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Design Guide 

 

71 

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. 

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. 

1.5 V card 

Yes 

No 

Yes 

3.3 V card 

No 

Yes 

Yes 

1.5 V V

DDQ

 Yes 

Yes 

Yes 

3.3 V V

DDQ

 Yes 

Yes 

No