Intel 440GX manual AGP Layout and Routing Guidelines, AGP Connector “Up Option Layout Guidelines

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 2-19