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Appendix C Configuration Aspects for Programmers
NetScan User’s Manual C-21
Acquisition Buffer Interrogation
Note: In the following sections “current trigger block” always refers to the trigger block that is currently
being read.
The current status of the acquisition buffer may be interrogated at any time by issuing the Buffer Status String
(U6) command. As mentioned earlier, the U6 command is a user query command which will return information
regarding the current state of the acquisition buffer. The acquisition buffer holds scan data that has been
initiated by one or more trigger events. This data is held in trigger blocks within the buffer. Each trigger block
defines one acquisition that has taken place. An acquisition consists of the following:
•
pre-trigger scans (optional)
•
post-trigger scans
•
post-stop scans (optional)
The trigger blocks may be variable in length. The Buffer Status String command provides the interface in which
the current trigger block configuration may be queried.
The Buffer Status String is queried with the U6 command, returning 10 fields as indicated by the following
figure and corresponding list. The values in the figure represent a U6 response when the acquisition buffer is
empty.
1 - Number of Trigger Blocks Available This field represents the total number of trigger blocks currently
contained within the buffer. A block need not be complete to be included in this total, it only needs to be
triggered. If their are no trigger blocks available, Blocks Available will be 0000000.
2 - Number of Scans Available This field represents the total number of scans available at the time the U6
command was issued. It should be noted that pre-trigger data is not available to the user until the defined trigger
event has taken place. This total represents the total number of scans available across all trigger blocks in the
acquisition buffer. If their are no scans available in the buffer, Scans Available will be 0000000.
3 - Current Read Pointer This field represents the current position within the current trigger block. This
pointer is relative to the trigger point, which is always oriented at location 0. If, pre-trigger scans are being read,
the Current Pointer will be less than 0. Likewise, if post-trigger scans are being read, the Current Read Pointer
will be greater than 0. If the current scan to be read is the trigger scan, the Current Read Pointer will be
00000000. If the Current Read Pointer is undefined, its value will be -0999999.
4 - Trigger Time and Date Stamp This field represents the Time/Date that the trigger event occurred for the
current trigger block. This field takes on the same format as other time/date trigger stamp fields described
elsewhere in this manual. If the trigger event has not occurred, this field will have the value
00:00:00.00,00/00/00.
5 - Stop Event Pointer This field represents the location in the current trigger block that the stop event
occurred. This pointer will always be relative to the trigger point with the trigger point always oriented at
location 0. Since the stop event must always occur after the trigger event this pointer will always be greater than
0. If the stop event has not yet occurred at the time of the U6 query, this field will have the value of -0999999.
6 - Stop Event Time and Date Stamp This field represents the Time/Date that the stop event occurred for the
current trigger block. This field takes on the same format as other time/date stamp fields described elsewhere in
this manual. If the stop event has not yet occurred at the time of the U6 query, this field will have the value
00:00:00.00,00/00/00.