6600sirt@ucsbuxa.ucsb.edu (Mike O'Brien) (02/14/91)
Ok, here's the challenge: try to pan a 320x200x256 graphics screen
one pixel to the left. Sounds easy? Well check this out...
[1] The CRTC Start Address registers don't correspond to the screen's
real start address. If you set the start address to 0100h, for
example, then the real start address will be 0A000h:0400h! In
other words, it multiplies whatever you give it by four. Why??
[2] If you try to change the Horizontal Pixel Pan register, the
adapter will actually take itself out of 320x200x256 mode! It
seems to set itself to 640x200x16.
So the best I can do is to scroll the screen four pixels at a time.
Is this a serious design oversight with the MCGA, or a serious
oversight on my part?
Mike
6600sirt@ucsbuxa.ucsb.edu