Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
WOW Paul--what a nicely-written, detailed answer--THANKS!. I vaguely
remember running some program about a month ago that reported a number of
parameters of the computer and came up with 1.5 volts on the AGP--which is
why I was asking about the 0.8 volts. The general public is told that AGP
4x = 1.5 volts and 8x = 0.8 volts, so I was concerned that my Radeon x800
Pro was being fed too many volts because I overlooked some setting in BIOS
in this computer build, my first since 486's. From your detailed
explanation, I understand WHY the program I was running came up with 1.5
volts on the AGP.
MikeSp
-------------------------------
"Paul" <nospam@needed.com> wrote in message
news:nospam-2107041906120001@192.168.1.177...
> In article <PYSdnSU1A_31QmPdRVn-qQ@comcast.com>, "Michael S."
> <mspurgeon5@comcast.net> wrote:
>
> > As I understand it, an 8X AGP video card operates at 0.8 volts. How can
I
> > determine the voltage being used by the AGP 8X video card by my
P4C800E-D
> > motherboard??
> >
> > I have looked everywhere in the BIOS, in AIDA32 and in Probe data, but
> > either have missed the AGP voltage or just do not know where to look.
> > Aida32 does show an 8X speed. Suggestions?
> >
> > MikeSp
>
> AGP video chips use many voltages, but the voltage in question is
> used to power the I/O pins on the AGP video card and also the
> I/O pins on the Northbridge AGP interface. Matching the capabilities
> of those two chips, so they can share the same voltage, is
> what all this nonsense is about. That is why AGP slots have plastic
> keys, and AGP video cards have slots cut in them, to prevent an
> inappropriate mix of technology.
>
> There are, in fact, only two I/O supply voltages. They are
> 3.3V and 1.5V. The 1.5V is necessary, as modern small geometry
> chips no longer like the 3.3V voltage. They can only handle lower
> voltages. Your P4C800E-D can only handle the lower of the two
> voltages. There is a setting in the BIOS with options like this -
> basically 1.5V, but with room to adjust if needed. Sometimes
> a boost is needed for stability.
>
> "AGP VDDQ Voltage" [1.5, 1.6, 1.7]
>
> So, where does the 0.8V come from ? There are two ways to
> terminate the AGP bus. Termination is any means used to
> suppress signal reflection on an electrical interconnect.
>
> There are two cases. Both electrical cases use VDD = 1.5V for the
> silicon. One case doesn't use a parallel termination resistor
> (it is AGP 4X). The VDDQ fed to the I/O pad results in a full
> ampliude signal and we refer to that as 1.5V I/O.
>
>
> VDD=1.5V Typical AGP 2.0 case VDD=1.5V
> | Full 1.5V signal swing |
> | |
> Driver ------resistance-----the_bus-----+------Receiver
> | |
> | |
> | |
> GND GND
>
>
> In the second case, a parallel termination resistor is used,
> and as near as I can tell, this resistor is actually inside the
> chip. The I/O pads at either end of the bus are still powered
> by 1.5V, but there is a voltage divider action, due to the
> use of the termination at the receiver.
>
> AGP 3.0 case 0.8V swing
> VDD=1.5V Parallel terminator | VDD=1.5V
> | | |
> | v |
> Driver ------resistance-----the_bus-----+------Receiver
> | | |
> | resistance |
> | | |
> GND GND GND
>
> Please note - I haven't build any AGP interfaces, and the
> above figure is my interpretation of what I've been reading.
> Start at PDF page 63 to do your own interpretation.
>
>
http://developer.intel.com/technology/agp/downloads/agp30_final_10.pdf
>
> In conclusion, for an AGP 3.0 card, you cannot measure this
> 0.8V swing, because it only exists on a signal pin, and they change
> too rapidly for any hardware to measure or make sense of them.
> The driver and receiver pads are still powered by 1.5V.
>
> The only thing you would be able to see, is the value of VDD.
> The P4C800E-D doesn't connect the hardware monitor chip to the
> VDD of the AGP. You can set the voltage in the BIOS, but the
> hardware monitoring page in the BIOS doesn't show the result of
> your change. Using a voltmeter on one of the AGP slot pins would
> be one way to verify the voltage.
>
> HTH,
> Paul