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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.
Direct TTL trigger Trigger signals can be received in TTL format directly through
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-Plus form factor does not support a TTL
trigger.