Phytec eGrabber-4plus, Руководство по оборудованию

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Driver Software
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PHYTEC Meßtechnik GmbH 2004 L-608e_4
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Since the user program defines the address regions it knows the
position of the memory regions and might mark them by a pointer. In
this way the access to the data can be accomplished without using the
driver.
The driver provides information of the status, which indicates the end
of the storage of the image in the memory, so that at this time all data
are available.
This mechanism guarantees a fast access to the data. The process is
real time regarding to the standard TV format. For the digitizing of a
field it takes a time of 20 msec and the digitizing of a whole frame
lasts 40msec. In some cases a time delay must be added to get the total
time from the demand of the image to the end of the digitization
process. Initially this is the wait time until the beginning of the desired
half image.
This additional time might arise from waiting for the appropriate field.
For example, if an even field is demanded, but the camera has just
started scanning an even field, so it is necessary to wait until this field
and the next following odd field are finished. In the worst case a delay
of 40msec (two fields) can be expected. Now the demanded field can
be digitized, which will last another 20msec. During the following
20 msec nothing will happen in this memory region since the odd field
will be received. The next 20msec a new even field is stored in the
memory. It must be considered that the old information will be
overwritten by the new information, otherwise the content might be
interpreted incorrectly by the software especially for moving scenes.
In this case the wait time is almost 40 ms (two half images,
worst case).
The image is subsequently digitalized and is complete 20 ms later. For
the next 20 ms nothing occurs in this memory space, since during this
time the odd-image is delivered.