ergo@netcom.UUCP (Isaac Rabinovitch) (08/21/90)
In <8960@uhccux.uhcc.Hawaii.Edu> kyung@uhccux.uhcc.Hawaii.Edu (Kyung Lee) writes: >Anyway, is it possible to hookup this VGA card using the same monitor >on a 8 bit XT machine? Is there any software device driver that is >needed if this is possible? And if it is possible, what would be the >maximum res? I know there are 16 bit VGA card that can be used on >8 bit systems. I just don't know if this is one of 'em. Here's some secondhand info. In a recent issue of *Midnight Engineer*, a guy wrote about his experience porting his Macintosh software to MS-DOS, and teaching himself the IBM-compatible culture in the process. His first DOS machine had two monitors: VGA for the application, and MDA for Turbo Debugger. Problem: no underlining, high-intensity, or reverse-video on the monochrome monitor, rendering TD useless. Cause: the high-order byte on the VGA was grabbing every second byte of those meant for the MDA, so all the monochrome attribute bytes were read as 0x00. Solution: move the VGA card to an 8-bit slot. No mention of any special driver needed, though the VGA card may have been one of those "smart" models that configures itself automatically. -- ergo@netcom.uucp Isaac Rabinovitch atina!pyramid!apple!netcom!ergo Silicon Valley, CA uunet!mimsy!ames!claris!netcom!ergo Disclaimer: I am what I am, and that's all what I am!
grege@gold.GVG.TEK.COM (Greg Ebert) (08/22/90)
An AT system will run an 8-bit I/O or memory cycle if -IOCS16 or -MCS16 is not asserted. When you plug a 16-bit card into an 8-bit slot, the video card can't yank the -MCS16 line, so the system 'thinks' it's an 8-bit card. Now the issue is whether or not the card freaks-out. I accidentally plugged an AST VGA card into an 8-bit slot, but it worked just fine. In fact, it's designed to do just that. If you're looking for optimum video performance, you need a system which can 'shadow' the video BIOS into CPU-card-resident RAM. That eliminates wait states during code-fetches from video BIOS. The bottleneck is the AT bus, which must run at 8 Mhz. Even a zero wait-state cycle on the AT bus will result in multiple wait states on, say, a 20 Mhz 386 [not to mention a 33 Mhz 486 :-O ].