User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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9.6.2. CR00

Horizontal Total Register
I/O (and Memory Offset) Address: 3B5h/3D5h (index=00h)
Default: 00h
Attributes: Read/Write (Group 0 Protection)
This register is used to specify the total length of each scan line. This encompasses both the part of the
scan line that is within the active display area and the part that is outside of it. This register is extended to
cover 16x12 resolution using CR35 and CR39.
Bit Description
7:0 Horizontal Total. This field should be programmed with a value equal to the total number of character
clocks within the entire length of a scan line, minus 5.
9.6.3. CR01

Horizontal Display Enable End Register
I/O (and Memory Offset) Address: 3B5h/3D5h (index=01h)
Default: Undefined
Attributes: Read/Write (Group 0 Protection)
This register is used to specify the end of the part of the scan line that is within the active display area
relative to its beginning. In other words, this is the horizontal width of the active display area.
Bit Description
7:0 Horizontal Display Enable End. This field should be programmed with a value equal to the number of
character clocks that occur within the part of a scan line that is within the active display area, minus 1.
9.6.4. CR02

Horizontal Blanking Start Register
I/O (and Memory Offset) Address: 3B5h/3D5h (index=02h)
Default: Undefined
Attributes: Read/Write (Group 0 Protection)
This register is used to specify the beginning of the horizontal blanking period relative to the beginning
of the active display area of a scan line.
Bit Description
7:0 Horizontal Blanking Start. This field should be programmed with a value equal to the number of
character clocks that occur on a scan line from the beginning of the active display area to the beginning
of the horizontal blanking.