Motherboard Layout and Routing Guidelines

2.9.6.3PCI Clock Layout

PCI clock nets should be routed a point-to-point connections with a 22 Ohm series resistor that is to be placed as close to the output pins on the clock driver as possible (<0.5”). Layout guidelines: Match trace lengths to the longest trace.

Net

Trace length

min

max

Substrate

 

 

 

 

 

 

 

 

 

 

Clock chip - PCI connector

H + 4.8”

1.0”

12.5”

2.5”

 

 

 

 

 

Clock chip - PIIX4E

H + 7.3”

1.0”

15.0”

NA

 

 

 

 

 

Clock chip -440GX

H + 7.3”

1.0”

15.0”

NA

 

 

 

 

 

2.9.6.4SDRAM Clock Layout

Series Termination: No series termination is required for the SDRAM clocks between the CKBF and the DIMMs. For DCLKO (between 82443GX and CKBF), two termination resistors are required: A 22 Ohm series resistor located at the driver, and a 47 Ohm series resistor located at the receiver.

Layout guidelines:

Net

Trace Length

Min

Max

Cap

 

 

 

 

 

 

 

 

 

 

440GX - CKBF (DLKO)

NA

1.0”

10.0”

NA

 

 

 

 

 

CKBF - DIMM (SDRAM Clocks)

A

1.0”

3.0”

NA

 

 

 

 

 

CKBF - 82443GX (DCLKWR)

A+2.5”

3.5”5.5”

 

20pF

 

 

 

 

 

Note: A single clock output from CKBF is used to drive DCLKWR at the 82443GX. The single clock net should be “T”d as close as possible to the 82443GX. An additional capacitive load of 20pF is also required. The capacitor should also be located as close to the 82443GX as possible.

The 82443GX does not have an internal connection for pin AB22. Existing designs connected DCLKWR & AB22 nets on the motherboard. Since the 82443GX does not have an internal connection for pin AB22, it will cause a slightly reduced load capacitance on the net. To avoid additional clock skew on existing designs, a discrete capacitor larger than the 20pF capacitor recommended may be required.

Intel®440GX AGPset Design Guide

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Image 57
Intel manual PCI Clock Layout, Sdram Clock Layout, Net Trace Length Min Max Cap, 440GX Ckbf Dlko, Ckbf 82443GX Dclkwr
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440GX specifications

The Intel 440GX chipset was launched in 1997 as part of Intel's series of chipsets known as the 440 family, and it served as a critical component for various Pentium II and Pentium III-based motherboard architectures. Specifically designed for the second generation of Intel’s processors, the 440GX delivered enhanced performance and supported a range of important technologies that defined PC architectures of its time.

One of the main features of the Intel 440GX was its support for a 100 MHz front-side bus (FSB), which significantly improved data transfer rates between the CPU and the memory subsystem. This advancement allowed the 440GX to accommodate both the original Pentium II processors as well as the later Pentium III chips, providing compatibility and flexibility for system builders and consumers alike.

The 440GX chipset included an integrated AGP (Accelerated Graphics Port) controller, which supported AGP 2x speeds. This enabled high-performance graphics cards to be utilized effectively, delivering many enhanced graphics capabilities for gaming and multimedia applications. The AGP interface was crucial at the time as it offered a dedicated pathway for graphics data, increasing bandwidth compared to traditional PCI slots.

In terms of memory support, the 440GX could address up to 512 MB of SDRAM, allowing systems built with this chipset to run comfortably with sufficient memory for the era’s demanding applications. The memory controller was capable of supporting both single and double-sided DIMMs, which provided versatility in memory configuration for system builders.

Another notable feature of the Intel 440GX was its support for multi-processor configurations through its Dual Processors support feature. This allowed enterprise and workstation computers to leverage the performance advantages of multiple CPUs, making the chipset suitable for business and professional environments where multitasking and high-performance computing were essential.

On the connectivity front, the chipset supported up to six PCI slots, enhancing peripheral device integration and expansion capabilities. It also included integrated IDE controllers, facilitating connections for hard drives and CD-ROM devices.

Overall, the Intel 440GX chipset represented a balanced combination of performance, flexibility, and technology advancements for its time. Its introduction helped establish a foundation for subsequent advancements in PC technology and set the stage for more powerful computing systems in the years to come.
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