Online editing a MicroLogix 1400 over EtherNet/IP can fail with “Program could not be compiled. Online edit error” when a MUL rung uses a literal constant such as 0.7 against an integer source. The same project may verify offline without complaint. The controller’s online edit compiler enforces stricter operand rules than the offline path, and floating literals in arithmetic instructions are a frequent tripwire.

Replace the literal with a Float file address that already holds 0.7, then retest the online edit before changing anything else.

Symptom and configuration

Root cause

Online edits on MicroLogix 1400 validate operand size and type more tightly than offline compilation. A floating constant as Source B is accepted in some offline verifications yet rejected when the edit must compile into the running image. Related offline messages such as “Operand size does not match” point to the same family of type mismatches. Not every MicroLogix change is online-legal; some structural edits still require offline modification and download.

Corrective procedure

1. Identify an unused Float address (example F8:7).
2. Preset F8:7 to 0.7 while offline or via a one-time MOV/initialization rung.
3. Edit the MUL: Source A remains N7:2; Source B becomes F8:7; Destination remains N7:7 or moves to a Float if precision matters.
4. Accept the online edit and confirm the rung compiles.
5. Force a known Source A value and verify the product at runtime.

MUL
  Source A: N7:2
  Source B: F8:7   <-- Float address, not literal 0.7
  Dest:     N7:7   <-- or F8:8 for full precision

Data-type consequences

With N7:2 = 10 and multiplier 0.7, an integer destination yields 7 after rounding/truncation behavior—not a preserved 7.0 Float. Choose the destination type deliberately when the value feeds PID, scaling, or compares.

Related arithmetic online-edit constraints

The same online compiler sensitivity appears on DIV, CPT-style expressions where available, and mixed INT/Float chains that were entered quickly during a live tweak. Engineers often try three consecutive online edits—changing only the constant, then the destination file type, then the entire rung—without ever leaving Run. Each failed compile leaves the pending edit queue in a confusing state. Cancel the failed edit cleanly, make one coherent change (literal to Float address), and accept once. If the MicroLogix reports that the program could not be compiled after several attempts, go offline, verify the file exists (F8 created with adequate elements), then download a known-good image before retrying online work.

Also confirm that the Float file is not protected by a data-table privilege or password that permits offline verification but blocks online modification. Series A and Series B MicroLogix 1400 controllers both support online editing when firmware and RSLogix 500 revisions align; mismatched tool versions can surface the identical “online edit error” text for unrelated reasons. Keep a bench controller image that demonstrates a successful Float-operand MUL so technicians can compare against the plant project.

Verification and wider constraints

After the edit accepts, force N7:2 through several values and trend or watch both the integer and Float destinations if both exist. Confirm online edit compiles without error, verify the MUL executes correctly in runtime, and if precision matters move the destination to a Float such as F8:8. Persistent failures after replacing literals should be reproduced offline first, then downloaded. Prefer addressed values instead of inline constants wherever live edits are expected. Keep MicroLogix programming practices documented beside other PLC and PAC standards so technicians do not chase Ethernet faults for what is an operand rule.