Guides
Common field communication problems, explained byte by byte.
Reading Modbus RTU frames — request, response, exception, CRC
Decode «01 03 00 00 00 02 C4 0B» byte by byte: address, function, start, quantity, CRC, exception replies and the 40001 notation.
Read →USB-serial adapter latency — why frames split and replies arrive late
USB adapters batch received bytes instead of passing them on at once. How the FTDI 16 ms latency timer affects Modbus RTU framing and replies, and what to do.
Read →RS-485 wiring checks — five things to look at when replies are missing or garbled
A/B polarity, termination, biasing, common ground and topology. RS-485 wiring problems and their symptoms, before you blame the software.
Read →No reply from a Modbus device — a checklist for RTU and TCP
Every request times out? Narrow it down by what comes back, then check slave ID, baud, parity, wiring, IP, port, unit ID and the device's Modbus settings.
Read →Modbus addresses: 0-based vs 40001 notation — from manual to wire
The same first register is written 0, 1, 40001, 400001 or 0h0001 depending on the manual. How to get the 0-based wire address, with real manual examples.
Read →Modbus function codes — 01–06, 0F, 10 and 17, and when to use each
The nine Modbus functions that read and write coils and registers in one table: quantity limits, reply layouts, 06 vs 10, 05 vs 0F, and what exception 01 means.
Read →Reading Modbus floats and 32-bit values — finding the word order
Float32 and U32 values span two registers, and which comes first is up to the device. Find ABCD or CDAB with a known value; see what wrong orders look like.
Read →Modbus TCP not connecting — checking port 502, unit ID and connection limits
Ping works but Modbus TCP does not? Check layer by layer — network, port 502, MBAP reply, values — for subnet, firewall, port, unit ID and connection limits.
Read →RS-232 vs RS-422 vs RS-485 — choosing by wiring, distance and node count
All serial, but electrically different: single-ended vs differential, point-to-point vs multidrop, 2-wire vs 4-wire, distance, node count, how to choose.
Read →4–20 mA basics and troubleshooting — 2-wire, 4-wire, live zero, open loop
Why the signal starts at 4 mA, 2-wire vs 4-wire wiring, scaling, and how NAMUR NE 43 failure currents (3.6, 21 mA) tell open loops from sensor faults.
Read →Pt100 2-, 3- and 4-wire connections, and choosing a thermocouple type
In a Pt100, lead resistance becomes error — 1 Ω is about 2.6 °C. 2-, 3- and 4-wire, tolerance classes, thermocouple types K to B, cold-junction compensation.
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