Technical information

CHAPTER 2
Hardware Design
Video System 25
Figure 2-2 Video timing parameters
To accommodate the various VGA and SVGA modes on the Macintosh monitors, the
video controller must have its timing parameters changed by the BIOS. To do that, the
Macintosh software reads the video sense lines and loads the appropriate values for the
video BIOS before starting up the PC. (Remember that system and video BIOS reside in
Macintosh system memory and are modifiable by the software.)
Video
H sync space H image space
H line length
H back porch
H sync pulse
H front porch
HBLANK
/HSYNC
Black
Horizontal timing
Video
V sync space V image space
V line length
V back porch
V sync pulse
V front porch
VBLANK
/VSYNC
Vertical timing
White
Black
White