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How to determine the AGP voltage used
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 |
#2
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In article , "Michael S."
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/technolog...0_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 |
#3
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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" wrote in message ... In article , "Michael S." 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/technolog...0_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 |
#4
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In article , "Michael S."
wrote: 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 BTW - Apologies for the AGP doc link. It appears Intel has erased history, by removing their AGP info. This is the first site I could find that still has copies: http://www.ac.uma.es/educacion/curso...I/PCI/agp/?N=A Docs like that don't get backed up on web.archive.org, and I also notice that a number of large companies have had archiving activities stopped, making it easier for them to bury their past. Paul |
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