Nematron Pointe Controller - Manual (Page 131)

Pointe Controller User Guide Chapter 5: Developing Controller Programs
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5.6 Building and Editing Flow Charts
Flow Charts depict various types of information and control processing problems
and their means of solution. Charts consist of symbols having a given
signification, brief explanatory text, and connecting lines. Each symbol relates to
an unambiguous and meaningful name that is consistent throughout the charts.
The connecting lines show the path of execution through the chart.
Multiple Flow Charts
A single Flow Chart ideally performs a single task; however, a total system
solution requires the execution of multiple tasks, often simultaneously.
PointeControl solves this problem by providing concurrent execution of any
number of separate Flow Charts. With multiple charts executing concurrently,
each chart focuses only on its specific task, which greatly simplifies the chart
structure.
The PointeControl Framework creates a Chart List that specifies which charts are
executed and the order in which the charts are executed. At startup, the Pointe
Controller unit performs all initialization procedures then begins the normal scan
cycle. During each cycle, the system performs an input scan to read data from the
configured modules, executes each chart specified in the Chart List, and performs
an output scan to write data to the modules.
All charts execute during each cycle — starting with the first chart in the chart list
and proceeding through the entire list. In the most basic cycle, the first chart in
the list runs, then the second chart in the list, then the third, until all charts have
run. However, in many real world situations, the chart being executed reaches a
block where it must wait for some event to occur before it can proceed. While
waiting, the chart (typically) yields control to the next chart in the list, allowing
that chart and all other charts to continue executing as normal. During the next
execution cycle, if the event has occurred, the chart continues execution from
that point; otherwise, the chart again yields control to the next chart.
Program and Subcharts
The PointeControl Framework provides two levels of flowchart development:
Program and Subchart. Program charts describe the steps needed to perform a
particular control task or process. The more precise a Program chart, the easier it
is to develop function flowcharts.
Subcharts contain the more detailed information necessary to make the chart
function. You can use these powerful reusable subprograms many times in several
different flowcharts.