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Old 05-06-03, 03:05 PM   #3
ricercar
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Join Date: Oct 2002
Location: silicon valley
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There are only two DACs in GeForce4 GPUs. This means only two displays can be driven simultaneously. Thus, a dual-VGA card can drive VGA+VGA or VGA+TV, but never VGA+VGA+TV.

Likewise a DVI+VGA+TV card can drive only two displays at the same time. Because NVIDIA TV output is always on DAC B, the port that shares DAC B with TV cannot be used with TV. Some VGA+DVI+TV cards can do VGA+TV and others can do DVI+TV, but you'll never find a NVIDIA card that can do VGA+TV also capable of DVI+TV.

What I find really bogus is when a VGA + TV card has both TV and VGA on DACB. I have a number of GeForce2 and GeForce4 cards that can't do VGA+TV because both are on DACB and nothing is connected to DACA.

EDIT here's a post I made a while back to help explain nView.
Quote:
Some GeForce2 cards support TwinView and some do not support TwinView, depending on how the OEM manufacturer implements the DACs. All GeForce2 class GPUs have two DACs, DAC A and DAC B. Each DAC can drive one analog display. TwinView requires one display on DAC A and one display on DAC B.

A TV port is supported only on DACB for all NVIDIA GPUs. If an OEM puts an SVideo, RCA, or VIVO connector on a card, it is invariably on DAC B.

A VGA port is supported on both DAC A and DAC B. If the manufacturer provides a VGA port on DAC A, then TwinView is available using <VGA> on DAC A with <TV or VGA> on DAC B.

If the manufacturer puts a VGA port on DAC B and also a TV connector on DAC B, then output is possible for only one display at a time. This is likely how your hardware is manufactured. No driver can make DAC B drive two displays with different images.

One way to verify whether your card has both TV and VGA ports on DAC B is to check it out on the Windows Display control Panel. If the Advanced control panel for your device has "Device Selection" instead of "TwinView " then both ports are using DAC B.
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Last edited by ricercar; 05-06-03 at 03:23 PM.
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