How to find every place a tag is used, and the one rung that writes it
The output isn't coming on. The coil is there, but something upstream is false, or another rung turns it off again. The fastest way in is the tag itself: where is it written, and where is it read?
In Studio 5000, right-click a tag and choose Go to Cross Reference (or press Ctrl+E) to list every routine and rung that uses it, with the instruction and whether it reads or writes. Without Studio 5000, Rungview builds the same cross-reference from an .ACD or .L5X: click any tag in a rung or the tag table, and it lists every use, marked read or write, one click from the rung.
Reads and writes
A tag is written by output instructions: OTE, OTL, OTU, the destination of MOV or math, a timer or counter structure. It is read by conditions: XIC, XIO, compares, the source of a move. When troubleshooting, find the writes first. If a BOOL is written by an OTE in two different rungs, the last one scanned wins, which is a classic bug.
In Studio 5000
Right-click the tag in a rung or in the tag editor and choose Go to Cross Reference. The window lists container, routine, rung and instruction, and a destructive flag for writes. Double-click a line to jump there.
In Rungview
Type the tag name in Find tag, or click it anywhere in a rung. A panel lists each use as program / routine / rung with the instruction and a read or write badge. Click a line to jump to the rung; the tag is highlighted wherever it appears in the drawing. The cross-reference covers ladder and Structured Text, so a tag set in an ST routine still shows up.
Tracing a permissive back
Start at the output that won't energise. Click each condition on its rung, look at where that tag is written, and repeat. Three or four hops usually land on the real cause: a sensor input, a fault latch, or a mode bit nobody reset.
Find the rung that writes it
Click any tag and see every read and write. Free for L5X files.
Get Rungview
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FAQ
Does the cross-reference include UDT members?
Uses like Motor.Run are indexed under the base tag Motor, so you see every use of the structure.
Does it cover add-on instructions?
Calls to an AOI are indexed with their arguments. Logic inside source-protected AOIs isn't visible.
Is the cross-reference free?
Yes, for any L5X. For an .ACD it comes with Pro.