These four steps produce an L5X ready for Studio 5000 import. The full guide below covers every option in detail.
Overview
Logic Compare diffs two Allen-Bradley L5X exports. Each rung is classified as Unchanged, Added, Removed, or Modified, with modified rungs showing instruction-level diffs. An optional AI-generated summary describes the changes in plain English. The diff can be exported to PDF.
Common uses: reviewing a contractor’s edits before accepting delivery, comparing a running program against the last known-good backup after a production issue, or documenting changes between project milestones for change-control records.
The page shows two upload panels side by side with a VS divider. A Compare scope indicator in the top-right updates as you select routines. It shows Routine, Program, or Controller depending on whether selections live in one routine, one program, or span multiple programs.
Before you start. You need two L5X exports, typically a “before” version and an “after” version of the same routine or program. The AI summary consumes AI capacity; everything else runs as part of your Pro plan.
Step 1. Upload the two L5X files
Drag the older L5X into the left upload panel. Drag the newer L5X into the right panel. Left is conceptually “before”; right is “after”. The diff shows the right side compared against the left, so additions on the right appear as Added, content only on the left appears as Removed.
Each panel parses its upload and lists every routine it found, grouped by program. Pick which routines you want compared on each side (multi-select). The Compare scope indicator in the top-right reflects what you’ve selected:
- Routine. One routine on each side.
- Program. Multiple routines on one or both sides, all from a single program.
- Controller. Selections span multiple programs.
Routines with the same program::name on both sides match up automatically. A routine only on one side appears as fully Added or fully Removed in batch mode.
Step 2. Set normalization options
Click Options to expand the normalization controls. These determine which differences count as “real” changes vs. cosmetic noise.
| Option | Default | What it does |
|---|---|---|
| Ignore whitespace | On | Treats two rungs that differ only in spacing as identical |
| Instructions case-insensitive | On | Treats XIC vs xic as the same instruction (Logix treats them this way anyway) |
Both options are on by default so cosmetic-only differences never show up as modifications. Turn them off if you specifically want to surface spacing or case drift.
Step 3. Compare and review the diff
Click Compare Logic. Logic Compare runs the diff on the server and returns the result. Typical comparisons complete in seconds; very large multi-program comparisons may take a minute or two.
The diff view shows:
- A summary card at the top with counts (X added, Y removed, Z modified, N unchanged).
- An optional AI summary card if you enabled Include Summary (see below).
- The rung-by-rung diff below, side-by-side.
Reading the rung diff
Each rung is paired side-by-side: left pane is “before”, right pane is “after”. Color coding:
| Color | Meaning |
|---|---|
| No highlight | Unchanged (per normalization rules) |
| Green | Added: rung exists on the right only |
| Red | Removed: rung exists on the left only |
| Yellow / amber | Modified: same rung position, different content |
For modified rungs, instruction-level changes are highlighted so you can see exactly which operand, tag, or instruction type changed.
AI summary
The Include Summary checkbox to the right of the Compare button enables an AI-generated plain-English summary of the diff. It’s gated to Pro and above and consumes AI capacity from your plan; the tooltip on the checkbox surfaces the lock state and any “capacity reached” condition.
You can enable it before running Compare (the summary runs automatically after the diff completes) or click Generate Summary in the summary card after a comparison.
For most reviews, one summary per comparison is enough.
Step 4. Export the diff report
After a comparison, the rung-diff view has an Export PDF action with two modes:
- Context mode. Shows changed rungs plus a few surrounding rungs. Shorter, suitable for change reviews.
- Full mode. Shows every rung with the diff highlighted. Longer, suitable for archival or detailed reviews.
The PDF includes the summary card, the AI summary if generated, and the rung-by-rung visual diff. PDF filenames default to logic-compare_<routine_a>_vs_<routine_b>_<date>.pdf for single-routine mode or logic-compare_<file_a>_vs_<file_b>_<date>.pdf for batch mode.
There is no L5X export from Logic Compare. It is a viewer. To apply changes to a project, work in Studio 5000 directly or use Precision Replace for systematic transformations.
Common pitfalls
- Sides loaded backwards. Left is “before”, right is “after”. If you upload the new version on the left and the old on the right, the diff reads inside-out (additions look like removals). Use the Clear button on each panel to swap if needed.
- Routine matched as one Removed + one Added instead of Modified. When the diff matcher can’t align two routines (different name + different content), it splits into a removal and an addition. If routines were renamed between versions, compare them individually in single-routine mode so you can name both sides explicitly.
- Comparing files exported with different options. Two L5X exports from the same Studio 5000 project can differ if one was exported with Decorated Data on and the other off. The diff will pick up the metadata differences. Export both sides with the same options for a clean comparison.
- AI summary contradicts the structural diff. Rare but possible. The summary is generated from the diff but the AI can misinterpret intent. Treat the rung-by-rung diff as ground truth; treat the summary as a starting hypothesis.
- Big modified rung shown as Removed + Added. When a single rung changes too much for the matcher to consider them “the same rung,” it splits into a removal and an addition. Usually safe to read as one logical change.
FAQ
How big a comparison can it handle?
Routines up to a few hundred rungs diff in seconds. Whole-program comparisons across many routines take longer; the page streams a progress indicator. If a comparison genuinely doesn’t fit, split by program or by routine and compare in pieces.
Does Logic Compare work on Structured Text or Function Block routines?
The L5X parser reads ST and FB but the rung-level diff is optimized for ladder. ST/FB diffs come through as text-level changes without instruction-aware highlighting.
What about UDT or AOI changes?
UDT and AOI definition changes appear as Added or Removed at the data-type level rather than rung-level Modified. To see what changed inside an AOI’s internal routine, upload the AOI export on each side and compare it as a routine.
Can I compare an L5X against a Git history version?
Yes, by exporting both versions to disk. Check out the older commit, save the L5X as before.L5X; check out the newer commit, save it as after.L5X; upload both to Logic Compare.
Does the diff include comments?
Yes. Comment changes show up as Modified rungs. There isn’t a separate “ignore comments” toggle in the current build; if you only want logic changes, focus on the rungs with instruction-level highlighting and ignore the ones where only the comment text changed.
Can I share a PDF with someone who doesn't have a PLCflow account?
Yes. The PDF is a standalone file. It includes the diff summary, the AI summary (if generated), and the rung-by-rung visual diff. No PLCflow account required to view.
Related
- Code Analyzer. Run on both sides of the comparison to see whether quality improved or regressed across the change.
- Comment Helper. If one side has comments and the other doesn’t, document the uncommented side first so the diff is apples-to-apples.
Related modules
An AI-powered review built to find logic errors, copy-paste mistakes, and hidden bugs in your Studio 5000 L5X. Backed by a deterministic rule set, ranked by severity, with a PDF report for the review meeting.
Upload an L5X program. Pick a routine. Generate AI-drafted comments for every rung. Review, accept, edit, reject, then download a commented L5X for re-import into Studio 5000.
Honest feedback. We read all of it.