Campbell CR800 Series, Operator'S Manual, Page: 151 / 598

Section 7. Installation
151
Program Tasks
Measurement Task Digital Task Processing Task
•
Analog
measurements
•
Excitation
•
Read pulse
counters
(
Pulse()
)
•
Read control
ports
( GetPort() )
• Set control ports
( SetPort() )
•
VibratingWire(
)
•
PeriodAvg()
•
CS616()
• Calibrate()
•
SDM
instructions,
except
SDMSI04() and
SDMI016()
•
CDM
instructions / CPI
devices.
•
Pulse counters
•
Processing
•
Output
• Serial I/O
•
SDMSIO4()
• SDMIO16()
• ReadIO()
•
WriteIO()
•
Expression evaluation
and variable setting in
measurement and SDM
instructions
7.6.3.12.1 Pipeline Mode
Pipeline mode handles measurement, most digital, and processing tasks
separately, and, in many cases, 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,
the sequence in which the instructions are executed may not be in the order in
which they appear in the program. Therefore, conditional measurements are not
allowed in pipeline mode. Because of the precise execution of measurement
instructions, processing in the current scan (including update of public variables
and data storage) is delayed until all measurements are complete. Some
processing, such as transferring variables to control instructions, like PortSet()
and
ExciteV()
, may not be completed until the next scan.
When a condition is true for a task to start, it is put in a queue. Because all tasks
are given the same priority, the task is put at the back of the queue. Every 10 ms
(or faster if a new task is triggered) the task currently running is paused and put at
the back of the queue, and the next task in the queue begins running. In this way,
all tasks are given equal processing time by the CR800.
All tasks are given the same general priority. However, when a conflict arises
between tasks, program execution adheres to the following priority schedule:
1. Measurements in main program
2. Auto self-calibration