User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

110

Figure 25 Display Fields and Dimensions CRxx Control Registers

crt_reg.vsd

Blank (Vertical Back Porch)

Vertical Top Borde

Blank (Vertical Front Porch

Vertical Sync

Vertical Bottom Borde

Horizontal Right Borde

Horizontal Sync

CR12 Vertical Display Enable End

CR15 Vertical Blank Start

CR10 Vertical Sync Start

CR11 Vertical Sync End

CR16 Vertical Blank End

CR06 Vertical Total

CR01 Horizontal Display Enable End

CR02 Horizontal Blank Start

CR04 Horizontal Sync Start

CR05 Horizontal Sync End

CR03 Horizontal Blank End

CR00 Horizontal Total

Display

9.6.1. CRX



CRT Controller Index Register

I/O (and Memory Offset) Address: 3B4h/3D4h

Default: 0Uh (U=Undefined)

Attributes: Read/Write

The value which can be supported at CRX is likely to be impacted by the X09 register which modifies

the meaning of the extended CRxx registers.

Bit Description

7:0 CRT Controller Register Index. These 8 bits are used to select any one of the CRT controller registers

to be accessed via the data port at I/O location 3B5h or 3D5h, depending upon whether the graphics

system is configured for MDA or CGA emulation. The data port memory address offsets are 3B5h/3D5h.