Section 7. Installation
7.6.3.12 Execution and Task Priority
Execution of program instructions is divided among the following three tasks:
• Measurement task — rigidly timed measurement of sensors connected
directly to the CR800
• CDM task — rigidly timed measurement and control of CDM/CPI
(p. 492)
peripheral devices
• Digital task (a.k.a, SDM task) — rigidly timed measurement and control
of SDM
(p. 513) peripheral devices, pulse measurements, and RS-232
measurements.
• Processing task — converts measurements to numbers represented by
engineering units, performs calculations, stores data, makes decisions to
actuate controls, and performs serial I/O communication.
Instructions or commands that are handled by each task are listed in table
Program Tasks
(p. 150).
These tasks are executed in either pipeline or sequential mode. When in pipeline
mode, tasks run more or less in parallel. When in sequential mode, tasks run
more or less in sequence. When a program is compiled, the CR800 evaluates the
program and automatically determines which mode to use. Using the
PipelineMode or SequentialMode instruction at the beginning of the program
will force the program into one mode or the other. Mode information is included
in a message returned by the datalogger, which is displayed by the datalogger
support software
(p. 86). The CRBasic Editor pre-compiler returns a similar
message.
Note A program can be forced to run in sequential or pipeline mode by
placing the SequentialMode or PipelineMode instruction in the
declarations section of the program.
Some tasks in a program may have higher priorities than others. Measurement
tasks generally take precedence over all others. Task priorities are different for
pipeline mode and sequential mode.
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