Intel 815 Manuel D’Utilisation
Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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Bit Description
0
Vertical Total Bit 8. The vertical total is a 10-bit or 12-bit value that specifies the total number of scan
lines. This includes the scan lines both inside and outside of the active display area.
lines. This includes the scan lines both inside and outside of the active display area.
In standard VGA modes, where bit 0 of the I/O Control Register (CR80) is set to 0, the vertical total is
specified with a 10-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the
Vertical Total Register (CR06), and the most and second-most significant bits are supplied by bit 5 and
this bit, respectively, of this register.
specified with a 10-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the
Vertical Total Register (CR06), and the most and second-most significant bits are supplied by bit 5 and
this bit, respectively, of this register.
In extended modes, where bit 0 of the I/O Control Register (CR80) is set to 1, the vertical total is
specified with a 12-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the
Vertical Total Register (CR06), and the 4 most significant bits are supplied by 3-0 bits of the Extended
Vertical Total Register (CR30). In extended modes, neither this bit, nor bit 5 of this register are used.
specified with a 12-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the
Vertical Total Register (CR06), and the 4 most significant bits are supplied by 3-0 bits of the Extended
Vertical Total Register (CR30). In extended modes, neither this bit, nor bit 5 of this register are used.
This 10-bit or 12-bit value should be programmed to be equal to the total number of scan lines, minus 2.
9.6.10. CR08
Preset Row Scan Register
I/O (and Memory Offset) Address: 3B5h/3D5h (index=08h)
Default:
Default:
0UUU UUUUb (U=Undefined)
Attributes: Read/Write
7 6
5
4
0
Reserved
(0)
Byte Panning
Starting Row Scan Count
Bit Description
7
Reserved. Read as 0s.
6:5
Byte Panning. This field holds a 2-bit value that selects number of bytes (up to 3) by which the image is
shifted horizontally to the left on the screen. This function is available in both text and graphics modes.
shifted horizontally to the left on the screen. This function is available in both text and graphics modes.
In text modes with a 9-pixel wide character box, the image can be shifted up to 27 pixels to the left, in
increments of 9 pixels. In text modes with an 8-pixel wide character box, and in all standard VGA
graphics modes, the image can be shifted up to 24 pixels to the left, in increments of 8 pixels.
increments of 9 pixels. In text modes with an 8-pixel wide character box, and in all standard VGA
graphics modes, the image can be shifted up to 24 pixels to the left, in increments of 8 pixels.
The image can be shifted still further, in increments of individual pixels, through the use of bits [3:0] of
the Horizontal Pixel Panning Register (AR13).
the Horizontal Pixel Panning Register (AR13).
Number of Pixels Shifted
Bit [6:5]
9-Pixel Text
8-Pixel Text & Graphics
00 0
0
01 9
8
10 18
16
11 27
24
4:0
Starting Row Scan Count. This field specifies which horizontal line of pixels within the character boxes
of the characters used on the top-most row of text on the display will be used as the top-most scan line.
The horizontal lines of pixels of a character box are numbered from top to bottom, with the top-most line
of pixels being number 0. If a horizontal line of the these character boxes other than the top-most line is
specified, then the horizontal lines of the character box above the specified line of the character box will
not be displayed as part of the top-most row of text characters on the display. Normally, the value
specified by these 5 bits should be 0, so that all of the horizontal lines of pixels within these character
boxes will be displayed in the top-most row of text, ensuring that the characters in the top-most row of
text do not look as though they have been cut off at the top.
of the characters used on the top-most row of text on the display will be used as the top-most scan line.
The horizontal lines of pixels of a character box are numbered from top to bottom, with the top-most line
of pixels being number 0. If a horizontal line of the these character boxes other than the top-most line is
specified, then the horizontal lines of the character box above the specified line of the character box will
not be displayed as part of the top-most row of text characters on the display. Normally, the value
specified by these 5 bits should be 0, so that all of the horizontal lines of pixels within these character
boxes will be displayed in the top-most row of text, ensuring that the characters in the top-most row of
text do not look as though they have been cut off at the top.