MV1000 Application Notes

MV-1000/MV-1500 Capture Control using External Trigger

Overview

M-Vision-1000
This Application Note describes the behavior for both the MV-1000 and MV-1500 boards using the GRAB_TRIG control to initiate image capture. This shall not be confused with another feature, C_SIG_TRIG , provided by the MV-1500 board and MV-1100 module, for counter register trigger control.

This Application Note will use signal waveforms to help readers to understand the discussion. To simplify the discussion, all examples and drawings in this Application Note refer to non-interlaced video signals.

All the following discussions assume that the MV-1000 or MV-1500 uses active low for the trigger polarity and will start to capture at the 20th line. It is also assumed that the board has been programmed to use GRAB_TRIG for capture control; this can be done either through the field External_Trigger in the camera configuration file, or by the function call MV1SetExtTriggerMode() in the program.

Technique Outline

Level Trigger vs. Edge Trigger

The GRAB_TRIG signal for image capture on both the MV-1000 and MV-1500 is LEVEL triggered, not EDGE triggered.



In the above drawing, if the GRAB_TRIG signal is already LOW before a call to MV1StartGrab(), the next available frame will be captured, even though there is no "edge" of the GRAB_TRIG signal after the function call.

The Width of the Trigger Pulse

The width of the trigger pulse is irrelevant. Based on our testing results, a pulse of 3 µs in width will trigger the capture. We did not try any narrower pulse.

The Timing of the Trigger Presence

The trigger signal has to be present one line before the capture starting line number. For the definition of "starting line number", please refer to The Camera Configuration File Format in the User's Guide or the Software Development Guide. In this example, we set the board to capture a single frame starting at 20th line, the trigger signal shall therefore be no later than 19th line. Otherwise, the capture will start at the next frame.



The Width of Trigger Signal in Continuous Grab

If the trigger signal resets prior to the completion of current frame capture controlled by the ending line number, the board will stop capturing until the trigger signal is present again. For the definition of "ending line number", please refer to The Camera Configuration File Format in the User's Guide or the Software Development Guide



If the trigger signal resets prior to the completion of current fraIf the trigger signal resets after the last line of current frame is captured, the next frame will be captured. This is shown in the next drawing.





MuTech Corp. Sept 1996
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