Intel VC820 Design Guide - Page 68
AGP Signal Voltage Tolerance List, 2.7.11 Motherboard / Add-in Card Interoperability
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Layout/Routing Guidelines 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 Card 3.3V Card 1.5V Connector Yes No 3.3V Connector No Yes Universal Connector Yes Yes Table 2-11. Voltage/Data Rate Interoperability 1X 2X 4X 1.5V VDDQ Yes Yes Yes 3.3V VDDQ Yes Yes No 2-42 Intel®820 Chipset Design Guide