ORTEC DSPEC 50, Руководство пользователя по оборудованию

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APPENDIX E. LIST MODE IN THE DSPEC 50
The DSPEC 50 is equipped with List Mode , which streams spectroscopy data directly to the
computer, event-by-event, without the data “dead periods” associated with the acquire-store-
clear-restart cycle of standard spectrum acquisition. To enter List Mode, issue the SET_MODE_
LIST command; use SET_MODE_PHA to exit List Mode.
This appendix provides details about the List Mode that will enable experienced programmers,
using the ORTEC C
ONNECTIONS
Programmer’s Toolkit with Microsoft
®
ActiveX
®
Controls
(A11-BW) to write custom software applications for acquiring and saving List Mode data. List
Mode data can also be acquired and saved to file using Maestro and GammaVision.
E.1. List Mode Data
In List Mode, each detectable event that would normally be histogrammed as a spectrum is sent
to the computer in the form of a pulse-height value along with a time stamp that indicates the
time the pulse arrived. The data can be analyzed by the computer in real time to determine if
some significant event has occurred, or can be streamed to disk for analysis at a later time. In
either case, the computer is intimately involved in the collection of the data.
Each request for List Mode data is returned with a minimum of 4 and a maximum of 16384 32-
bit words. Each request for data returns a block of 32-bit list mode words that begin with a 32-
bit integer number of valid bytes followed by a 3-word C
ONNECTIONS
time stamp, thus the
minimum of 4 words in a request. The first word is the number of bytes returned, not including
the first 4 bytes. The minimum value returned here is 12, for the three C
ONNECTIONS
time stamp
words only, and the maximum is 65532, indicating 3 C
ONNECTIONS
time stamp words plus
16383 data words.
The C
ONNECTIONS
time stamp represents the 64-bit Windows file time that corresponds to the
exact time that the request for data is sent to the spectrometer. At the exact time the C
ONNEC
-
TIONS
requests data from the spectrometer, the spectrometer creates a hardware time word in the
list mode data stream that indicates the corresponding time within the spectrometer. The 16-bit
real time number on the hardware time word is from the same time source as the 16-bit real time
stamps on each of the ADC words. Using the C
ONNECTIONS
time stamp and the hardware time
word you can determine the 64-bit Windows time associated with each ADC word in the buffer.
Refer to the Win-32 function GetSystemTimeAsFileTime() for more information about the
64-bit time format contained in these words.
In the case where the data acquisition program does not get all of the data from the spectrometer,
the data block will not contain a hardware time word. In this case the data acquisition program
must immediately request another block of data from the spectrometer in order to find the
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