A7N8X-X and AGP confusion (by me)

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mike

I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for it. The
mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V only" bit that's
bothering me.

It implies (to me anyway) that there's more than one voltage for AGP 8X (AGP
version 3.0).

From the web I found this... (with my interruptions),

"The bottomline is that your 8X video card can theoretically be safely TESTED in
any 1.5V motherboard for compatibility."

That seems to mean that 8X/ 1.5V is NOT the norm for AGP 3.0!


"But if you know for a fact that your board only runs 1.5V AGP 2.0 spec and your
8X AGP 3.0 card runs only 0.8v spec,..."

So AGP 3.0 can run 1.5 OR 0.8 depending on the particular card?

"...then the two should NOT be compatible one another. At the very least it will
be unstable, if it runs at all. However, we've had a lot of users tell us that
their AGP 8x cards work on 4x only motherboards. This is likely due to the fact
that some AGP8X video cards are in fact universal 1.5V capable AGP3.0 cards that
can run on either 1.5V or 0.8V (remember, AGP speeds are backwards compatible,
only voltage incompatibilies cause problems)."


Confused? I certainly am. Can someone PLEASE tell me what AGP 3.0 1.5V card I
may use in this mobo?

many tia
 
I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for it. The
mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V only" bit that's
bothering me.

It implies (to me anyway) that there's more than one voltage for AGP 8X (AGP
version 3.0).

From the web I found this... (with my interruptions),

"The bottomline is that your 8X video card can theoretically be safely TESTED in
any 1.5V motherboard for compatibility."

That seems to mean that 8X/ 1.5V is NOT the norm for AGP 3.0!


"But if you know for a fact that your board only runs 1.5V AGP 2.0 spec and your
8X AGP 3.0 card runs only 0.8v spec,..."

So AGP 3.0 can run 1.5 OR 0.8 depending on the particular card?

"...then the two should NOT be compatible one another. At the very least it will
be unstable, if it runs at all. However, we've had a lot of users tell us that
their AGP 8x cards work on 4x only motherboards. This is likely due to the fact
that some AGP8X video cards are in fact universal 1.5V capable AGP3.0 cards that
can run on either 1.5V or 0.8V (remember, AGP speeds are backwards compatible,
only voltage incompatibilies cause problems)."


Confused? I certainly am. Can someone PLEASE tell me what AGP 3.0 1.5V card I
may use in this mobo?

many tia
Click to expand...


If you are looking at ATI cards, this may help...
http://www.ati.com/support/faq/agpchart.html

Ed
 
mike said:
I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for
it. The mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V
only" bit that's bothering me.

It implies (to me anyway) that there's more than one voltage for
AGP 8X (AGP version 3.0).

From the web I found this... (with my interruptions),

"The bottomline is that your 8X video card can theoretically be
safely TESTED in any 1.5V motherboard for compatibility."

That seems to mean that 8X/ 1.5V is NOT the norm for AGP 3.0!

"But if you know for a fact that your board only runs 1.5V AGP
2.0 spec and your 8X AGP 3.0 card runs only 0.8v spec,..."

So AGP 3.0 can run 1.5 OR 0.8 depending on the particular card?

"...then the two should NOT be compatible one another. At the
very least it will be unstable, if it runs at all. However, we've
had a lot of users tell us that their AGP 8x cards work on 4x
only motherboards. This is likely due to the fact that some AGP8X
video cards are in fact universal 1.5V capable AGP3.0 cards that
can run on either 1.5V or 0.8V (remember, AGP speeds are backwards
compatible, only voltage incompatibilies cause problems)."

Confused? I certainly am. Can someone PLEASE tell me what AGP 3.0
1.5V card I may use in this mobo?

many tia
Click to expand...

******
Generally, I recommend mixing "like with like". If you have an
AGP 8X motherboard, find an AGP 8X video card to go with it.
A 4X motherboard goes with a 4X video card. The reason for this,
is it maximizes the overlap of possible speed settings. Mixing
vastly different cards and motherboards, causes problems when
you need to slow the AGP interface, and the required setting
is not common to both piece of hardware.

In the AGP 2.0 spec, the AGP speed is a three bit wide field.
If all three bits are set, then all three speeds are supported.

"RATE The RATE field indicates the data transfer rates supported
by this device. A.G.P. devices must report all that apply.
Bit Set Transfer Rate
0 1X
1 2X
2 4X

In the AGP 3.0 spec, the AGP speed is a four bit wide field.
Notice the patterns used to indicate 4X, 8X or both.

