Rockwell Automation 2711E PanelBuilder 1400e Modbus Communications - Manual (Page 53)

6–16 Defining Tags
Publication 2711E-6.12 – August 1997
Important: For Modbus analog tags, the entire controller data file
element assigned to the tag’s address is used in
determining the tag’s value. This is true regardless of
the tag’s data type. For example, a Byte data type
assigned with the address 30001 will still look at the
entire 16 bits of the integer element, even though the
tag is interested only in the lower 8 bits. The
controller’s logic must ensure that the unused bits are 0,
to prevent invalid or out of range data from being read
from the address.
Device Data Source
A tag with Device as its data source reads or writes its data to or
from a device on the Modbus network. If you have not configured
the node and scan class for the tag, you can configure them from the
Tag Database editor while you are defining a tag, or you can
configure them after you have finished creating tags. If you want to
define them after the tag is created, make sure any one of the node,
scan class, or address fields is blank so that Accept will not validate
and expect a valid tag record complete with supporting node and
scan class definitions.
Validation
Tags are validated when you choose Accept, and any errors must be
corrected before the tag definition will be saved. Validation ensures
that any node and scan class definitions needed by the tag exist.
Specifying Device as the Data Source
Use the information on the Device Tags worksheets to fill in the tag
addresses.
1. Choose Device.