1

Hardstop Detected

Allen-Bradley · MicroLogix 1400 Programmable Controllers

What does 1 mean?

This error is generated whenever a hard stop condition is detected by the PTOX subsystem, indicating that a physical limit or emergency stop input has been activated. This error does not fault the controller.

Common Causes

  • Physical limit switch activation on the controlled axis.
  • External condition triggering a hard stop input to the PTOX subsystem.
  • Incorrect configuration of hard stop monitoring causing false triggers.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Scan the PTOX instruction on a false rung to acknowledge the error condition.

  2. 2

    Reset the EH (Enable Hard Stop) bit to 0 in the PTOX configuration to clear the error.

  3. 3

    Inspect the physical hard stop sensor and its wiring to ensure it is not falsely triggering or stuck in an activated state.

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Verified technical data. Last updated: March 2026

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Source: Allen-Bradley MicroLogix 1400 Programmable Controllers