VGA video timings
Kenneth Kramer
Posts: 11
Hi friends,
I'm planning to make a simple video generator (for a start, until I know the basic technics to make something more advanced). A 640x480 resolution mode has the following video timings:
Vertical timings:
Refresh rate = 60 Hz
Vsync = 0.06 ms/2 lines
Front porch = 1.02 ms/32 lines
Vactive = 15.25 ms/480 lines
Blanking = 0.35 ms/11 lines
Horizontal timings:
Scan rate = 31476 Hz
Hsync = 3.77 us/96 dots
Front porch = 1.89 us/48 dots
Hactive = 25.17 us/640 dots
Back porch = 0.94 us/24 dots
What confuses me is how the horizontal and vertical timings interact with each other. This is how I see it:
1) When the last visible horizontal scan line has ended, the vsync pin must be pulled low.
This marks the start of the vertical blanking interval (front porch = 1.02 ms). During this period, 32 horizontal scan lines completes the front porch interval.
2) When the front porch interval has ended, the hsync pin remains low and the beam is moved from the lower right to the upper left corner (blanking = 0.35 ms).
3) While the vsync pin is still low, 2 additional horizontal scan lines mark the start of 480 visible scan lines.
After the completion of these 2 scan lines, vsync is pulled high to end the vertical blanking interval.
Each scan line ends when pulling the hsync pin low for [noparse][[/noparse]back porch + hsync + front porch = 6.6 us].
The dots and lines are calculated from formulas derived from the video timing information.
Thanks,
Kenneth
I'm planning to make a simple video generator (for a start, until I know the basic technics to make something more advanced). A 640x480 resolution mode has the following video timings:
Vertical timings:
Refresh rate = 60 Hz
Vsync = 0.06 ms/2 lines
Front porch = 1.02 ms/32 lines
Vactive = 15.25 ms/480 lines
Blanking = 0.35 ms/11 lines
Horizontal timings:
Scan rate = 31476 Hz
Hsync = 3.77 us/96 dots
Front porch = 1.89 us/48 dots
Hactive = 25.17 us/640 dots
Back porch = 0.94 us/24 dots
What confuses me is how the horizontal and vertical timings interact with each other. This is how I see it:
1) When the last visible horizontal scan line has ended, the vsync pin must be pulled low.
This marks the start of the vertical blanking interval (front porch = 1.02 ms). During this period, 32 horizontal scan lines completes the front porch interval.
2) When the front porch interval has ended, the hsync pin remains low and the beam is moved from the lower right to the upper left corner (blanking = 0.35 ms).
3) While the vsync pin is still low, 2 additional horizontal scan lines mark the start of 480 visible scan lines.
After the completion of these 2 scan lines, vsync is pulled high to end the vertical blanking interval.
Each scan line ends when pulling the hsync pin low for [noparse][[/noparse]back porch + hsync + front porch = 6.6 us].
The dots and lines are calculated from formulas derived from the video timing information.
Thanks,
Kenneth