PLC Modbus Error

A PLC Modbus Error means that communication with the PLC has reported a protocol error. Modbus can use different transports; Ethernet-connected MyVends installations should be checked as Ethernet communication paths rather than assumed to be serial wiring.

PLC readings may stop updating and remote commands may be unavailable while communication is affected. This does not establish that every independently connected device has stopped reporting.

What to check

  1. Record the exact error message or code, machine name, and time.
  2. Check the machine's online status, PLC status, and recent logs. See PLC Disconnected if the PLC connection is also down.
  3. Check the installed communication path and visible cable connections without changing module switches or addressing.
  4. If the error persists, especially a repeated device-busy/code-6 message, contact support before changing the PLC, ECOM configuration, or restarting equipment.

If support recommends a power cycle, follow the procedure for your machine and verify that readings update and commands work afterward. Include the PLC and communication-module models when requesting help.

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