Motherboard Layout and Routing Guidelines

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.

Table 2-13. Source Synchronous Motherboard Recommendations

Width:Space

Trace

Line Length

Line Length Matching

 

 

 

 

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

 

 

 

 

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.

Table 2-14. Control Signal Line Length Recommendations

Width:Space

Board

Trace

Line Length

Pull-up Stub Length

 

 

 

 

 

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

 

 

 

 

 

 

 

Some of the control signals require pull-up resistors to be installed on the motherboard. AGP signals must be pulled up to VCC3.3 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.

2.8.2On-board AGP Compliant Device (“Down” Option) Layout Guidelines

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.

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Intel®440GX AGPset Design Guide

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Intel 440GX On-board AGP Compliant Device Down Option Layout Guidelines, Source Synchronous Motherboard Recommendations
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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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