User's Manual

Layout/Routing Guidelines
2-42 Intel
®
820 Chipset Design Guide
2.7.10.1 AGP Signal Voltage Tolerance List
The following signals on the AGP interface are 3.3V tolerant during 1.5V operation:
•
PME#
•
INTA#
•
INTB#
•
GPERR#
•
GSERR#
•
CLK
•
RST
The following signals on the AGP interface are 5V tolerant (refer to the USB specification):
•
USB+
•
USB-
•
OVRCNT#
The following signal is a special AGP signal. It is either Grounded or No Connected on an AGP
card.
•
TYPEDET#
Note: All other signals on the AGP interface are in the VDDQ group. They are not 3.3V tolerant
during 1.5V AGP operation.
2.7.11 Motherboard / Add-in Card Interoperability
Currently, there are three AGP connectors:
•
3.3V AGP connector
•
1.5V AGP connector
•
Universal AGP connector.
To maximize add-in flexibility, implementing the universal connector in Intel
®
820 chipset based
system is strongly recommended. All add-in cards are either 3.3V or 1.5V cards. Due to timings,
4X transfers at 3.3V are not allowed.
Table 2-10. Connector/Add-in Card Interoperability
1.5V Connector 3.3V Connector Universal Connector
1.5V Card Yes No Yes
3.3V Card No Yes Yes
Table 2-11. Voltage/Data Rate Interoperability
1X 2X 4X
1.5V VDDQ Yes Yes Yes
3.3V VDDQ Yes Yes No