Campbell Scientific CR1000 Measurement and Control System - Manual (Page 133)

Section 7. Installation
133
Instructions or commands that are handled by each sequencer are listed in table
Task Processes
(p. 133).
The measurement task sequencer is a rigidly timed sequence that measures
sensors and outputs control signals for other devices. The digital task sequencer
manages measurement and control of SDM
devices. The processing task
sequencer converts analog and digital measurements to numbers represented by
engineering units, performs calculations, stores data, makes decisions to actuate
controls, and performs serial I/O communication.
The CR1000 executes these tasks in either pipeline or sequential mode. When a
program is compiled, the CR1000 evaluates the program and determines which
mode to use. Mode information is included in a message returned by the
datalogger, which is displayed by the support software. The CRBasic Editor pre-
compiler returns a similar message.
Note A program can be forced to run in sequential or pipeline modes by placing
the SequentialMode or PipelineMode instruction in the declarations section of
the program.
Some tasks in a program may have higher priorities than other tasks.
Measurement tasks generally take precedence over all others. Priority of tasks is
different for pipeline mode and sequential mode.
Table 15. Task Processes
Measurement Task Digital Task Processing Task
• Analog
Measurements
• Excitation
• Read Pulse
Counters
•
Read Control
Ports (GetPort())
•
Set Control Ports
(SetPort())
• VibratingWire()
• PeriodAvg()
• CS616()
• Calibrate()
• All SDM
instructions, except
SDMSI04() and
SDMI016() • Processing
• Output
• Serial I/O
•
SDMSIO4()
•
SDMIO16()
•
ReadIO()
•
WriteIO()
• Expression evaluation and
variable setting in
measurement and SDM
instructions
7.7.3.6.1 Pipeline Mode
Pipeline mode handles measurement, most SDM, and processing tasks separately,
and possibly simultaneously. Measurements are scheduled to execute at exact
times and with the highest priority, resulting in more-precise timing of
measurement, and usually more-efficient processing and power consumption.
Pipeline scheduling requires that the program be written such that measurements
are executed every scan. Because multiple tasks are taking place at the same time,