Measurement Computing TempScan/1100 - Manual (Page 92)

5-2 System Operation 889897 TempScan / MultiScan User's Manual
Buffer Organization
Single Trigger Block
Each Trigger Block in the buffer has an associated Trigger Block descriptor, used by internal processes for
Acquisition Buffer maintenance. The management of this Trigger Block descriptor is totally user-
transparent and, since the Trigger Block descriptor takes up memory, it will have an indirect affect on some
user-defined processes. For instance, the Buffer 75% Full and the Buffer Overrun conditions will happen
on a fewer number of scans as the trigger blocks increases.
A Trigger Block becomes defined when the configured Trigger (trigger start event) occurs. Once this start
event occurs, the data within the Trigger Block (including any Pre-Trigger data) is available to be read
(even though the Trigger Block may not yet be complete). Scan data is written then read to the Trigger
Block in a FIFO fashion. As the controller requests written (or buffered) scan data, the TempScan/1100 or
MultiScan/1200 unit supplies the oldest available scan data. After the scan data is supplied and read, that
scan data is erased and is no longer available from the unit, and the Read Pointer automatically advances in
the current Trigger Block. Consequently, the next scan data in the sequence, if acquired, now becomes the
oldest available scan data. There is no mechanism to allow jumping around in the buffer or going back to a
scan that had already been read by the controller.
Since scans are written into the Trigger Block sequentially, the Trigger scan may appear at any location
within the Trigger Block. The TempScan/1100 or MultiScan/1200 will automatically convert these physical
scan locations to logical scan locations where the Trigger scan is always oriented at location
0
. The
placement of the Trigger scan at the origin facilitates the quick interpretation of the Read Pointer and gives
a frame of reference for other locations within the trigger block. If Pre-Trigger scans are configured, they
will have logical scan locations defined by negative integers, whereas Post-Trigger scans will have logical
scan locations defined by positive integers. All Trigger Block pointers are relative to the Trigger scan.
From this point on, manual text discussions will assume references to logical Trigger Blocks only.
To retrieve the scan data after a Trigger has occurred, the TempScan/1100 or MultiScan/1200 provides
multiple query functions. The Read Buffered Data (
R
) command provides the following queries: Read the
oldest scan data in the Acquisition Buffer (
R1
), Read the oldest complete Trigger Block in the acquisition
buffer (
R2
), and Read all of the scan data available in the Acquisition Buffer (
R3
). The following User
Status (
U
) command query – Query the Buffer Status String (
U6
) – queries the current Trigger Block for a
variety of information, including the current number of Trigger Blocks available in the buffer, and the
current number of scans available in the buffer.
Multiple Trigger Blocks (Auto Re-arm)
Multiple Trigger Blocks are allocated sequentially, and the scans within each Trigger Block are written and
read sequentially. Hence, after the last scan of the first Trigger Block is read by the controller, the first scan
of the next Trigger Block will be read next. Through the Auto Re-arm capability, it is possible to capture
more than one Trigger Block in the Acquisition Buffer of the TempScan/1100 or MultiScan/1200. The
Trigger can only be re-armed after a Trigger Block has been completed and written. Each Trigger Block
will contain one and only one Trigger (trigger start event).
If the Auto Re-arm feature is disabled, a Set Trigger Configuration (
T
) command must be issued to re-arm
the TempScan/1100 or MultiScan/1200 for acquisition. To disable the Auto Re-arm feature, you must issue
a Set Trigger Configuration (
T
) command with the
re-arm
flag set to zero.
If the Auto-Rearm feature is selected, another acquisition will take place on the next Trigger without any
controller intervention. This allows the TempScan/1100 or MultiScan/1200 to store several acquisitions
continuously in its buffer. The logical scan locations of the Trigger points, and their associated time
stamps, can be found in the Buffer Status String. The Read Pointer is always on the oldest Trigger Block,
so requests for Read Pointer status will always correspond to the Trigger Block available to be read.
However, the next Trigger must be initiated after the previous acquisition has been completed and written.
Otherwise, a Trigger overrun will occur.
Note: While armed, the Auto Re-arm feature does not allow you to change the acquisition
configuration.