2 board description – Intel 440GX User Manual

Page 27

Intel

440GX AGPset Design Guide

2-3

Motherboard Layout and Routing Guidelines

NLX Form Factor:

1. The NLX placement and layout below is recommended for a single (UP) Intel

Pentium

processor / Intel

440GX AGPset system design.

2. The example placement below shows one Slot 1 connector, 4 DIMM sockets, and an AGP

compliant device down.

3. For an NLX form factor design, the AGP compliant graphics device may readily be integrated

on the motherboard (device down option).

4. The trace length limitation between critical connections will be addressed later in this

document.

Figure 2-3

is for reference only and the trade-off between the number of DIMM sockets, and

other motherboard peripherals need to be evaluated for each design.

2.2

Board Description

For a single processor / Intel

440GX AGPset motherboard design, a 4 layer stack-up arrangement

is recommended. The stack up of the board is shown in

Figure 2-4

. The impedance of all the signal

layers are to be between 50 and 80 ohms. Lower trace impedance will reduce signal edge rates,
over & undershoot, and have less cross-talk than higher trace impedance. Higher trace impedance
will increase edge rates and may slightly decrease signal flight times.

Figure 2-3. Example NLX Placement for a UP Intel

Pentium

processor / Intel

440GX

Design

82443GX

PIIX4E

AGP

Pentium

Slot 1

I/O Ports

SDRAM DIMMs

PCI0/ISA Riser

CK100

C K B F

v 0 0 3

Host Interface

PCI Interface

AGP Interface

S D R A M

Interface