Nematron Pointe Controller - Manual (Page 109)

Pointe Controller User Guide Chapter 5: Developing Controller Programs
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5.1.3 The Scan Cycle
When a PointeControl project is executed on the controller, all of the Flow
Charts, Ladder Diagrams, and I/O points that make up the project are “scanned at
a specified speed and in a specified order.
Inputs, charts, ladders and outputs are processed in a fixed sequence; each cycle
through this sequence is called a logic scan. The general execution sequence is:
1. Get input values from all Pointe Controller modules and save to
corresponding tags in the Logic Memory database.
2. Execute all Flow Charts and Ladder Diagrams. Update input and output
tags as necessary.
3. Extract output values from Logic Memory database and send to Pointe
Controller modules.
Charts and Ladders are run in the order they are placed in the scan list . Only
charts and ladders in the list will be executed. You can mix Flow Charts and
Ladder Diagrams in the list to get the order you want. For example, if a ladder
program is processing inputs and generating values to be processed by a chart,
place the ladder first in the list followed by the chart.
To configure the interval for scanning the Flow Charts and Ladder Diagrams, see
“
Setting your project's scan interval ” on page 180.
To configure the scan intervals for individual I/O modules and operator panels,
see “
Specifying your installed hardware ” on page 121.
NOTE: It is possible to create a project that scans so quickly, using up so much
processor power on the controller hardware, that the PointeControl Monitor
cannot reattach to the controller. For more information, see “
Selecting and
attaching a controller ” on page 185.