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External Trigger
An external trigger can be used to start video capture precisely at the right time. Connect
the external trigger to the Sync IN input (See Fig. 9). The trigger should provide a 3.3V
logical levels. Video capture can be started by either rising or falling edge.
The input is internally pulled up (10k resistor) to 3.3V. It enables triggering the video
capture manually with a push button that simply grounds the input.
External trigger mode needs to be enabled by setting the option value
UUCD_OPTION_EXT_TRIGGER to either EXT_TRIGGER_FALLING or
EXT_TRIGGER_RISING. Setting the option to EXT_TRIGGER_NONE disables external
trigger mode.
Exactly like in free-run mode, the application should invoke UUCD_StartCapture() and
then it can read frames by calling UUCD_GetFrame() until all the buffered frames are
transferred to a PC. In external trigger mode, the first UUCD_GetFrame() call may take
long time as it will be waiting for an external trigger to start video capture. Consider setting
long enough timeout by calling SetOption() with
UUCD_OPTION_FRAMEINFO_TIMEOUT parameter.
If UCD-2 devices are chained, the master device propagates the trigger to all slave devices.
All chained devices start video capture synchronously.
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