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Kepware Knowledge Base: Solution

Unable to Communicate with a MicroLogix PLC

Last Update: 11/12/2018

KEPServerEX cannot communicate to an Allen-Bradley Micrologix PLC. The server's Event Log is either displaying an error message that includes an error code or the error message "Device Not Responding."

1. If the error code states that users are unable to read or write to registers, then the error is coming from the PLC. For more information, refer to the driver's help file.

2. If the error message "Device Not Responding" is received, the problem may be one of the following:

  • Bad cabling. To fix, use the same cable that was used to program the PLC.
  • Bad communication settings. To fix, match the settings configured in RSLogix. Use 8 data bits in the server: the PLC does not support 7 data bits.
  • An invalid Device ID. A MicroLogix PLC's Device ID is decimal; an SLC5 PLC's Device ID is octal. Users familiar with SLC5 PLCs may have used octal out of habit.

3. If using Ethernet Encapsulation, verify the following:

  • The communication settings in the Serial to Ethernet Converter match the settings that worked in the direct connection from the PC to the PLC.
  • The converter's IP address falls within the subnet of the PC. A socket connection cannot be made to an IP that is outside of the subnet.
Related Protocols
Allen-Bradley DF1