Matrox Electronic Systems II manual Edge-triggered monoshot acquisition The VIA Video

62 Chapter 5: Matrox Meteor-II hardware reference

Trigger

Matrox Meteor-II /Multi-Channel accepts an external trigger input which allows image acquisition to be synchronized to external events. The board can operate in one of two modes, and the selected mode is specified by the DCF.

Matrox Meteor-II /Multi-Channel can operate in next valid frame/field mode When in this mode, the digitizer waits for the next valid frame or field (as specified by the DCF file) before commencing the grab. This trigger mode functions in one of three ways:

	■	Edge-triggered monoshot acquisition: The VIA (Video
		Interface Asic) waits for the rising/falling* edge to capture a
		single frame.
	■	Edge-triggered continuous acquisition: The VIA waits
		for the rising/falling* edge to start a continous grab.
	■ Level-sensitive "continuous" acquisition: The VIA grabs
		continuously while the level of the trigger is high/low*.
	* The polarity of the active and inactive levels of the trigger
	signal are software programmable.
	Matrox Meteor-II /Multi-Channel can also operate in
	asynchronous reset mode. In this mode, the digitizer resets the
	camera to begin a new frame when the trigger signal is received.
	Trigger signals can be received in TTL format directly through
Direct TTL trigger
	the video-input connector on the PCI form factor. The TTL level
	signal must have a maximum amplitude of 5 V. A signal over
	2 V is considered high while anything less than 0.8 V is
	considered low. The transition of 0.8 V to 2 V is considered to
	be the rising edge.

The trigger signal’s pulse width must be greater than one pixel. You can determine the pulse width by taking the inverse of the pixel frequency. For example, if the pixel frequency is

12.27 MHz, the minimum pulse width is 1/12.27 MHz ≈ 82 nanoseconds.

Note the PC/104-Plusform factor does not support a TTL trigger.