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 »
Every Modbus device comes with a register map. It is usually a table in the user manual or a separate PDF that lists all the data points the device makes available — voltages, currents, setpoints, alarms, status bits, and configuration parameters. Reading a register map sounds simple. But it is one of the most common sources of errors… Read More »
Every Modbus message contains a function code. It is a single byte that tells the slave device what operation to perform — read coils, write registers, or diagnose communication. The Modbus specification defines multiple function codes, but in practice you will use about six of them for 95% of your tasks. The rest are either rarely implemented, vendor-specific,… Read More »
Modbus was built in 1979 for a world where industrial networks were physically isolated. There was no internet, no remote access, and no reason to worry about authentication or encryption. The protocol was designed for reliability and simplicity — not security. That was fine for decades. But today, industrial control systems are increasingly connected to corporate networks, cloud… Read More »
Modbus TCP/IP brings the simplicity of the Modbus protocol onto modern Ethernet networks. Instead of serial cables and RS-485 wiring, you use standard Ethernet infrastructure — switches, routers, and Cat5e/Cat6 cables. The protocol works the same way as Modbus RTU at the application level. You still read holding registers, write coils, and use the same function codes. The… Read More »
Modbus RTU over RS-485 is the most common serial communication setup in industrial automation. It connects PLCs, sensors, drives, meters, and other field devices on a simple two-wire bus. The protocol itself is straightforward. But getting it to work reliably depends on getting the details right — wiring, termination, addressing, baud rate, parity, and register mapping all need… Read More »
Modbus is simple, but real SCADA integration is rarely simple. In power systems, automation, and industrial plants, most commissioning delays come from small configuration mistakes or physical-layer issues — not from the protocol itself. This guide explains 15 real Modbus problems engineers face on site, how to recognize them quickly, and what practical actions solve them. The explanations… Read More »
Modbus is a simple protocol, but the values inside registers can be displayed in many different ways. A single 16-bit register can represent: The challenge is that the Modbus protocol never tells you how to interpret the number. Only the device’s documentation explains the meaning. To decode Modbus data correctly, engineers must understand the different data type formats… Read More »
Modbus TCP/IP is one of the most widely adopted methods for connecting industrial devices over Ethernet networks. It is used in factories, power plants, water treatment facilities, building automation systems, and countless other fields where equipment must exchange information reliably. Even though modern automation protocols offer advanced features, Modbus TCP/IP remains extremely common because it is easy to… Read More »
Every Modbus TCP/IP device listens on TCP port 502. This single port carries all Modbus communication over Ethernet — read requests, write commands, exception responses, and diagnostics. Port 502 is registered with IANA (Internet Assigned Numbers Authority) under the service name “mbap” (Modbus Application Protocol). It has been the standard since the Modbus TCP specification was published in… Read More »