Intel 815 - Manual (Page 83)

AGP/Display Cache Design Guidelines
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Intel
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815 Chipset Platform Design Guide 83
7.2.1 AGP Interface Signal Groups
The signals on the AGP interface are broken into three groups: 1X timing domain signals, 2X/4X
timing domain signals, and miscellaneous signals. Each group has different routing requirements.
In addition, within the 2X/4X timing domain signals, there are three sets of signals. All signals in
the 2X/4X timing domain must meet minimum and maximum trace length requirements as well as
trace width and spacing requirements. However, trace length matching requirements only need to
be met within each set of 2X/4X timing domain signals. The signal groups are listed in Table 20.
Table 20. AGP 2.0 Signal Groups
Group Signal
1X timing domain • CLK (3.3V), RBF#, WBF#, ST[2:0], PIPE#, REQ#, GNT#, PAR,
FRAME#, IRDY#, TRDY#, STOP#, DEVSEL#
2X / 4X timing domain •
Set #1 : AD[15:0], C/BE[1:0]#, AD_STB0, AD_STB0#1 1
•
Set #2 : AD[31:16], C/BE[3:2]#, AD_STB1, AD_STB1# 1
•
Set #3 : SBA[7:0], SB_STB, SB_STB#1
Miscellaneous, async • USB+, USB-, OVRCNT#, PME#, TYPDET#, PERR#, SERR#, INTA#,
INTB#
NOTES:
1. These signals are used in 4X AGP mode ONLY.
Table 21. AGP 2.0 Data/Strobe Associations
Data Associated Strobe in 1X Associated
Strobe in 2X
Associated
Strobes in 4X
AD[15:0] and C/BE[1:0]# Strobes are not used in 1X mode.
All data is sampled on rising clock
edges. AD_STB0 AD_STB0,
AD_STB0#
AD[31:16] and C/BE[3:2]# Strobes are not used in 1X mode.
All data is sampled on rising clock
edges. AD_STB1 AD_STB1,
AD_STB1#
SBA[7:0] Strobes are not used in 1X mode.
All data is sampled on rising clock
edges. SB_STB SB_STB,
SB_STB#
Throughout this section, the term data refers to AD[31:0], C/BE[3:0]#, and SBA[7:0]. The term
strobe refers to AD_STB[1:0], AD_STB[1:0]#, SB_STB, and SB_STB#. When the term data is
used, it refers to one of the three sets of data signals, as listed in Table 21. When the term strobe is
used, it refers to one of the strobes as it relates to the data in its associated group.
The routing guidelines for each group of signals (1X timing domain signals, 2X/4X timing domain
signals, and miscellaneous signals) will be addressed separately.