The Measuring Method and its Drawback
We had described by means of a multimeter how to determine if the A2 pin (or TYPEDET# according to Intel's AGP2.0 specification) is hardwired to ground or not.
We didn't reinvent the wheel since this determination method was provided by a press release of the motherboard manufacturer EPoX, as described in our previous article. Our investigations, especially the lecture of the AGP2.0 specification, led repeatedly to the description of the A2 pin, so we like to cite the specification itself:
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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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The wording of this passage already refutes the reliability of our measuring method, because we didn't pay attention to the fact that it exclusively refers to the AGP universal slot!
The direct hint came from Hercules' engineering department:
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"Regarding
Pin A2 signal, this pin signal is read only on AGP universalbus
(with no AGP 4X notch), and on AGP universal bus, our board switch to AGP
signals in 3.3 volts, you can read this spec on AGP 2.0 specs (chapters
4.3.5 and 4.3.6), so this Pin A2 signal is not relevant for a test on a non
universal AGP bus, as on DFI VC11, and as on other i845 motherboards.
The only conclusion
one can make from Pin A2 signal is that, on a AGP
universal bus (without the 4X notch), you use a 3.3 volts, but that is a signal
voltage only for an AGP universal bus, it is not the signal for a i845 or
i850 AGP bus."
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The renewed inspection of the AGP2.0 specifications confirmed that the AGP universal slot is the only AGP slot reading the A2 pin for distinguishing between 3.3V and 1.5V graphic boards and therefore recognizing a graphic board to comply with AGP4x or not.
Conclusions and Further Examinations
The question, why the A2 pin isn't basically connected to ground, what would be logical after all when considering that the vast majority of motherboards provides AGP universal slots, remains unsettled. In consequence a graphic board capable of AGP4x, providing a signaling level of 1.5V but an unconnected A2 pin will only be recognized and operated in AGP2x mode when plugged into a motherboard with AGP universal slot.
Additionally we have discussed this issue with Mr. Christian Reul, graduated engineer and Brand Manager of Hercules Germany. With regard to the unconnected A2 pin of Hercules' Kyro II graphic boards (3D Prophet 4500), Mr. Reul stated that these boards are intended for the broad entry-market and that leaving the A2 pin unconnected was assumed to provide the highest possible compatibility when updating older computer systems.
Considering our Hercules 3D Prophet II GTS Pro, whose A2 pin isn't connected as well and which therefore was recognized merely as AGP2x graphic board by our testing motherboards, it was explained that due to stability issues these boards were initially advertised as AGP1x/2x boards only, even disabling AGP4x by firmware. This particular board is still tested in Hercules' engineering department in France, so there is no feedback as yet. Interestingly it was assured that the newer boards of this series, in both the long and short design, are available with connected A2 pin as well. But that's just another business.
Final Words
Our today's article pointed out that our original approach for solving the problem fails to work. The method using the multimeter is only able to discover the following:
- If the A2 pin (TYPEDET#) is hardwired to ground, the corresponding graphic board is definitely providing a signaling level of 1.5V.
- If the A2 pin (TYPEDET#) is not hardwired to ground, the graphic board's signaling level may be 1.5V, but merely 3.3V as well.
Thus there's no simple method for determining whether a graphic board is suitable for operating in i845/i850 and nForce motherboards or not. We solely can cite the following list of graphic boards definitely not capable of 1.5V according to the graphic board manufacturer PowerColor:
- all nVidia Vanta, Vanta LT
- all SiS 6326
- all S3 Savage4 below revision 3.0
- all 3dfx graphic boards (officially non-AGP4x anyhow)
In case of intending to operate an AGP2x graphic board in i845/i850 or nForce motherboards, the graphic board manufacturer should be consulted for safety reasons.
Peter, November 24th, 2001
translated by Volkmar, December 13th, 2001
