Please read also the important update from November 13!
AGP 4x / 2x and Operational Voltage (continued)
II. Operational Voltage
We come back to Intel's i845 and i850 chipsets and their specifications. Both chipsets are only able to handle AGP 4x or 2x boards with an operational voltage of 1.5V. Especially AGP 2x boards with 1.5V voltage are seldom seen and thus will not often be used in motherboards with these chipsets. Intel's AGP specification explains the operational voltage as follows:
| Signaling Level | AGP 1x Mode | AGP 2x Mode | AGP 4x Mode |
| 3.3 volts | Yes | Yes | No |
| 1.5 volts | Yes | Yes | Yes |
This chart is more than obvious - there is no AGP 4x with a voltage of 3.3 V, but AGP 1x up to AGP 4x is possible with 1.5 volt. The specification contains further corresponding passages showing clearly that an AGP 4x board must have 1.5V default voltage.
Now we have a new but vague clue for differentiation. Some few AGP 2x boards with 1.5V operational voltage may exist, but certainly there should be no AGP 4x boards operating with 3.3 volt.
The Definite Distinguishing Feature of AGP 4x and AGP 2x
The definite distinguishing feature was demonstrated by the mentioned second EPoX press release. A multimeter (if this should not be the correct English term: A multimeter in German means a small and cheap electronic device capable of multiple measurements, e.g. voltage or resistance) may be required but the measuring method is more than simple and once again based on the Intel specifications. A particular pin on the graphic board (and of course inside the AGP slot) delivers the information if there is AGP 4x or 2x respectively 1.5 volt or 3.3 volt. For that we cite the specification:
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"The universal connector will accommodate 3.3 volt signaling for A.G.P. or 1.5 volt signaling for A.G.P. The motherboard or planar will need to detect and supply the correct voltage for the signaling interface based on TYPEDET#. For A.G.P. 3.3 volt signaling add-in cards, TYPEDET# is left open. On an A.G.P. 1.5 volt signaling add-in card, TYPEDET# is hardwired to ground."
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If the specifications are kept, the AGP port will therefore recognise the correct signaling level and provide the appropriate voltage. The hint that the aforementioned "TYPEDET#" pin, which corresponds to the A2 pin of the graphic board according to specification, has to be hardwired to ground in boards with 1.5 volt (mandatory for AGP 4x) and left open in 3.3 volt boards, is very important as it leads directly to the measuring method and the reliable differentiation of 1.5 volt and 3.3 volt boards. This A2 pin is demonstrated by the following photograph:
The photograph shows us the back of the graphic board. The second pin from the right (respectively the slot cover) is the A2 and one can see a strip conductor leading from the A2 pin to a ground dot. Now we can find out with the help of our multimeter, if the pin is connected to ground or not. In principle each multimeter able to measure the electric resistance (ohm) can be used.
The multimeter has to be switched over to ohm and one pole has to be connected to ground (e.g. the graphic board's slot cover), the other pole has to be brought in contact with the A2 pin - all of cause only after removal of the graphic board ;-):
Now matters become thrilling: In case that the A2 pin is hardwired to ground, speaking for an AGP-board with 1.5 volt, the multimeter should display 0.05 ohm. This value may vary depending on the multimeter's measuring tolerances, but the display of something like 0.0x is essential. If instead the multimeter displays "1 .", there is no connection of A2 and ground and it is an 3.3 volt graphic board definitely not to be installed in i845 respectively i850 motherboards.
So we've come to the end of our information article and the measuring of a graphic board's voltage, but we're only at the beginning of the AGP 4x legend.
Please read also the important update from November 13!
