Motherboard Layout and Routing Guidelines

2.8AGP Layout and Routing Guidelines

For the definition of AGP Interface functionality (protocols, rules and signaling mechanisms, as well as the platform level aspects of AGP functionality), refer to the latest AGP Interface Specification rev 1.0 and the AGP Platform Design Guide. These documents focus only on specific Intel® 440GX AGPset platform recommendations for the AGP interface.

In this document the term “data” refers to AD[31:0], C/BE[3:0]# and SAB[7:0]. The term “strobe” refers to AD_STB[1:0] and SB_STB. When the term data is used, it is referring to one of three groups of data as seen in Table 2-12. When the term strobe is used it is referring to one of the three strobes as it relates to the data in its associated group.

Table 2-12. Data and Associated Strobe

Data

Associated Strobe

 

 

AD[15:0] and C/BE[1:0]#

AD_STB0

 

 

AD[31:16] and C/BE[3:2]#

AD_STB1

 

 

SBA[7:0]

SB_STB

 

 

2.8.1AGP Connector (“Up Option) Layout Guidelines

The maximum line length is dependent on the routing rules used on the motherboard. These routing rules were created to give freedom for designs by making trade-offs between signal coupling (trace spacing) and line lengths. These routing rules are divided by trace spacing. In 1:1 spacing, the distance between the traces (air gap) is the same as the -width of the trace. In 1:2 spacing, the distance between the traces is twice the width of the trace.

Figure 2-14. AGP Connector Layout Guidelines

AGP

Compliant

Graphics

Device

Always 1:2 Strobe Routing

AGP Signal Bundle

82443GX

1.0” - 4.5” 1:1 (Data) Routing

4.5” - 9.5” 1:2 (Data) Routing

AGP

Connector

For trace lengths that are between 1.0 inch and 4.5 inches, a 1:1 trace spacing is recommended for data lines. The strobe requires a 1:2 trace spacing. This is for designs that require less than 4.5 inches between the AGP connector and the AGP target.

Longer lines have more crosstalk. Therefore, to maintain skew, longer line lengths require a greater amount of spacing between traces. For line lengths greater than 4.5” and less than 9.5”, 1:2 routing is recommended for all data lines as well as the strobes. For all designs, the line length mismatch must be less than 0.5” and the strobe must be the longest signal of the group.

Intel®440GX AGPset Design Guide

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Intel 440GX manual AGP Layout and Routing Guidelines, AGP Connector Up Option Layout Guidelines, Data and Associated Strobe
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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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