Rage3D really broke the news on the possible limitations of the Silicon Image Sil 1161 receiver that ATI's CrossFire utilized. The receiver can handle a max of 1600x1200 at 60 Hz (or essentially receive 60 1600x1200 frames per second), and runs at a maximum of 165 MHz. At first this limitation looks like a huge disaster waiting to happen to ATI with the release of CrossFire, and many are screaming that the engineers fell down on the job and should all be sacked. When I was first given this information, I originally thought that ATI had made a big blunder... but upon further investigation I believe that it really isn't that big of a limitation at all.
The DVI spec is actually pretty flexible, and by doing tricks such as blanking, higher resolutions can be achieved that should be normally out of the range of the chips involved. Since Silicon Image actually developed the spec, they definitely know it inside and out. The first thing we need to do is separate the fact from fiction, and really show what is going on as well as the limitations that really are there. What we should remember, first and foremost, is that we don't know the exact engineering processes and tricks that ATI is using for their CrossFire implementation. ATI has some pretty clever engineers, and I don't think that something this obvious got past them.
First off the Sil 1161 receiver simply receives the pixel data from the slave board. That data is sent to the compositing engine, which then takes the final frame/s and sends it to either its built in TMDS transmitter or the RAMDAC, both of which can handle 2048x1536 @ 85 Hz. The Sil 1161 has NOTHING to do with the refresh rate of the screen that is connected to the master card. So, at the very least, CrossFire users can enjoy refresh rates on CRT monitors greater than 60 Hz at resolutions above 1600x1200 because that is based on the transmitters on the master card, which are essentially identical to every other standalone, high-end ATI card.
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PenStar Systems
Sep 17, 2005, 07:24 AM
