Protocols — troubleshooting procedures

Reference and troubleshooting guides for industrial protocols: Profinet, EtherNet/IP, EtherCAT, Modbus, OPC UA, MQTT, CC-Link IE, IO-Link, CANopen, and more. Browse by protocol.

3 published procedures.

• Modbus TCP — Won't Connect, or Connects and Lies

  You will be able to split a Modbus TCP fault into "no socket" versus "wrong map" in under a minute, then fix the Unit ID, the 40001 off-by-one, the wrong function code, or the swapped 32-bit word order — reading the exception code to tell you which.

• EtherNet/IP — Implicit Connection Timeouts and Faults

  Read an EtherNet/IP I/O drop the way the protocol actually fails: a connection that was refused at the door, or one that was accepted and then starved. After this you can name the cause from the fault code alone, size an RPI without overloading a device, and decide whether IGMP is really your problem.

• OPC UA — Client Cannot Connect: The Certificate Trust Handshake

  You will be able to work out, in under ten minutes, which side of an OPC UA connection refused the other and why — untrusted certificate, wrong Application URI, wrong hostname, expired certificate, or a security policy mismatch — and fix it without breaking the clients that still work.