VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-73
VGA Registers
7HFKQRORJLHV ,QF
:H&
:H&RRQQHFW
QQHFW
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
5Cursor 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
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