBFPolarity of SBA normal (111 = idle) inverted (000 = idle) inverted (000 = idle)GCBE polarity GC/BE# GC#/BE GC#/BEStrobe definitionStrobeStrobeFirstStrobeFirstStrobe#StrobeSecond StrobeSecondDBI used? No Disabled on xmit YesPIPE# allowed Yes No NoCommands supported AGP 2.0 commands AGP 3.0 commands AGP 3.0 commandsIsoch supported No (Not supported) NoCalibration cycles included No Yes Yes5.3.3.1 Mechanism for Detecting AGP 2.0, AGP 3.0, orIntel ® DVOTwo new signals are provided in the AGP 3.0 specification to allow for detection of an AGP 3.0capable graphics card by the motherboard and an AGP 3.0 capable motherboard by the graphicscard respectively.The signals are:• GC_DET#: Pulled low by an AGP 3.0 graphics card; left floating by an AGP 2.0 graphicscard.• MB_DET#: Pulled low by an AGP 3.0 motherboard; left floating by an AGP 2.0 motherboard.The 3.0 capable motherboard uses GC_DET# to determine whether to generate VREF of 0.75 V(floating GC_DET# for 2.0 graphics card), or 0.35 V (GC_DET# low) to the graphics card. This issent to the graphics card via the VREFCG pin on the AGP connector.Similarly, the 3.0 capable graphics card uses MB_DET# to determine whether to generate VREF of0.75 V (floating MB_DET# on 2.0 motherboard), or 0.35 V (MB_DET# low) to the motherboard.The card could also use this pin as a strap to determine 2.0 or 3.0 mode. Note, however, thatVREFGC is not used by the GMCH. Instead, VREFCG is used to account for the DVO ADD card,where VREFGC is not connected.The GMCH detects whether the graphics card connected is AGP 2.0 or AGP 3.0 via the voltagelevel driven into the GVREF pin (0.35 V{< 0.55 V} = AGP 3.0; 0.75 V{>0.55 V} = AGP 2.0).GVREF is driven by VREFCG on the motherboard.An ADD card pulls the GPAR/ADD_DETECT# pin low and leaves GC_DET# pin unconnected.Since GC_DET# is unconnected, the VREF generator generates an AGP 2.0 compliant voltage,0.75 V to the GVREF pin. This is detected by the VREF voltage comparator, which drives a “live”AGP 3.0 mode detect signal to GPAR (and other AGP I/O buffers), as well as the pull-up/pull-160 Intel ® 82865G/82865GV GMCH Datasheet