Glossary · PLC and control programming
Cross-reference
Also known as: Cross-reference list, Where-used list
German: Querverweis
In PLC programming tools, a cross-reference is a list showing every place in a project where a variable, address, block or other object is used, and whether it is read or written there.
- PLC programming
- Technical documentation
In one sentence
A cross-reference lists every place in a PLC project where a variable, address or block is read or written.
Example
Before changing the meaning of the tag Conveyor1_Run, the programmer opens the cross-reference and finds it written in one block and read in five others.
How it applies
- Engineering: Cross-references show where a signal comes from and where it goes. A variable written in more than one place is a typical warning sign that the tool's cross-reference reveals quickly.
- Maintenance: When a machine stops, technicians start from the missing output, use the cross-reference to find the network that writes it and follow the conditions back to the input that is missing.
- Change management: Before a variable, block or I/O address is changed, the cross-reference is the basis for an Impact analysis: every place listed may behave differently afterward.
- Documentation: Exported cross-reference lists and the Symbol table belong in the software documentation of the delivered version. In manuals, the same idea applies to text: a reference to a signal name should match the name used in the program.
Cross-reference in code vs. in documents
In a PLC tool, a cross-reference is generated from the program. In documentation, a cross-reference is a link from one place in a text to another, for example in DITA via a DITA content reference (conref) or a related link. Both serve the same purpose: making dependencies visible so that a change in one place is not missed elsewhere.