AGPSTAT[3] Code Speed Supported
0 xxx See AGP2.0 Specs
1 001 4x
1 010 8x
1 011 4x, and 8x
1 All other codes Reserved

Now, what happens when an 8X AGP 3.0 card is stuffed in an
AGP 2.0 motherboard ? The motherboard only has a three bit
status field, so ignores AGPSTAT[3]. The video card looks
like it supports only 2X and 1X. If the BIOS sets the slot
to 2X, chances are the screen will go black! 2X is not
supported by the video card. That is why I recommend mixing
"like with like".

In your case, find an AGP 8X card to go with your 8X motherboard.
*****

As far as that mumbo-jumbo you copy/pasted above, there are
only two I/O pad supply voltages. They are 3.3V and 1.5V. These
voltages are fed to the I/O pins on the GPU and the I/O
pins on the Northbridge. The TYPEDET# pin indicates the
voltage the video card would prefer, even if it can handle
more than one voltage. A video card grounding TYPEDET# indicates
the card would prefer 1.5V. The slots cut in the card edge, encode
whether the card is compatible with 1.5, 3.3V, or both kinds
of motherboards.

So, where does 0.8V come from ? The 0.8V is an _I/O signal level_
rather than an I/O supply voltage. The pad driver is powered by
1.5V. If a series damped termination type is used (AGP 2.0), the
signal level at the end of the bus is 1.5V. That would be suitable
for AGP 4X or slower. To reach the 8X rates, the end of the bus
is parallel terminated inside the chip. The parallel termination
causes a voltage divider action, so the height of the signal seen
on the AGP slot connector measures only 0.8V high.

What this means is, the I/O pads are not powered by 0.8V, they
receive power from 1.5V in both cases.

There is a lot that is unstated, when it comes to the actual
implementation of the silicon. The standard doesn't dictate
how certain things are done, or what combinations of features
are supported. For example, if the parallel terminations at
the end of the bus, can be turned on and off, that would give
the ability for a card to be universal.

http://mirror.ati.com/support/faq/agpchart.html
http://www.ati.com/support/agpchart/agp.html

On the first web page, there are no 0.8V I/O only cards.
They are always 1.5/0.8. There are plenty of older 3.3V only
cards, and those are the ones to avoid.

It would be pretty hard to make a driver that runs from 0.8V
and can drive a parallel termination.

When you buy an 8X card, it generally supports 8X and 4X, as
AGP tries to be backward compatible. 2X is not supported,
as there is no code point in the status register for it.
Why they didn't make the AGP speed field 5 bits wide, I'll
never know.

HTH,
Paul
 
mike said:
I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for
it. The mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V
only" bit that's bothering me.
Click to expand...
[..............]

When you buy an 8X card, it generally supports 8X and 4X, as
AGP tries to be backward compatible. 2X is not supported,
as there is no code point in the status register for it.
Why they didn't make the AGP speed field 5 bits wide, I'll
never know.

HTH,
Paul
Click to expand...

Thanks for the responses and for this excellent description. Would you mind if I
posted a copy on uk.comp.homebuilt? I'm sure I'm not the only one your
description would help. (Will attribute to you of course).
 
I was thinking of this board for a replacement to my KT7 raid. I have a
Diamond Viper 550. Would this video card work with the A7N8X-X motherboard,
and what voltage is the Viper 550?

thanks




Paul said:
mike said:
I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for
it. The mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V
only" bit that's bothering me.

It implies (to me anyway) that there's more than one voltage for
AGP 8X (AGP version 3.0).

From the web I found this... (with my interruptions),

"The bottomline is that your 8X video card can theoretically be
safely TESTED in any 1.5V motherboard for compatibility."

That seems to mean that 8X/ 1.5V is NOT the norm for AGP 3.0!

"But if you know for a fact that your board only runs 1.5V AGP
2.0 spec and your 8X AGP 3.0 card runs only 0.8v spec,..."

So AGP 3.0 can run 1.5 OR 0.8 depending on the particular card?

"...then the two should NOT be compatible one another. At the
very least it will be unstable, if it runs at all. However, we've
had a lot of users tell us that their AGP 8x cards work on 4x
only motherboards. This is likely due to the fact that some AGP8X
video cards are in fact universal 1.5V capable AGP3.0 cards that
can run on either 1.5V or 0.8V (remember, AGP speeds are backwards
compatible, only voltage incompatibilies cause problems)."

Confused? I certainly am. Can someone PLEASE tell me what AGP 3.0
1.5V card I may use in this mobo?

many tia
Click to expand...

