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 VDDQ 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×
1.5 V VDDQ Yes Yes Yes
3.3 V VDDQ Yes Yes No