72
•
Xtium2-CXP PX8 Reference
Xtium2-CXP PX8 User's Manual
Virtual Frame Trigger for Line Scan Cameras
When using line scan cameras, a frame buffer is allocated in host system memory to store
captured video lines. To control when a video line is stored as the first line in this “virtual” frame
buffer, an external frame trigger signal is used.
For fixed length frames, the Sapera vertical cropping parameter controls the number of lines
sequentially grabbed and stored in the virtual frame buffer.
For variable length frames, the External Frame Trigger (when a level or dual input type is
selected) controls the number of lines sequentially grabbed up to the maximum of lines in the
virtual frame buffer.
For both fixed and variable length frames, choosing an active low/high or dual input permits
grabbing multiple consecutive images as long as the chosen signal is active. This action is also
called “rolling over” to the next buffer. When choosing a single rising or falling edge, a single frame
will be acquired; there is never any roll over.
External Frame Trigger Detection
Fixed Frame
Variable Frame
Active Low/High
Roll Over
Roll Over
Rising/Falling Edge
No Roll Over
No Roll Over
Dual Input Rising/Falling Edge
Roll Over
Roll Over
Virtual Frame Trigger Timing Diagram
The virtual frame trigger signal (generated by some external event) connects to the Xtium2-CXP
PX8 trigger input.
•
Virtual frame trigger can be differential (RS-422) or single ended (TTL, 12V, or 24V) industry
standard, and be rising or falling edge active, active high or low, or double pulse rising or falling
edge.
•
In this example, virtual frame trigger control is configured for rising edge trigger.
•
Virtual frame trigger connects to the Xtium2-CXP PX8 via the External Trigger Input 1 & 2
inputs.
•
Camera control signals are active at all times. These continually trigger the camera acquisition
in order to avoid corrupted video lines at the beginning of a virtual frame.
•
The camera control signals are either timing controls on Xtium2-CXP PX8 shaft encoder inputs,
or line triggers generated internally by the Xtium2-CXP PX8.
•
The Sapera vertical cropping parameter specifies the number of lines captured.