PCVisionplus
Hardware Reference
Theory of Operation
2–37
Rev 02; February 8, 2002
RGB Video
VBLANK
Vsync
HBLANK
Trigger Input
TRGCYC0
FIFO Load
TRGEN0
STROBE
STRBDLY
Figure 2–35. Triggered Acquire Cycle in Slow Strobe
2.7.7.6 Trigger on Frame-Fast Strobe Mode
Fast strobe mode outputs a strobe pulse immediately after an external trigger input, unless the trigger occurs in the
“no-strobe region”. The no-strobe region is a number of lines from Vsync, programmed in the STRBDLY register.
After the external trigger input, the next field or frame is loaded into the image memory and acquired by the frame
memory. If the external trigger occurs coincident with VSYNC, the strobe is delayed past the no-strobe region and
the acquire is delayed to the next field. The strobe pulse is one line in duration, and polarity is programmable.
In Figure 2–36, the trigger cycle begins on the next vertical blank after the external trigger pulse.
The strobe pulse
occurs immediately, or the strobe delay counter starts. If the trigger occurs in the no-strobe region, the strobe pulse
will not occur until the end of the no-strobe region, at the end of the STRBDLY count. At the first Vsync pulse after
the trigger, TRIGEN is cleared and TRIGCYC set high, indicating the triggered acquire cycle has begun. One or two
fields are acquired and loaded into the image memory based on the PWG programming.
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