Intel 815 - Manual (Page 87)

AGP/Display Cache Design Guidelines
R
Intel
®
815 Chipset Platform Design Guide 87
between them. This pair should be separated from the rest of the AGP signals (and all other
signals) by at least 20 mils (1:4). The strobe pair must be length-matched to less than ±0.1 inch
(i.e., a strobe and its complement must be the same length, within 0.1 inch).
7.3.3 AGP Routing Guideline Considerations and Summary
This section applies to all AGP signals in any motherboard support configuration (e.g., “flexible”
or “AGP only”), as follows:
•
The 2X/4X timing domain signals can be routed with 5-mil spacing, when breaking out of the
GMCH. The routing must widen to the documented requirements, within 0.3 inch of the
GMCH package.
•
When matching trace length for the AGP 4X interface, all traces should be matched from the
ball of the GMCH to the pin on the AGP connector. It is not necessary to compensate for the
lengths of the AGP signals on the GMCH package.
•
Reduce line length mismatch to ensure added margin. Trace length mismatch for all signals
within a signal group should be as close to zero as possible, to provide timing margin.
•
To reduce trace-to-trace coupling (cross-talk), separate the traces as much as possible.
•
All signals in a signal group should be routed on the same layer.
•
The trace length and trace spacing requirements must not be violated by any signal.
Table 22. AGP 2.0 Routing Summary
Signal
Max.
Length
Trace Spacing
(5-mil Traces)
Length
Mismatch
Relative to Notes
1X Timing
Domain 7.5” 4 5 mils No
requirement N/A None
2X/4X Timing
Domain Set 1 7.25” 4 20 mils ±0.125” AD_STB0
and
AD_STB0#
AD_STB0,
AD_STB0# must be
the same length
2X/4X Timing
Domain Set 2 7.25” 4 20 mils ±0.125” AD_STB1
and
AD_STB1#
AD_STB1,
AD_STB1# must be
the same length
2X/4X Timing
Domain Set 3 7.25” 4 20 mils ±0.125” SB_STB and
SB_STB#
SB_STB, SB_STB#
must be the same
length
2X/4X Timing
Domain Set 1 6” 3 15 mils 1 ±0.5” AD_STB0
and
AD_STB0# AD_STB0,
AD_STB0# must be
the same length
2X/4X Timing
Domain Set 2 6” 3 15 mils 1 ±0.5” AD_STB1
and
AD_STB1# AD_STB1,
AD_STB1# must be
the same length
2X/4X Timing
Domain Set 3 6” 3 15 mils 1 ±0.5” SB_STB and
SB_STB#
SB_STB, SB_STB#
must be the same
length
NOTES:
1. Each strobe pair must be separated from other signals by at least 20 mils.
2. These guidelines apply to board stack-ups with 15% impedance tolerance.
3. 4 inches is the maximum length for a flexible motherboards.
4. Solution valid for AGP-only motherboards.