AGP Port Design Guidelines
R
172
Intel
®
855PM Chipset Platform Design Guide
Table 39. Layout Routing Guidelines for AGP 2X/4X Signals
Signal
Maximum
Length (inch)
Trace Space
(mils)
(4 mil traces)
Length
Mismatch
(inch)
Relative To
Notes
2X/4X Timing
Domain Set#1
6
8
± 0.1
AGP_ADSTB0 and
AGP_ADSTB0#
AGP_ADSTB0,
AGP_ADSTB0# must
be the same length
(±10 mils)
2X/4X Timing
Domain Set#2
6
8
± 0.1
AGP_ADSTB1 and
AGP_ADSTB1#
AGP_ADSTB1,
AGP_ADSTB1# must
be the same length
(±10 mils)
2X/4X Timing
Domain Set#3
6
8
± 0.1
AGP_SBSTB and
AGP_SBSTB #
AGP_SBSTB,
AGP_SBSTB# must be
the same length (±10
mils)
7.3.2.3.
Trace Length Mismatch Requirements
Table 40. AGP 2.0 Data Lengths Relative to Strobe Length
Max Trace Length
Trace Spacing
Strobe Length
Min Trace Length
Max Trace Length
< 6 in
1:2
X
X – 0.1 in
X + 0.1 in
The trace length minimum and maximum (relative to strobe length) should be applied to each set of
2X/4X timing domain signals
independently
. That is, if AD_STB0 and ADSTB0# are 5 inches, then
AD[15:0] and C/BE[1:0] must be between 4.9 inches and 5.1 inches. However AD_STB1 and
ADSTB1# can be 3.5 inches (and therefore AD[31:16] and C/BE#[3:2] must be between 3.4 inches and
3.6 inches). In addition, all 2X/4X timing domain signals must meet the maximum trace length
requirements.
All signals should be routed as strip lines (inner layers).
All signals in a signal group should be routed on the same layer. Routing studies have shown that
these guidelines can be met. The trace length and trace spacing requirements
must
not be violated
by any signal. Trace length mismatch for all signals within a signal group should be as close to 0
inches as possible to provide optimal timing margin.
Table 41 shows the AGP 2.0 routing summary.
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