[OFF TOPIC?] Fixed Freq Monitor Questions

OK, This is mildly on topic. My monitor is an HP 1097C, making it at least 10 years old. However, I am using it with a modern PC, so that's where the 'on topic' issue gets a little iffy. I'm sure there are plenty of people here who can answer this question. A pointer to a FAQ would be most welcome. These old monitors are Fixed frequency, unlike our modern monitors which multisync. The 1097C supports only a 78.125 khz Horizontal Scan Rate and a 72hz Vertical Refresh Rate. Now a couple of years ago I foolishly bought one of those cards by Mirage (www.mirage-mmc.com) which is supposed to be a 'fixed freq video card'. Actually, it's an OEM Diamond card, basically an S3/968 video processor with an IBM 52x RAMDAC - ala Diamond Stealth VRAM. The fixed Freq hacks are basically a resistor (and a jumper selection) to drive sync over green, and a homebrew PROM to skew the VESA frequencies for several video and text modes. It works, but Mirage hasn't been too helpful with getting a variety of XFree86 modelines, even though they claim to support Linux and XFree86. They give out _one_ modeline for 1280 x 1024, which they swiped from the XFree86 distribution in 'Monitors.txt'. For Windows and Dos, they give out a video driver which seems to work just fine. It will even display 320x200 full screen (Quake works great in DOS!), and boots to a functional 80x24 col text mode. How the hell do they do this? Here is how I'm calculating my video modes based in the XFree86VideoModes HOWTO (found in every Redhat 5 distribution): Dot Clock Per Second Total Horizontal Pixels Per Line = -------------------------- Horizontal Scanning Rate Since my refresh rate must be at 72hz to sync with the HP1097C: Dot Clock Refresh Rate = ------------------------------------------------- Horizontal Frame Length * Vertical Frame Length So, it's really more constructive to think of this as how many pixels _total_ do I need to display in order to get a 72 hz vertical scan rate with any arbitrary dot clock? In this case I need Dot Clock Total Pixels Per Frame (HFLxVFL) = ------------- Refresh Rate Since I know my Horizontal Pixels Per Line, I can use this to determine the number of vertical lines which will support a 72 hz refresh rate.... hmmm, this is where things get sticky. We'll start with a DCL of 10Mhz... 10Mhz Dot Clock 128 Horizontal Pixels = ----------------------------- 78125 hz Vertical Scan Rate 10 Mhz Dot Clock 138888 Total Pixels = --------------------------- 72 hz Refresh Rate 138888.88 Pixels 1085 Vertical Lines Per Frame = ----------------------- 128 Horizontal Pixels Sheesh! A (total) screen resolution of 128H x 1085V? What about a 20 Mhz dot clock? Well, after graphing the results I quickly observed this: S | T C | o R R | 128H 256H 384H 512H 640H 1728H ** T E E | x x x x x x A E S | 1085V 1085V 1085V 1085V 1085V 1085V L N | | DCL ----+------+-------+-------+-------+------- [...] ----+----- 10 20 30 40 50 135 (** Perfect for a usful screen resolution of 1280x1024) So, based on this, I cannot get small or talored screen resolutions unless I am willing to accept wide borders and strange resolutions. Yet my card works....It does _not_ display this behavior... so I suspect my thinking is to blame. Will someone please correct me? Apologies if you consider this post off topic... J. Maynard Gelinas