Knox Video VS-200 - Manual (Page 46)

K NOX V IDEO VS-200 O PERATION M ANUAL
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A video frame includes both the active area, the portion of the image normally
containing useful visual information, and a resolution value for a given display
standard which only expresses the number of pixels visible in an image.
The well-known 800 x 600 computer resolution standard simply means that there are
800 pixels/line visible horizontally and there are 600 lines visible vertically.
This item provides a way to change the number of active pixels and lines.
There is a period of time between the end of the Horizontal Sync pulse and the start
of Active Video. This portion of the waveform signal is called the “Back Porch”, a
term originating with the television broadcasting industry and its RS-170A
specification. In practice, this will control where the video image starts on the left
side of the monitor without changing the width of the sync pulse itself (another way to
control where the image area starts). The two parameters control where the back
porch is positioned and they interact to a degree.
By adjusting these parameters, you control the start of the back
porch (with respect to the trailing edge of Horizontal Sync) and
also its width. The place where the Back Porch begins with
respect to the Horizontal Sync pulse and the width of the Back
Porch have a direct bearing on where the active (visible) portion of the image begins.
Do not attempt this adjustment without monitoring the results with an oscilloscope.
There are standards for all current computer and broadcast resolutions that specify
the correct width of both Vertical and Horizontal synchronizing pulses.
If you are creating a special, non-standard resolution, you may wish to adjust the
pulse width to fit your new requirements. The H/V Sync screen is where that is
accomplished.
Like the H/V Start adjustment, you must use an oscilloscope when
making these adjustments so that you know exactly how many
milliseconds or microseconds of pulse width you have created.
The numbers shown are relative numbers and not an actual time
measurement.
800 x 600 60 Hz
H/V active [ 800] x 600
800 x 600 60 Hz
H/V Start [ 88] x 23
800 x 600 60 Hz
H/V Sync [ 128] x 4