Instruction manual

Appendix B. FAQs
B.1. Common FAQs
B.1.1.
What is synchronous acquisition?
Synchronous acquisition means that all cameras run synchronously to each other. This is done by
applying a horizontal and a vertical sync signal to each camera. For the frame grabber family family
these signal have to be taken from the on-board sync generator. Using sync signals from an extra
camera is not possible.
In restart mode synchronous operation is achieved by using the h-sync signal for the horizontal
synchronisation. The vertical synchronisation is done by the trigger signal. One signal is used for all
cameras. The preferred trigger mode in synchronous operation is grabber trigger, where the trigger
signal is send to the grabber which send a trigger signal to the cameras that is synchronised to the
camera timing.
The synchronisation makes sure that the trigger signal is not applied to the cameras is critical timing
phases, where one camera might react immediately to the signal whereas an other camera starts its
restart timing one h-sync period later.
B.1.2.
What is asynchronous acquisition?
Asynchronous acquisition is only possible with the and grabbers. The data of all cameras can only
be stored as 8 bit per pixels b/w images. Up to fours cameras of the same type can be used and do
not have to be (and can not be ) synchronised to each other. To control the progress of the
acquisition of the four channels the function of some el_Test.... and el_Wait... functions have been
changed. Please refer to the API documentation for details, because some of these functions do not
work at all and some have a slightly different function.
In the restart mode a trigger signal for each camera has to be provided. Please refer to the
hardware documentation to see which jumpers have to be set and at which inputs the signals have
to be applied.
B.1.3.
What are DMA channels?
A DMA channel moves data from a source on the grabber to a buffer in the memory. Data sources
on the grabber are fed by one or more ADCs which digitise the input signals. Before the
transmission the data source packs the ADC values into long words according to the packing mode
(e.g. red, green and blue in one word for RGB transmission, 4 b/w pixel for monochrome
transmission or 2 b/w pixels each blown up to 16 bit RGB pixel with identical blue red and green
values for pseudo RGB mode)
The connection of a DMA channel to a buffer is done with el_AssignBuffer. The packing mode of the
buffer determines the way the image data is packed at the source. If the packing mode of the target
buffer is not supported by the data source or the buffer is not large enough for the acquired image
an error is generated.
It is possible to connect several DMA channels to one buffer (but not vice versa). Normally this does
not make sense because the data of the two buffers overwrite each other. It happens sometimes by
accident if the buffer is connected to a new channel without switching off the previously used
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