A merging unit is the device that sits between conventional instrument transformers and the digital world of IEC 61850. It takes the analog current and voltage signals from current transformers and voltage transformers, samples them at a precise rate, time-stamps each sample, and publishes them onto the process bus as digital Sampled Values. Every protection IED, bay controller,… Read More »
Every node in an OPC UA address space — every variable, object, method, and data type — has a unique address called a NodeId. When you read a tag value, browse the address space, or call a method, you are using a NodeId. NodeIds are the OPC UA equivalent of register addresses in Modbus or class/instance/attribute paths in… Read More »
A complete reference for PROFINET ports — covering UDP 34962 (RT Unicast), UDP 34963 (RT Multicast), UDP 34964 (RPC Context Manager), UDP 49152, the Ethertype 0x8892 for cyclic I/O, MRP Ethertype 0x88E3, firewall rules, and Wireshark filters Introduction PROFINET ports are different from every other industrial protocol. Unlike Modbus (port 502), DNP3 (port 20000), or IEC 104 (port… Read More »
A practical reference for engineers covering every Modbus exception code (01, 02, 03, 04, 05, 06, 08, 0A, 0B) — what each code means, what causes it, how to fix it, and how to identify exception responses in Wireshark Introduction When a Modbus master sends a request to a slave, four things can happen: This article covers case… Read More »
OPC UA uses TCP port 4840 by default. This single port carries everything OPC UA does — discovery, session establishment, reading tags, writing values, subscriptions, method calls, and historical data access. Unlike OPC Classic (which used DCOM with dynamic port allocation and was a firewall nightmare), OPC UA uses one well-known port that works cleanly through NAT, proxies,… Read More »
Every ASDU (Application Service Data Unit) in IEC 60870-5-104 contains a Type ID — a single byte that defines what kind of data the message carries. It tells the receiving station whether the message contains a single-point indication, a measured value, a command, a counter, or a system message. The Type ID is the first byte of every… Read More »
Every CIP device — whether it is an Allen-Bradley PLC, a variable frequency drive, a remote I/O module, or a safety controller — organizes its data using the same object model. Understanding this model is the key to configuring, programming, and troubleshooting any CIP-based device. CIP (Common Industrial Protocol) does not use register maps like Modbus. Instead, it… Read More »
PROFINET is one protocol — not three. But it comes in four conformance classes that define what a device can do, how fast it communicates, and what network infrastructure it needs. Engineers often confuse PROFINET RT, PROFINET IRT, and PROFINET IO as separate protocols. They are not. They are all part of PROFINET IO, defined in IEC 61158… Read More »
Every PROFINET device comes with a GSD file. Without it, your PLC does not know the device exists. It cannot configure modules, exchange I/O data, or read diagnostics. GSD stands for General Station Description. In PROFINET, GSD files are written in XML format. The language used is called GSDML — General Station Description Markup Language. The file extension… Read More »
Every piece of data in an IEC 61850 system lives inside a logical node. A circuit breaker position is inside XCBR. An overcurrent trip signal is inside PTOC. A voltage measurement is inside MMXU. A GOOSE control block is inside LLN0. Logical nodes are the building blocks of the IEC 61850 data model. They represent functions — not… Read More »