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fanuc-do-not-found-in-program-reference-position.md

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title FANUC DO Not Found in Program — Check Reference Position
domain fanuc
subdomain troubleshooting
tags
do
digital-output
reference-position
background-logic
space-function
search
source robot-forum.com
status published
confidence 0.9
created 2026-07-01
verified_date
domain_expert Nation

Problem

A digital output (e.g., DO[66]) is confirmed active on the robot, but searching all TP programs for "DO[66]" or "DO[" returns zero results. The output is being set somewhere, but not in any visible program code.

Root Cause

The DO is assigned to a Reference Position setting, not to program code. Reference positions can trigger DOs automatically when the robot reaches a configured position — this is configured outside of any TP program.

Other possible sources:

  • Background Logic (BG Logic) — not visible in standard program search
  • Space Function — position-based DO activation
  • Manual Macro (M[] markers)

Solution

Step 1: Check Reference Positions

MENU → SETUP → Reference Position

Each reference position can have:

  • Position definition (joint or Cartesian)
  • DO assignment (which output to activate)
  • Condition (within tolerance, etc.)

Step 2: Check Background Logic

MENU → SETUP → BG Logic

Look for DO assignments in BG Logic programs that run continuously.

Step 3: Check Space Functions

MENU → SETUP → Space

Space functions can activate DOs based on robot position within defined volumes.

Step 4: Search All Sources

-- Use program search with broader terms:
-- Search for the DO number in ALL program types
-- Including: TP, KAREL, BG Logic, Macro, Reference Position

Verification

  1. Navigate to MENU → SETUP → Reference Position
  2. Find the reference position that assigns DO[66]
  3. Modify or remove the DO assignment as needed
  4. Verify DO[66] behavior changes accordingly

Notes

  • "Solved, close the question" without posting the fix defeats the purpose of a forum — always share the solution
  • Reference Position DOs are invisible to standard program text search
  • This is a common gotcha for new FANUC users
  • Source: https://www.robot-forum.com/robotforum/thread/55076/