Rockwell Automation 2711E PanelBuilder 1400e Modbus Communications - Manual (Page 28)

4–5 Defining Communications
Publication 2711E-6.12 – November 1997
Any tag that has Device as its data source must be assigned to a scan
class. At runtime, the PanelView terminal periodically updates its tag
information by scanning the device addresses. You determine how
often a tag value is updated by assigning the tag to a scan class that
you have configured in the Scan Classes editor. Make sure that tags
with rapidly changing device values are assigned to a fast scan rate,
while those that don’t change often are scanned less frequently. This
helps optimize traffic flow on the Modbus network. Proper use of
scan classes can reduce traffic on the Modbus network.
You should already have determined the rates for the scan classes
when you completed the Communications worksheet. If not, see
Chapter 2, “Planning Applications,” in the PanelBuilder 1400e
Configuration Software for Windows User Manual, for tips on
assigning foreground and background scan rates.
To open the Scan Class Editor dialog box:
" Open the PLC Communications folder and choose Scan Classes,
or choose from the toolbar.
The Scan Class Editor opens.
To configure scan classes:
1. Fill in the following information for each scan class. Use the
information you recorded in the Communications worksheet.
Name—A Through K
You can keep the letter for the name of the scan class or you can
type a name up to 20 characters long. The name can have upper
and lower case letters, numbers, dashes, and underscores. You
cannot use spaces.
If you type a meaningful name, it will be easier to keep track of
what the scan classes represent. For example, you might name
one scan class TimeCritical, another SlowChanging, and so on.
Configuring Scan Classes