Intel 440GX ユーザーズマニュアル

Motherboard Layout and Routing Guidelines

2-20

Intel

®

 440GX AGPset Design Guide

It is always best to reduce the line length mismatch wherever possible to insure added margin. It is 
also best to separate the traces by as much as possible to reduce the amount of trace to trace 
coupling.

The clock lines on the motherboard can couple with other traces. It is recommended that the clock 
spacing (air gap) be at least two times the trace width to any other traces. It is also strongly 
recommended that the clock spacing be at least four times the trace width to any strobes.

The clock lines on the motherboard need to be simulated to determine the their proper line length. 
The motherboard needs to be designed to the type of clock driver that is being used and 
motherboard trace topology. These clocks need to meet the loading of the receiving device as well 
as the add-in trace length.

Additionally, control signals less than 8.5 inches can be routed 1:1, while control signals greater 
than 8.5 inches should be routed 1:2.

Some of the control signals require pull-up resistors to be installed on the motherboard. AGP 
signals must be pulled up to VCC

3.3

 using 8.2K to 10K pull-up resistors (refer to 

Section 3.5.1, 

“82443GX Interface” on page 3-10

). Pull-up resistors should be discrete resistors, as resistor packs 

will need longer stub lengths and may break timing. The stub to these pull-up resistors needs to be 
controlled. The maximum stub length on a strobe trace is < 0.1 inch. The maximum stub trace 
length on all other traces is < 0.5 inch.

Routing guidelines for the device ‘down’ option are very similar to those when the device is ‘up’. 
Some modifications need to be made when placing the graphics device on the motherboard, due to 
the various trace spacing.

1:1 (Data) / 1:2 (Strobe)

Data / Strobe

1.0 in < line length < 4.5 in

-0.5 in, strobe longest trace

1:2

Data / Strobe

1.0 in < line length < 9.5 in

-0.5 in, strobe longest trace

1:1

Motherboard

Control signals

1.0 in < line length < 8.5 in

< 0.5 in (Strobes < 0.1in)

1:2

Motherboard

Control signals

1.0 in < line length < 10.0 in

< 0.5 in (Strobes < 0.1in)

1:2 (1:4 to Strobe)

Motherboard

Clock