cos842x@vaxc.cc.monash.edu.au (10/25/89)
This is some information that would save some of you some frustration. Problems: If you have a TRIDENT chip VGA card (8bit), you will find that it will not work properly . It will just work in 800x600 16 colors mode. You would also notice random discolouring vertical band ( I don't know why ?). It would not work in 1024x768 16 colors at all. The ultimate test for different VGA card is AUTOCAD. Solution: I found the problem to be the highest freq oscillator on the card. The TRIDENT VGA uses 40 Mhz. Have notice other brand VGA uses 44.9Mhz I tried 44.9 Mhz, no go. By using a variable oscillator I finally got it to work: Lower freq @ 37 Mhz, high @ 38 Mhz, so required oscillator is 37.5 Mhz. Please note that for 800x600 16 colors an osc of 36-44.9 will work fine. With a 44.9 Mhz 1024x768 in 4 colors works ok. So in summary you need to replace the 40 Mhz by a 37.5 Mhz. Finally, I hope this information will filter back to TRIDENT whom I would have thought would have tested their chip and would have included this info in their spec sheet so that the manufacturer will know what they are doing. I hope I am wrong, I contacted the taiwanese manufacturer, they basically ignored the problem and said it works for them ok in 1024x768 16 colors. I like to see that, it must be the TAIWANESE air or something ! Note: If you are planning to try the experiment yourself, do not be caught by the VGA BIOS sussing out the freq at boot time. The BIOS will interrogate the osc and locks on the highest resolution it can display, so if you change the freq you might have to power off so that the BIOS register the new freq. Good luck. ------------------------------------------------------------------------------- Pan H.Thongvilu. Computer Centre. Monash University, CLAYTON VIC AUSTRALIA 3168.