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Intel
®
820E Chipset
R
Design Guide 71
2.8.10.1. AGP Signal Voltage Tolerance List
The following signals on the AGP interface are 3.3 V tolerant during a 1.5 V operation:
• PME#
• INTA#
• INTB#
• GPERR#
• GSERR#
• CLK
• RST
The following signals on the AGP interface are 5 V tolerant (refer to the USB specification):
• USB+
• USB-
• OVRCNT#
The following signal is a special AGP signal, which is either grounded or not connected on an AGP card.
• TYPEDET#
Note: All other signals on the AGP interface are in the V
DDQ
group. They are not 3.3 V tolerant during a 1.5 V
AGP operation.
2.8.11. Motherboard / Add-in Card Interoperability
Currently, there are three AGP connectors:
• 3.3 V AGP connector
• 1.5 V AGP connector
• Universal AGP connector.
To maximize add-in flexibility, it is highly advisable to implement the universal connector in an Intel
820E chipset-based system. All add-in cards are either 3.3 V or 1.5 V cards. Due to timings, 4× transfers
at 3.3 V are not allowed.
Table 13. Connector / Add-in Card Interoperability
1.5 V Connector 3.3 V Connector Universal Connector
1.5 V card Yes No Yes
3.3 V card No Yes Yes
Table 14. Voltage / Data Rate Interoperability
1× 2× 4×
1.5 V V
DDQ
Yes Yes Yes
3.3 V V
DDQ
Yes Yes No