Product specifications

VT8601A Apollo PLE133
Revision 1.82 October 22, 2001 -72- VGA Registers
Technologies, Inc.
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VGA CRT Controller Registers (CR)
CRTC registers are accessible at either 3B4 / 3B5 or 3D4 /
3D5 (shorthand notation 3x4 / 3x5) depending on the setting
of Miscellaneous Output Register 3C2 bit-0
Port 3x4 – VGA CRT Controller Index...........................RW
7-0 CRT Controller Index
Only the lower 5 bits are implemented in a standard
VGA to allow access to CRTC registers 0-18h.
However, all 8 bits are implemented here to allow for
extended registers up to index FF.
Port 3x5 Index 0 – VGA CRTC – H Total.......................RW
7-0 Horizontal Total........................................default = 0
Port 3x5 Index 1 – VGA CRTC – H Display Ena End...RW
7-0 Horizontal Display Enable End...............default = 0
Port 3x5 Index 2 – VGA CRTC – H Blank Start............RW
7-0 Horizontal Blanking Start........................default = 0
Port 3x5 Index 3 – VGA CRTC – H Blank End..............RW
7 Reserved .........................................always reads 0
6-5 Display Enable Skew ................................default = 0
4-0 Horizontal Blanking End .........................default = 0
Port 3x5 Index 4 – VGA CRTC – H Retrace Start.........RW
7-0 Horizontal Retrace Pulse Start......... default = 0FFh
Port 3x5 Index 5 – VGA CRTC – H Retrace End ..........RW
7 Horizontal Blanking End .........................default = 0
6-5 Horizontal Retrace Delay.........................default = 0
4-0 Horizontal Retrace Pulse End .................default = 0
Port 3x5 Index 6 – VGA CRTC – V Total.......................RW
7-0 Vertical Total ............................................default = 0
Port 3x5 Index 7 – VGA CRTC – Overflow....................RW
7 Vertical Retrace Start Bit-9.....................default = 0
6 Vertical Display Enable End Bit-9..........default = 0
5 Vertical Total Bit-9 ...................................default = 0
4 Line Compare Bit-8 ..................................default = 0
3 Vertical Blank Start Bit-8 ........................default = 0
2 Vertical Retrace Start Bit-8 ....................default = 0
1 Vertical Display Enable End Bit-8..........default = 0
0 Vertical Total Bit-8 ...................................default = 0
Port 3x5 Index 8 – VGA CRTC – Preset Row Scan .......RW
7 Reserved .........................................always reads 0
6-5 Byte Panning .............................................default = 0
4-0 Preset Row Scan........................................default = 0
Port 3x5 Index 9 – VGA CRTC – Max Scan Line ..........RW
7 200 to 400 Line Conversion......................default = 0
6 Line Compare Bit-9 ..................................default = 0
5 Vertical Blank Start Bit-9 ........................default = 0
4-0 Maximum Scan Line.................................default = 0
Port 3x5 Index A – VGA CRTC – Cursor Start.............RW
7-6 Reserved .........................................always reads 0
5 Cursor On/Off........................................... default = 0
4-0 Cursor Row Scan Start ............................ default = 0
Port 3x5 Index B – VGA CRTC – Cursor End...............RW
7 Reserved .........................................always reads 0
6-5 Cursor Skew.............................................. default = 0
4-0 Cursor Row Scan End.............................. default = 0
Port 3x5 Index C / D – VGA CRTC Start Addr Hi/Lo..RW
............................................... default = 0
Port 3x5 Index E / F – VGA CRTC Cursor Loc Hi/Lo..RW
............................................... default = 0
Port 3x5 Index 10 – VGA CRTC – V Retrace Start.......RW
7-0 Vertical Retrace Pulse Start .................... default = 0
Port 3x5 Index 11 – VGA CRTC – V Retrace End ........RW
7 CR0-7 Write Protect................................. default = 0
6 Reserved .........................................always reads 0
5 Vertical Interrupt Enable ........................ default = 0
4 Vertical Interrupt Clear........................... default = 0
3-0 Vertical Retrace Pulse End...................... default = 0
Port 3x5 Index 12 – VGA CRTC – V Display Ena End.RW
7-0 Vertical Display Enable End ................... default = 0
Port 3x5 Index 13 – VGA CRTC – Offset .......................RW
7-0 Display Screen Logical Line Width ........ default = 0
Port 3x5 Index 14 – VGA CRTC – Underline Location RW
7 Reserved .........................................always reads 0
6 Double Word Mode.................................. default = 0
5 Count By 4 .............................................. default = 0
4-0 Underline Location................................... default = 0
Port 3x5 Index 15 – VGA CRTC – V Blank Start..........RW
7-0 Vertical Blanking Start............................ default = 0
Port 3x5 Index 16 – VGA CRTC – V Blank End............RW
7-0 Vertical Blanking End.............................. default = 0
Port 3x5 Index 17 – VGA CRTC – Mode Control..........RW
7 Hardware Rese.......................................... default = 0
6 Word / Byte Mode..................................... default = 0
5 Address Wrap ........................................... default = 0
4 VSYNC Update Select (VGA Extended Capability)
0 Base may only
be updated during Vsync .....def
1 Base address may be updated during Hsync
3 Count By 2 ............................................... default = 0
2 Horizzontal Retrace Select....................... default = 0
1 Select Row Scan Counter......................... default = 0
0 Compatibility Mode Support .................. default = 0
Port 3x5 Index 18 – VGA CRTC – Line Compare.........RW
7-0 Line Compare ........................................... default = 0