XESS XStend XS40, Manual

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25
sync signal drops low a minimum of 0.94
µ
s after the last pixel and stays low for 3.77
µ
s.
A new line of pixels can begin a minimum of 1.89
µ
s after the horizontal sync pulse ends.
So a single line occupies 25.17
µ
s of a 31.77
µ
s interval. The other 6.6
µ
s of each line is
the horizontal blanking interval during which the screen is dark.
In an analogous fashion, negative pulses on a vertical sync signal mark the start and end
of a frame made up of video lines and ensure that the monitor displays the lines between
the top and bottom edges of the visible monitor screen. The lines are sent to the monitor
within a 15.25 ms window. The vertical sync signal drops low a minimum of 0.45 ms after
the last line and stays low for 64
µ
s. The first line of the next frame can begin a minimum
of 1.02 ms after the vertical sync pulse ends. So a single frame occupies 15.25 ms of a
16.784 ms interval. The other 1.534 ms of the frame interval is the
vertical blanking
interval during which the screen is dark.
•
Figure 8: VGA signal timing.
VGA Signal Generator Algorithm
Now we have to figure out a process that will send pixels to the monitor with the correct
timing and framing. We can store a picture in the RAM of the XS Board. Then we can