IBM RT Series Hardware Reference Manual page 215

Register 6485 Function
EGA CRTC Function
02H Start Horiz. Retrace Start Horiz. Blanking
03H End Horiz. Retrace End Horiz. Blanking
04H Vertical Total Start Horiz. Retrace
OSH Vertical Total Adjust End Horiz. Retrace
06H Vertical Displayed Vertical Total
07H Vertical Sync Position Overflow
08H Interlace Mode and Skew
Preset Row Scan
Existing applications which utilize the BIOS interface will
generally be compatible with the Enhanced Graphics Adapter.
Horizontal screen centering was required on the IBM
Color / Graphics Monitor Adapter in order to center the screen
when generating composite video. This was done through the
Horizontal Sync Position Register. Since the Enhanced Graphics
Adapter does not support a composite video monitor, programs
which do screen centering may cause loss of the screen image if
centering is attempted.
The Enhanced Graphics Adapter offers a wider variety of
displayable monochrome character attributes than the IBM
Monochrome Display Adapter. Some attribute values may
display differently between the two Adapters. The values listed in
the table below, in any combinations with the blink and intensity
attributes, will display identically.
Background Foreground
R G
B
R G
B
Function
0 0 0 0 0 0
Non-Display
0
0 0
0
0
1 Underline
0 0 0 1 1 1 White Character/Black Background
1
1 1
0 0 0 Reverse Video
Software which explicitly addresses 3D8 (Mode Select Register)
or 3D9 (Color Select Register) on the Color Graphics Monitor
Adapter may produce different results on the Enhanced Graphics
Adapter. For example, blinking which is disabled by writing to
3 D8 on the Color Graphics Adapter will not be disabled on the
Enhanced Graphics Adapter.
IBM Enhanced Graphics Adapter 75