******
Generally, I recommend mixing "like with like". If you have an
AGP 8X motherboard, find an AGP 8X video card to go with it.
A 4X motherboard goes with a 4X video card. The reason for this,
is it maximizes the overlap of possible speed settings. Mixing
vastly different cards and motherboards, causes problems when
you need to slow the AGP interface, and the required setting
is not common to both piece of hardware.

In the AGP 2.0 spec, the AGP speed is a three bit wide field.
If all three bits are set, then all three speeds are supported.

"RATE The RATE field indicates the data transfer rates supported
by this device. A.G.P. devices must report all that apply.
Bit Set Transfer Rate
0 1X
1 2X
2 4X

In the AGP 3.0 spec, the AGP speed is a four bit wide field.
Notice the patterns used to indicate 4X, 8X or both.

AGPSTAT[3] Code Speed Supported
0 xxx See AGP2.0 Specs
1 001 4x
1 010 8x
1 011 4x, and 8x
1 All other codes Reserved

Now, what happens when an 8X AGP 3.0 card is stuffed in an
AGP 2.0 motherboard ? The motherboard only has a three bit
status field, so ignores AGPSTAT[3]. The video card looks
like it supports only 2X and 1X. If the BIOS sets the slot
to 2X, chances are the screen will go black! 2X is not
supported by the video card. That is why I recommend mixing
"like with like".

In your case, find an AGP 8X card to go with your 8X motherboard.
*****

As far as that mumbo-jumbo you copy/pasted above, there are
only two I/O pad supply voltages. They are 3.3V and 1.5V. These
voltages are fed to the I/O pins on the GPU and the I/O
pins on the Northbridge. The TYPEDET# pin indicates the
voltage the video card would prefer, even if it can handle
more than one voltage. A video card grounding TYPEDET# indicates
the card would prefer 1.5V. The slots cut in the card edge, encode
whether the card is compatible with 1.5, 3.3V, or both kinds
of motherboards.

So, where does 0.8V come from ? The 0.8V is an _I/O signal level_
rather than an I/O supply voltage. The pad driver is powered by
1.5V. If a series damped termination type is used (AGP 2.0), the
signal level at the end of the bus is 1.5V. That would be suitable
for AGP 4X or slower. To reach the 8X rates, the end of the bus
is parallel terminated inside the chip. The parallel termination
causes a voltage divider action, so the height of the signal seen
on the AGP slot connector measures only 0.8V high.

What this means is, the I/O pads are not powered by 0.8V, they
receive power from 1.5V in both cases.

There is a lot that is unstated, when it comes to the actual
implementation of the silicon. The standard doesn't dictate
how certain things are done, or what combinations of features
are supported. For example, if the parallel terminations at
the end of the bus, can be turned on and off, that would give
the ability for a card to be universal.

http://mirror.ati.com/support/faq/agpchart.html
http://www.ati.com/support/agpchart/agp.html

On the first web page, there are no 0.8V I/O only cards.
They are always 1.5/0.8. There are plenty of older 3.3V only
cards, and those are the ones to avoid.

It would be pretty hard to make a driver that runs from 0.8V
and can drive a parallel termination.

When you buy an 8X card, it generally supports 8X and 4X, as
AGP tries to be backward compatible. 2X is not supported,
as there is no code point in the status register for it.
Why they didn't make the AGP speed field 5 bits wide, I'll
never know.

HTH,
Paul
Click to expand...
 
"George" said:
I was thinking of this board for a replacement to my KT7 raid. I have a
Diamond Viper 550. Would this video card work with the A7N8X-X motherboard,
and what voltage is the Viper 550?

thanks
Click to expand...
I found a picture here of a Viper 550:

http://www.hardwareportal.ru/Video/Rivatnt.chip/index.html -->
http://www.hardwareportal.ru/Video/Rivatnt.chip/Viper550.jpg

It looks like the card has a slot cut only for 3.3V. The card
should not fit (not be insertable) in the A7N8X-X motherboard,
as it has a key in the 1.5V position, and the video card has
to have a matching slot in its connector, which the TNT won't
have.

The pictures at the bottom of this page illustrate keying:
http://mirror.ati.com/support/faq/agpchart.html

An FX5200 is a nice low power alternative. Some FX5200 cards
are fanless, so shouldn't crush your power supply, or overheat
the computer case. It has about 6X the triangle rate of your
TNT card.

HTH,
Paul
Paul said:
mike said:
I'm getting an Asus A7N8X-X mobo and looking for a AGP video card for
it. The mobo spec says "1 x AGP 8X (1.5V only)." and it's the "1.5V
only" bit that's bothering me.

