F81

Comm Loss

Allen-Bradley · PowerFlex 4M Adjustable Frequency AC Drive

What does F81 mean?

Communication over the drive's RS-485 (DSI) port has ceased, meaning the drive is no longer able to send or receive data from connected serial devices. This can lead to loss of control or monitoring via the serial interface.

Complete Troubleshooting Guide

  1. 1

    Inspect the RS-485 (DSI) wiring for breaks, loose connections, or incorrect polarity between the drive and the connected communication device.

  2. 2

    Verify the communication adapter or port expander (if used) is correctly installed, powered, and functioning. Replace if necessary.

  3. 3

    Confirm that the communication partner (e.g., PLC, HMI) is active and attempting to communicate with the drive. Check its settings and status.

  4. 4

    If the disconnection was intentional, adjust C304 [Comm Loss Action] to a setting that allows the drive to continue operation or handle the loss gracefully, rather than faulting.

Source: Allen-Bradley Manual