Category Archives: Communication Protocols

PTP Power Profile Explained (IEC/IEEE 61850-9-3)

Digital substations require time synchronization accurate to better than 1 microsecond. Sampled Values, GOOSE, sequence-of-events recording, traveling-wave fault location, and synchrophasor measurements all rely on precise time across the entire substation network. Standard IEEE 1588v2 (PTP) is powerful but too flexible — it has dozens of options and many possible configurations. To get interoperable, reliable, sub-microsecond timing in… Read More »

What Is a Merging Unit? IEC 61850 Process Bus Explained

A complete reference for substation engineers covering Merging Units — IEC 61869-9 specification, processing delay limits, sample rates, variant codes, SmpSynch values, conformance classes, holdover mode, PTP/1PPS synchronization, procurement template, and field troubleshooting Quick Reference Item Value What it does Digitizes CT/VT signals and publishes Sampled Values on the process bus Standard IEC 61869-9:2016 (replaces 9-2LE guideline) Transport… Read More »

OPC UA NodeId Explained: Namespace Index, Identifier Types, and Format

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 »

PROFINET Port Numbers Explained: UDP 34962/34963/34964, Ethertype 0x8892, and Firewall Configuration

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 »

Modbus Exception Codes Explained: Complete Reference Guide

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 Port Number Explained: TCP 4840, Discovery, and Firewall Configuration

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 »

IEC 60870-5-104 Type IDs Explained: Complete Reference Guide

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 »

CIP Object Model Explained: Classes, Instances, Attributes, and Services

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 Conformance Classes Explained: CC-A, CC-B, CC-C (IRT), and CC-D (TSN)

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 »

PROFINET GSD/GSDML Files Explained: What They Are and How to Use Them

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 »