lauren%lbl-csam@vortex.UUCP (07/31/83)
From: Lauren Weinstein <vortex!lauren@lbl-csam> Greetings. Here in the Vortex, I've had an S100 board around for quite sometime that uses the TI 9918A graphics chip. It's not too bad, but that chip has some, shall we say, "unusual" characteristics. Among these: 1) Sprites (which may be overlayed over any of the graphics modes) are indeed limited to four on any given horizontal line. Any additional sprites will not be displayed until they move off of the "collision" lines. 2) There are some odd "color interactions" depending on which colors are adjacent to other colors in the graphics modes. Some combinations simply don't work (shimmer or are otherwise "damaged") and some combos result in rainbow effects. 3) In video overlay mode (this *does* work IF you have the equipment to set it up right) there is a moving "sawtooth" effect along vertical lines when color video images are being overlayed. This is caused by a pixel mismatch between the timing of chip and the color subcarrier to which the chip is being sync'ed in this mode of operation. I have spoken to some of the people involved in the chip design about these issues, and they are aware of all of them. In most cases, fixes were not possible within the size/cost limitations of the chip, since some limitations are rather fundamental to a single chip design of that type. There are expensive ways around some of the problems, but they're probably not worth the effort. However, having said the above, I must admit that the chip is still pretty darn useful. As long as you avoid color combos that cause problems, it looks pretty nice, and the sprites are rather handy. The basic graphics modes are reasonably flexible, and for most fairly simplistic graphics applications I would rate the chip as acceptable. It's hard to find boards that can perform nearly as well in the same price range. --Lauren--