Port 3D8  -  Color/VGA Mode control register

                xx1x xxxx  Attribute bit 7. 0=blink, 1=Intesity
                xxx1 xxxx  640x200 mode
                xxxx 1xxx  Enable video signal
                xxxx x1xx  Select B/W mode
                xxxx xx1x  Select graphics
                xxxx xxx1  80x25 text


        The usage of the above control register for various modes is:
                xx10 1100  40x25 alpha B/W
                xx10 1000  40x25 alpha color
                xx10 1101  80x25 alpha B/W
                xx10 1001  80x25 alpha color
                xxx0 1110  320x200 graph B/W
                xxx0 1010  320x200 graph color
                xxx1 1110  640x200 graph B/W