Chapter 5
Configuration Utility
PCI/PXI-1408 and NI-IMAQ for Win95/NT
5-10
©
National Instruments Corporation
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CLAMP Start and CLAMP Stop—The clamp signal restores the
DC level of the AC-coupled video signal. CLAMP Start and
CLAMP Stop are specific to the current StillColor mode.
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Monochrome (StillColor disabled) or StillColor RGB mode—
The clamping pulse must be positive (CLAMP Stop >
CLAMP Start) and must be applied on each line somewhere
during the blanking period of the video signal. For a color
camera, this typically occurs between the end of the color burst
and the beginning of the active video line. For a monochrome
camera, this typically occurs anytime on the back porch period
of the video signal.
The duration of the pulse (CLAMP Stop – CLAMP Start)
should be as long as possible and greater than five samples. As
shown in Figure 5-4, position A corresponds to the position of
CLAMP Start for a monochrome camera and position B
corresponds to the position of CLAMP Start for a
monochrome acquisition from a color composite camera.
Position C corresponds to CLAMP Stop for either a
monochrome or color camera.
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StillColor Composite mode—The clamping pulse must be
positive (CLAMP Stop > CLAMP Start) and must be applied
on each line somewhere during the horizontal synchronization
pulse of the video signal. The duration of the pulse
(CLAMP Stop – CLAMP Start) should be as long as possible
and greater than five samples. Figure 5-5 illustrates the correct
position of CLAMP Start and CLAMP Stop.
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ZERO Start and ZERO Stop—The zero signal calibrates the ADC
on each video line. The pulse conditions—positioning and
duration—are the same as for the clamping pulse. ZERO Start and
ZERO Stop are also specific to the current StillColor mode.
Positioning information is the same as CLAMP Start and
CLAMP Stop.
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NGate Start and NGate Stop—The noise gate (NGate) settings
define the period of a video line after lock to a video source where
the genlock circuitry will not detect a HSYNC pulse. The 1408
device uses this nondetection period to avoid false HSYNC
detection due to noise in the video signal or equalization pulses
during the vertical synchronization period. For a typical video
signal, the NGate signal starts after HSYNC Stop and stops
approximately 3% before the end of the video line defined by
HCOUNT. Figure 5-4 illustrates the correct position of
NGATE Start and NGATE Stop.
