Cross Reference and Element Usage

Use one of the following methods to view the Cross Reference window:

·Choose the menu command View > Cross Reference

·Click on the Cross Reference button in the Navigation Bar

To access the Cross Reference table, the Byte Usage table, or the Bit Usage table, click on the appropriate tab at the bottom of the Cross Reference window: :

This topic discusses the following subjects:

Cross Reference Table

Byte Usage Table

Bit Usage Table

Cross Reference Table

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Tip: You must compile your program in order to view the Cross Reference table.

Use the Cross Reference table when you want to know whether a symbolic name or memory assignment is already in use in your program, and where it is used. The Cross Reference list identifies all operands used in the program, and identifies the POU, network or line location, and instruction context of the operand each time it is used.

Element refers to the operands used in your program. You can toggle between symbolic and absolute view to change the representation of all operands. (Use the menu command View > Symbolic Addressing.)

Block refers to the POU where the operand is used.

Location refers to the line or network where the operand is used.

Context refers to the program instruction where the operand is used.

Example of a LAD Cross Reference List

Example of an FBD Cross Reference List

Example of an STL Cross Reference List

Byte Usage Table

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Tip: You must compile your program in order to view the Byte Usage table.

The Byte Usage table allows you to see which bytes, from which memory areas, have been used in your program. It also helps you recognize duplicate-assignment errors.

b Indicates that a bit of memory has been assigned.

B Indicates that a byte of memory has been assigned.

W Indicates that a word (16 bits) has been assigned.

D Indicates that a double word (32 bits) has been assigned.

X Used for timers and counters.

Example 1: Interpreting the Byte Usage Table

This example of a Byte Usage table shows that its associated program makes use of the following memory locations: one bit within MB0; Counter C30; Timer T37.

Example 2: Recognizing Duplicate Assignment Errors

This example program makes overlapping memory assignments beginning at MB10.0.

The Byte Usage table can be examined to identify improper assignments. Since a double word requires 4 bytes, there should be 4 adjacent Ds in the row for VB0. Likewise, since a word requires 2 bytes, there should be 2 adjacent Ws for VB0. The row for MB10 reflects the same problems, plus the fact that MB10.0 was used in more than one assignment statement.

Bit Usage Table

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Tip: You must compile your program in order to view the Bit Usage table.

The Bit Usage table allows you to see which memory addresses, down to the bit level, have been used in your program. It also helps you recognize duplicate-assignment errors.

b Indicates that a bit of memory has been assigned.

B Indicates that a byte of memory has been assigned.

W Indicates that a word (16 bits) has been assigned.

D Indicates that a double word (32 bits) has been assigned.

X Used for timers and counters.

Example 1: Interpreting the Bit Usage Table

This example of a Bit Usage table shows that its associated program makes use of the following memory locations: from byte I0, bits 0,1,2,3,4,5, and 7; from byte Q0, bits 0,1,2,3,4, and 5; from byte M0, bit 1.

Example: Recognizing Duplicate Assignment Errors

This example program makes overlapping memory assignments beginning at MB10.0.

The Bit Usage table can be examined to identify improper assignments. In a properly assigned program, there would never be a bit value in the midst of the byte. BBBBBBBb is invalid, whereas BBBBBBBB would be valid. The same is true of the word assignment (there should be 16 adjacent Ws) and the double word assignment (there should be 32 adjacent Ds).

See Also:

Communication Configuration

PLC Type Selection

System Block (PLC Configuration)

Errors

Toggle between symbolic and absolute view

Getting Started Contents

Application User Reference