Agp (4X Mode) Interface Layout And Routing Guidelines; General Layout And Routing Recommendations; Figure 2-45. General Layout Recommendations Of Agp 4X Interface; Table 2-11. Vt82C694X Agp 4X Signal Groups - VIA Technologies Apollo Pro133A Design Manual

Technologies, Inc.
We Connect We Connect

2.4.3 AGP (4X Mode) Interface Layout and Routing Guidelines

This section describes layout and routing guidelines to insure a robust AGP 4X mode interface design. The following guidelines
will help insure that the AGP specification can be met. The system designer should do appropriate analysis and simulation to
verify that the design fulfills AGP specification requirements.

2.4.3.1 General Layout and Routing Recommendations

There are three major groups of AGP control, data and their associated strobe signals listed in Table 2-11. The remaining AGP
signals include AGPVREF (AGP reference voltage input), GCLK and GCLKO (AGP clock input and output), VDDQ/GND
(power/ground) and NCOMP and PCOMP (digital compensation).
AGP Signal Groups
Data / Strobe
Control
Note: The AGP signal naming convention here (and in the VT82C694X datasheet) is slightly different from that in the AGP
Specification.
General routing guidelines for the connections between the VT82C694X chip and the AGP slot are shown in Figure 2-45. These
guidelines were created to give freedom to designs by making tradeoffs between signal coupling and line length. However, AGP
signals must be carefully routed on the motherboard to meet the timing and signal quality requirements of this interface
specification.
Preliminary Revision 0.5, November 19, 1999

Table 2-11. VT82C694X AGP 4X Signal Groups

Group 1: GD[15:0], GBE[1:0]# / GDS0 and GDS0#
Group 2: GD[31:16], GBE[3:2]# / GDS1 and GDS1#
Group 3: SBA[7:0] / SBS and SBS#
GFRM#, GIRDY#, GTRDY#, GSTOP#, GDSEL#, GPIPE#, GRBF#,
ST[2:0], GREQ#, GGNT#, GPAR and GWBF# (14 signals)
AGP 4X
Graphics
Card
AGP Slot
(Universal)
Guidelines:
1. Data and Control (width:Spacing) Routings are (1:3) in the range of 1" < L < 4".
2. Strobe Routings are (1:4) to Strobe and (1:6) to other signals.
3. The recommended motherboard impedance for AGP 4X is 65 ohm +/- 5 ohm.

Figure 2-45. General Layout Recommendations of AGP 4X Interface

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
VT82C694X (4X mode)
Total trace length (L)
(Data, Strobe and Control)
52
VT82C694X
(North Bridge)
Motherboard Design Guidelines