Section 7. Installation
132
the order calls are received. This may cause unexpected pauses in the conflicting
program sequences.
7.7.3.5.3 Incidental Sequences
Data table sequences are essential features of nearly all programs. Although used
less frequently, subroutine sequences also have a general purpose nature. The
following incidental sequences, however, are used only in applications to which
they specifically apply.
Shut-Down Sequences
The ShutDownBegin / ShutDownEnd instructions are used to define code that
will execute whenever the currently running program is shutdown by prescribed
means. More information is available in CRBasic Editor Help.
Dial Sequences
The DialSequence / EndDialSequence instructions are used to define the code
necessary to route packets to a PakBus® device. More information is available in
CRBasic Editor Help.
Modem-Hangup Sequences
The ModemHangup / EndModemHangup instructions are used to enclose code
that should be run when a COM port hangs up communication. More information
is available in CRBasic Editor Help.
Web-Page Sequences
The WebPageBegin / WebPageEnd instructions are used to declare a web page
that is displayed when a request for the defined HTML page comes from an
external source. More information is available in CRBasic Editor Help.
7.7.3.6 Execution and Task Priority
Execution of program instructions is prioritized among three task sequencers:
• Measurement
• Digital
• Processing
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 CR800 executes these tasks in either pipeline or sequential mode. When a
program is compiled, the CR800 evaluates the program and determines which
mode to use. Mode information is included in a message returned by the
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