We mentioned three CrossFire modes above, but there is a fourth one. The Super AA mode differs from the other three in improving the image quality rather than increasing the performance. A CrossFire system makes 8x, 10x, 12x and 14x full-screen antialiasing modes available.
The 8x and 12x modes are improved versions of the 4x and 6x modes, respectively. In this case each graphics card works in FSAA 4x or 6x mode, but the samples at multi-sampling are taken from different locations. The quality of the subsequent merger of the two resulting frames is equivalent to MSAA 8x/12x. The 10x and 14x modes are hybrid ones, combining 2x super-sampling with 4x/6x multi-sampling for a near ideal quality of small image details and smoothing out transparent textures. The number of texture samples is doubled in the Super AA mode, so the anisotropic filtering range is doubled, too. In other words, AF 32x mode becomes available. Super AA is unavailable if you use one of the three performance-boosting rendering modes, but you can use the ordinary 2x/4x/6x FSAA with them.
As mentioned above, the information from the Slave card is transferred to the Master via an external Y-shaped cable in the DVI format. This is a snapshot of the cable:
The multi-pin DMS-59 connector is attached to a special connector on the PCB of the Master card, the male DVI connector – to the DVI connector of the Slave card and the female DVI-I connector to the DVI output of your TFT monitor or, via an ordinary DVI-I → D-Sub adapter, to any CRT monitor.
To implement different rendering methods in one graphics subsystem ATI had to use a programmable FPGA matrix, capable of changing its structure depending on the task at hand, as a chip that combines the parts of the image. The employed Xilinx XC3S400 chip belongs to the Spartan-3 series, consists of 400 thousand transistors, and has 8064 logical cells and 43 kilobytes of integrated memory.
To translate the resulting information into a FPGA-matrix-friendly form, a 165MHz TFP401A chip from Texas Instruments is used. The frame can be outputted to an analog monitor through an ADV7123 chip (a three-channel 10-bit 330MHz RAMDAC) or to a DVI-interfaced LCD panel through an ordinary TMDS transmitter SiI1162.
The single-link receiver from TI is actually a weak link since its operational frequency is only 165MHz, so the maximum supported resolution is UXGA (1600x1200). The use of this receiver is necessary because the Slave card has a 165MHz transmitter with the same limitation. This doesn’t seem to be a big problem as a majority of monitors in use simply do not support higher resolutions, but there’s an unpleasant surprise for any CrossFire user.