my half-functional agp 4x - 2x adapter..

hanksemenec · 08 January 2007, 05:59:06

AGP VDDQ pins supply voltage to the AGP IO pins. When the card is inserted and power is applied, mother board and the GFX card auto negotiate for the right voltage to be applied to the North Bridge IO and the GFX IO.

If one side is running 1.5V and the other is set to 3.3V you can create a very smelly problem. 3.3V system signals will overdrive the 1.5V system and the protection diodes, tied to 1.5V system at every IO cell, will start dumping all the extra energy to 1.5V rail. TYPEDET# pin informs the system about the voltage to use. 4X AGP cards tie the pin low, 2x and 1x AGP cards leave the pin open.

IF 1.5V rail IO is talking to 3.3V IO the voltage swing is not sufficient to cross the thresh-hold on the 3.3V IO and high level will not be recognized.

3.3V thresh-hold for VSA 100 IO is set to 1/2 VDDQ. 1.5V system required thresh-hold a little higher then 1/2 VDDQ, so another pin was added to provide the reference value to VSA 100 IO cells. Comparator anlong with TYPEDET# value (high or low) will select the proper voltage reference. Voltage reference is a resistor divider, tied between VDDQ and GND, with capacitor bypass to GND to reject high frequency noise.

Another reason, why a separate voltage plane is required for IO is signal path return. The return current on the high speed trace runs directly under the trace to the driving output cell. It will run on GND plane or VDDQ plane. If you provide a separate IO power, the return current has to find another path to the out put cell, that breaks the impedance of the trace and distorts the signal. The return current has to find a capacitor to GND plane, but if the place is not right next to the high speed trace it will break the impedance, whigh would be set to about 68 ohms by trace dimesion and plane separation.

Welcome to the wanderfull world of Signal Integrity (SI).

Hank

IceFire · 08 January 2007, 20:27:52

thanks, hank...

i did not understand everything... ^^

even through you said that the board will be damaged after some time,i still will try my adapter with some old matrox g200 agp and some cheap agp 8x motherboards...
you told us that the TYPEDET pins is needed for the voltage configuration. but i know about some newer agp 4x/8x cards, that work with agp 4/8x (some geforce 2 models) even through the TYPEDET pin is not connected. some pages says that this pin is only checked in agp universal boards, on whose the geforce runs at 3,3V...
do u know whitch pins have to be modified to set the agp signal level to 3,3V? i think it is dependent on the vref pin, but i don't know which design concept i have to use...
if i would plug my adapter (with this agp 2x resistor divider) into a agp 8x board, do u know witch VDDQ i have to use? the replaced 3,3V VDDQ or the original 1,5V VDDQ of the motherboard? the vref pin is 66A, am i right?

but it would be much more easier to modify a v5 to support the 1,5V signal level..
if u know what to do, tell me and i will try it on my voodoo5 ^^!

m14radu · 04 May 2007, 23:53:55

Hey IceFire,

Any good news related to this adapter ?
How is the Projekt working ?

Br.
Radu.

IceFire · 03 June 2007, 17:54:54

Sorry, project was suspended,
any change will be announced here.

Xasd · 04 June 2007, 10:09:24

This is not good news, but if you find some information of how to make it, please post it. It can help us to continue the project.

If I have time, this summer i'll try to make it with an old graphic card

m14radu · 28 June 2007, 17:00:35

Hey IceFire !

Take a closer look here:
http://www.forumzone.it/topic.asp?TOPIC_ID=22932&FORUM_ID=40&CAT_ID=25&Topic_Title=3DFX+V5+5500+Agp+Mod+%26+AN7+AGP2x+Mod+%26+V%2DAGP+Mod%2E&Forum_Title=3dfx+Hardware+e+Software+%2D+Discussioni
It looks like somebody did the mod succesfully !
Unfortunately it's in italian language, but maybe somebody can translate it !

Br.
Radu.

IceFire · 19 July 2007, 22:42:55

tried the modification on my i875p board....

now, the agp bus is dead^^
damn.. :/

well, when i got some more time, i will buy a second agp riser and a new agp 8x board and do the same modifications again... i might made a mistake...

maybe the nforce2 has very powerful agp power regulators. i will also buy abit an7 & check my adapter there.

it would be greaaatt success if this modification would finally run with no problems.

m14radu · 20 July 2007, 06:37:46

Hi,

Sorry for your board. Did you cut the voodoo5 card or you modify the AGP slot ?
Did u supply with 3.3V the AGP Slot, or you tried to start directly, with the default 1.65 Voltage ?
Please post some details, about your experience.
Did the card post for short time ?
How it's behave exactly ?

Radu.

IceFire · 21 July 2007, 17:12:10

i tried to supply the 3,3v to the agp pin A34 - its almost the same thing i've done with my agp riser card... but on the riser card, i disconnected some more lanes from the agp and connected them to 3,3V.....now, i connected the pin to the pin on the motherboard and supplied 3,3V there. it did not work :/
maybe i've made a mistake. i will try again soon!
€dit: the i875p board will now get a voodoo banshee pci

€dit2:
how about this little thing here:
http://cgi.ebay.de/Apple-Macintosh-Cube-AGP-riser-New_W0QQitemZ230062944024QQihZ013QQcategoryZ19521QQrdZ1QQssPageNameZWD1VQQcmdZViewItem
it might work with voodoos

someone want to buy one and test it?

max1024 · 22 July 2007, 18:38:06

Can somebody tell me about this devise, I found it foto on one of the japanese sites. It's a PCI to AGP bridge, if smb use it or can it work with agp voodoos ?

m14radu · 24 July 2007, 21:08:56

@Icefire

Check out this Projekt !
http://www.falconfly-central.de/cgi-bin/yabb/YaBB.pl?board=general;action=display;num=1185303152

Regards.
Radu.

max1024 · 24 July 2007, 21:53:35

m14radu
Excellent, superb, fantastic & cool. You make a Great work! my congratulations

It would be to friend AGP voodoo with pci

IceFire · 25 July 2007, 13:55:11

wow, nice done

gratulations!
i already bought a new agp riser card cause i don't want to cut my v5

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&ih=018&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=280132054387&rd=1&rd=1

and you did not connect any wire at all?

it's time 4 new world records

AMD 64 + Voodoo5

ggab · 25 July 2007, 14:35:02

go on this thread:
www.3dfxzone.it/enboard/topic.asp?TOPIC_ID=6626

bye *_*

m14radu · 29 July 2007, 15:58:12

@ Icefire

Do u have an half-functioning Voodoo5 card.
U have removed afaik the second chip becouse of malfunction.
Can u please check the traces for TYPEDET Pin ( Location is C1 ) ?
I need a soldering point for that Pin. I find already one, can u please check and confirm this ?

See the entyre thread here:

http://www.falconfly-central.de/cgi-bin/yabb/YaBB.pl?board=general;action=display;num=1185303152

P.S. Could u check if there is a short between AVR15 and AVR30
( Pin Location is P2 and P3 according to Napalm Databook ) ?

I need this information in order to go on !
Thanks.

Radu.

Notice ~

my half-functional agp 4x - 2x adapter..