Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 47)

Organize tags Chapter 2
A tag name follows this format.
Where Is
Name Name that identifies this specific tag.
Element Subscript or subscripts that point to a specific element within an array.
• Use the element identifier only if the tag or member is an array.
• Use one subscript for each dimension of the array. For example: [5], [2,8], [3,2,7].
To indirectly (dynamically) reference an element, use a tag or numeric expression that provides the element number.
• A numeric expression uses a combination of tags, constants, operators, and functions to calculate a value. For example, Tag_1-Tag_2,
Tag_3+4, ABS (Tag_4).
• Keep the value of the tag or numeric expression within the dimensions of the array. For example, if a dimension of an array contains 10
elements, then the value of the tag or numeric expression must be
0…9 (10 elements).
Member Specific member of a structure.
• Use the member identifier only if the tag is a structure.
• If the structure contains another structure as one of its members, use additional levels of the.Member format to identify the required
member.
Bit Specific bit of an integer data type (SINT, INT, or DINT).
Index To indirectly (dynamically) reference a bit of an integer, use a tag or numeric expression that provides the bit number.
• A numeric expression uses a combination of tags, constants, operators, and functions to calculate a value. For example, Tag_1-Tag_2,
Tag_3+4, ABS(Tag_4).
• Keep the value of the tag or numeric expression within the range of bits of the integer tag. For example, if the integer tag is a Dint (32-bits),
then the value of the index must be 0…31 (32-bits).
An alias tag lets you create one tag that represents another tag.
• Both tags share the same value.
• When the value of one of the tags changes, the other tag reflects the change
as well.
Use aliases in the following situations:
• Program logic in advance of wiring diagrams.
• Assign a descriptive name to an I/O device.
• Provide a simpler name for a complex tag.
• Use a descriptive name for an element of an array.
Address tag data
Alias tags
Rock well Automati on Publication 1756- PM004E -EN-P - October 2014 47