Path: utzoo!utgpu!watmath!clyde!att!rutgers!deimos!uxc!uxc.cso.uiuc.edu!uxg.cso.uiuc.edu!uxe.cso.uiuc.edu!mcdonald From: mcdonald@uxe.cso.uiuc.edu Newsgroups: comp.sys.ibm.pc Subject: Re: *GA and TC Message-ID: <45900173@uxe.cso.uiuc.edu> Date: 1 Dec 88 14:37:00 GMT References: <422@babbage.acc.virginia.edu> Lines: 16 Nf-ID: #R:babbage.acc.virginia.edu:422:uxe.cso.uiuc.edu:45900173:000:666 Nf-From: uxe.cso.uiuc.edu!mcdonald Dec 1 08:37:00 1988 >VGA is backwards compatible with EGA (i.e. supports EGA modes). However, >I don't think this means that you can hook up an EGA only monitor to a >VGA card (or a VGA monitor to an EGA card) : not referring to the multi- >frequency monitors. VGA is NOT - repeat - NOT - entirely compatible at the programming level with the EGA. It has one important gotcha. There is a bit, the high order bit (128's bit) of the vertical retrace end register, which is at 0x3d5 after 0x11 is sent to 0x3d4, which if set disables writing to a whole bunch of other registers. You have to clear this bit before reprogramming the VGA. Otherwise, it seems to emulate the EGA fine.