It implies (to me anyway) that there's more than one voltage for
AGP 8X (AGP version 3.0).

From the web I found this... (with my interruptions),

"The bottomline is that your 8X video card can theoretically be
safely TESTED in any 1.5V motherboard for compatibility."

That seems to mean that 8X/ 1.5V is NOT the norm for AGP 3.0!

"But if you know for a fact that your board only runs 1.5V AGP
2.0 spec and your 8X AGP 3.0 card runs only 0.8v spec,..."

So AGP 3.0 can run 1.5 OR 0.8 depending on the particular card?

"...then the two should NOT be compatible one another. At the
very least it will be unstable, if it runs at all. However, we've
had a lot of users tell us that their AGP 8x cards work on 4x
only motherboards. This is likely due to the fact that some AGP8X
video cards are in fact universal 1.5V capable AGP3.0 cards that
can run on either 1.5V or 0.8V (remember, AGP speeds are backwards
compatible, only voltage incompatibilies cause problems)."

Confused? I certainly am. Can someone PLEASE tell me what AGP 3.0
1.5V card I may use in this mobo?

many tia
Click to expand...

******
Generally, I recommend mixing "like with like". If you have an
AGP 8X motherboard, find an AGP 8X video card to go with it.
A 4X motherboard goes with a 4X video card. The reason for this,
is it maximizes the overlap of possible speed settings. Mixing
vastly different cards and motherboards, causes problems when
you need to slow the AGP interface, and the required setting
is not common to both piece of hardware.

In the AGP 2.0 spec, the AGP speed is a three bit wide field.
If all three bits are set, then all three speeds are supported.

"RATE The RATE field indicates the data transfer rates supported
by this device. A.G.P. devices must report all that apply.
Bit Set Transfer Rate
0 1X
1 2X
2 4X

In the AGP 3.0 spec, the AGP speed is a four bit wide field.
Notice the patterns used to indicate 4X, 8X or both.

AGPSTAT[3] Code Speed Supported
0 xxx See AGP2.0 Specs
1 001 4x
1 010 8x
1 011 4x, and 8x
1 All other codes Reserved

Now, what happens when an 8X AGP 3.0 card is stuffed in an
AGP 2.0 motherboard ? The motherboard only has a three bit
status field, so ignores AGPSTAT[3]. The video card looks
like it supports only 2X and 1X. If the BIOS sets the slot
to 2X, chances are the screen will go black! 2X is not
supported by the video card. That is why I recommend mixing
"like with like".

In your case, find an AGP 8X card to go with your 8X motherboard.
*****

As far as that mumbo-jumbo you copy/pasted above, there are
only two I/O pad supply voltages. They are 3.3V and 1.5V. These
voltages are fed to the I/O pins on the GPU and the I/O
pins on the Northbridge. The TYPEDET# pin indicates the
voltage the video card would prefer, even if it can handle
more than one voltage. A video card grounding TYPEDET# indicates
the card would prefer 1.5V. The slots cut in the card edge, encode
whether the card is compatible with 1.5, 3.3V, or both kinds
of motherboards.

So, where does 0.8V come from ? The 0.8V is an _I/O signal level_
rather than an I/O supply voltage. The pad driver is powered by
1.5V. If a series damped termination type is used (AGP 2.0), the
signal level at the end of the bus is 1.5V. That would be suitable
for AGP 4X or slower. To reach the 8X rates, the end of the bus
is parallel terminated inside the chip. The parallel termination
causes a voltage divider action, so the height of the signal seen
on the AGP slot connector measures only 0.8V high.

What this means is, the I/O pads are not powered by 0.8V, they
receive power from 1.5V in both cases.

There is a lot that is unstated, when it comes to the actual
implementation of the silicon. The standard doesn't dictate
how certain things are done, or what combinations of features
are supported. For example, if the parallel terminations at
the end of the bus, can be turned on and off, that would give
the ability for a card to be universal.

http://mirror.ati.com/support/faq/agpchart.html
http://www.ati.com/support/agpchart/agp.html

On the first web page, there are no 0.8V I/O only cards.
They are always 1.5/0.8. There are plenty of older 3.3V only
cards, and those are the ones to avoid.

It would be pretty hard to make a driver that runs from 0.8V
and can drive a parallel termination.

When you buy an 8X card, it generally supports 8X and 4X, as
AGP tries to be backward compatible. 2X is not supported,
as there is no code point in the status register for it.
Why they didn't make the AGP speed field 5 bits wide, I'll
never know.

HTH,
Paul
Click to expand...
Click to expand...
 
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