Campbell Scientific CR6 CR6 Measurement and Control System - Page 157

SlowSequence / EndSequence, 8.3.7.3 SubScan / NextSubScan, 8.3.7.4 Scan Priorities

Page 157 highlights

Section 7. Installation • Count - number of scans to make before proceeding to the instruction following NextScan. A count of 0 means to continue looping forever (or until ExitScan). In the example in CRBasic example Scan Syntax, the scan is one second, three scans are buffered, and measurements and data storage continue indefinitely. 7.8.3.7.2 SlowSequence / EndSequence Slow sequences include automatic and user entered sequences. Background calibration is an automatic slow sequence. User-entered slow sequences are declared with the SlowSequence instruction and run outside the main-program scan. Slow sequences typically run at a slower rate than the main scan. Up to four slow-sequences scans can be defined in a program. Instructions in a slow-sequence scan are executed when the main scan is not active. When running in pipeline mode, slow-sequence measurements are spliced in after measurements in the main program, as time allows. Because of this splicing, measurements in a slow sequence may span across multiple-scan intervals in the main program. When no measurements need to be spliced, the slow-sequence scan will run independent of the main scan, so slow sequences with no measurements can run at intervals ≤ main-scan interval (still in 1 ms increments) without skipping scans. When measurements are spliced, checking for skipped slow scans is done after the first splice is complete rather than immediately after the interval comes true. In sequential mode, all instructions in slow sequences are executed as they occur in the program according to task priority. Background calibration is an automatic, slow-sequence scan. Read More Self-Calibration (p. 327) 7.8.3.7.3 SubScan() / NextSubScan SubScan() / NextSubScan are used in the control of analog multiplexers (see the appendix Analog Multiplexers (p. 596) for information on available analog multiplexers) or to measure analog inputs at a faster rate than the program scan. SubScan() / NextSubScan can be used in a SlowSequenc / EndSequence with an interval of 0. SubScan cannot be nested. PulseCount or SDM measurement cannot be used within a sub scan. 7.8.3.7.4 Scan Priorities in Sequential Mode Note Measurement tasks have priority over other tasks such as processing and communication to allow accurate timing needed within most measurement instructions. A priority scheme is used in sequential mode to avoid conflicting use of measurement hardware. As illustrated in figure Sequential-Mode Scan Priority Flow Diagrams (p. 159), the main scan sequence has the highest priority. Other sequences, such as slow sequences and calibration scans, must wait to access measurement hardware until the main scan, including measurements and processing, is complete. 157

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Section 7.
Installation
Count
— number of scans to make before proceeding to the instruction
following
NextScan
. A count of
0
means to continue looping forever (or until
ExitScan
). In the example in CRBasic example Scan Syntax
,
the scan is one
second, three scans are buffered, and measurements and data storage continue
indefinitely.
7.8.3.7.2 SlowSequence / EndSequence
Slow sequences include automatic and user entered sequences.
Background
calibration is an automatic slow sequence.
User-entered slow sequences are declared with the
SlowSequence
instruction and
run outside the main-program scan. Slow sequences typically run at a slower rate
than the main scan. Up to four slow-sequences scans can be defined in a program.
Instructions in a slow-sequence scan are executed when the main scan is not
active. When running in pipeline mode, slow-sequence measurements are spliced
in after measurements in the main program, as time allows. Because of this
splicing, measurements in a slow sequence may span across multiple-scan
intervals in the main program. When no measurements need to be spliced, the
slow-sequence scan will run independent of the main scan, so slow sequences
with no measurements can run at intervals
main-scan interval (still in 1 ms
increments) without skipping scans. When measurements are spliced, checking
for skipped slow scans is done after the first splice is complete rather than
immediately after the interval comes true.
In sequential mode, all instructions in slow sequences are executed as they occur
in the program according to task priority.
Background calibration is an automatic, slow-sequence scan.
Read More
Self-Calibration
(p. 327)
7.8.3.7.3 SubScan() / NextSubScan
SubScan()
/
NextSubScan
are used in the control of analog multiplexers (see the
appendix
Analog Multiplexers
(p. 596)
for information on available analog
multiplexers) or to measure analog inputs at a faster rate than the program scan.
SubScan()
/
NextSubScan
can be used in a
SlowSequenc / EndSequence
with
an interval of
0
.
SubScan
cannot be nested.
PulseCount
or SDM measurement
cannot be used within a sub scan.
7.8.3.7.4 Scan Priorities in Sequential Mode
Note
Measurement tasks have priority over other tasks such as processing and
communication to allow accurate timing needed within most measurement
instructions.
A priority scheme is used in sequential mode to avoid conflicting use of
measurement hardware. As illustrated in figure
Sequential-Mode Scan Priority
Flow Diagrams
(p. 159),
the main scan sequence has the highest priority. Other
sequences, such as slow sequences and calibration scans, must wait to access
measurement hardware until the main scan, including measurements and
processing, is complete.
157