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CRTC Overflow Register Format
Bit
7
6
5
4
3
2
1
0
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Vertical Total Bit 8
Vertical Display Enable End Bit 8
Vertical Retrace Start Bit 8
Start Vertical Blank Bit 8
Line Compare Bit 8 '
L...-_ _ _ _ _
~-'"~
Cursor Location Bit 8
Not Used
Vertical Total-Bit 8 of the Vertical Total
register (index hex 06).
Vertical Display Enable End-Bit 8 of the
Vertical Display Enable End register (index hex
12).
Vertical Retrace Start-Bit 8 of the Vertical
Retrace Start register (index hex 10).
Start Vertical Blank-Bit 8 of the Start Vertical
Blank register (index hex 15).
Line Compare-Bit 8 of the Line Compare
register (index hex 18).
Cursor Location-Bit 8 of the Cursor Location
register (index hex OA).
Preset Row Scan Register
This is a write-only register pointed to when the value in the CRT
Controller address register is hex 08. The processor output port
address for this register is hex 3B5 or hex 3D5.
IBM Enhanced Graphics Adapter 31
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