Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 132
Execution and Task Priority
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Section 7. Installation 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 132