Intel 815 Manuel D’Utilisation
Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
R
81
9.1.2. ST01
Input Status 1
I/O (and Memory Offset) Address: 3BAh/3DAh
Default: 00h
Attributes: Read
Default: 00h
Attributes: Read
Only
The address selection is dependent on CGA or MDA emulation mode as selected via the MSR register.
7
6 5
4 3 2
1 0
Reserved
(0)
Reserved
(0)
Video Feedback
Vertical
Retrace
Reserved (00)
Display
Enable
Bit Descriptions
7
Reserved (as per VGA specification). Read as 0s.
6
Reserved. Read as 0.
5:4
Video Feedback 1, 0. These are diagnostic video bits that are selected by the Color Plane Enable
Register. These bits that are programmably connected to 2 of the 8 color bits sent to the palette. Bits 4
and 5 of the Color Plane Enable Register (AR12) selects which two of the 8 possible color bits become
connected to these 2 bits of this register. The current software normally does not use these 2 bits. They
exist for EGA compatibility.
Register. These bits that are programmably connected to 2 of the 8 color bits sent to the palette. Bits 4
and 5 of the Color Plane Enable Register (AR12) selects which two of the 8 possible color bits become
connected to these 2 bits of this register. The current software normally does not use these 2 bits. They
exist for EGA compatibility.
3
Vertical Retrace/Video.
0 = VSYNC inactive (Indicates that a vertical retrace interval is not taking place).
1 = VSYNC active (Indicates that a vertical retrace interval is taking place).
Note:
Bits 4 and 5 of the Vertical Retrace End Register (CR11) can program this bit to generate an interrupt at
the start of the vertical retrace interval. This ability to generate interrupts at the start of the vertical retrace
interval is a feature that is largely unused by current software.
Bits 4 and 5 of the Vertical Retrace End Register (CR11) can program this bit to generate an interrupt at
the start of the vertical retrace interval. This ability to generate interrupts at the start of the vertical retrace
interval is a feature that is largely unused by current software.
2:1
Reserved. Read as 0s.
0
Display Enable Output.
0 = DE inactive. Active display area data is being drawn on the display. Neither a horizontal retrace
interval or a vertical retrace interval is currently taking place.
1 = DE active. Either a horizontal retrace interval or a vertical retrace interval is currently taking place.