Specifications

CR3000 Overview
ShortCut is included with PC200, PC400 and LoggerNet and is available for
free from the Campbell Scientific web site. The CRBasic Editor is included in
PC400 and LoggerNet.
OV2.3 Instruction Execution within the Datalogger
The execution of instructions within the datalogger is accomplished using three
separate task types: measurement, SDM, and processing. As it is named, the
measurement task handles measuring the signals received on the datalogger’s
wiring panel, as well as outputting signals for control of other devices. The
measurement and control hardware is manipulated on a rigidly timed sequence.
The SDM task handles the measurement and control of most SDM devices.
The processing task converts the raw signals read by the datalogger into
numbers representing engineering units, performs calculations, stores data,
makes the decisions to actuate controls, and performs serial I/O
communication.
Measurement Task
• Analog Measurements
• Excitation
• Read Pulse Counters
• Read Control Ports
(GetPort)
• Set Control Ports
(SetPort
• VibratingWire
• PeriodAvg
• CS616
• Calibrate
SDM Task
• All SDM instructions,
except SMDSIO4 and
SCMIO16
Processing Task
• Processing
• Output
• Serial I/O
• SDMSIO4
• SDMIO16
• ReadIO
• WriteIO
• Expression evaluation
and variable setting in
measurement and SDM
instructions
The datalogger can execute these tasks in either pipeline or sequential mode.
When a program is compiled the datalogger evaluates the program and
determines which mode to use. This information is included in a message
returned by the datalogger and is displayed by the support software.
CRBasic’s precompiler returns a similar message. A program can be forced to
run in sequential mode by placing the SequentialMode instruction in the
declarations section of the program.
OV2.3.1 Pipeline Mode
In pipeline mode, the measurement task, SDM task, and processing task are
three separate functions. In this mode the three tasks may operate
simultaneously. The measurement tasks are scheduled to take place at exact
times and with the highest priority when the datalogger starts each scan. This
results in a more precise timing of measurements, and may be more efficient
with processing and power consumption. However, this prescheduling of
measurements means measurement instructions must be executed every scan,
and because multiple tasks are taking place at the same time, the sequence in
which the instructions are executed may not be in the exact order in which they
appear in the program. For these reasons, conditional measurements are not
allowed in pipeline mode. Also note that because of the precise execution of
measurement instructions, processing for the measurements in the current scan
(including update of public variables and output to data tables) is delayed until
all measurements are completed.
OV-8