Fix “Number of Registers Returned Does Not Match” in QModMaster When QModMaster asks a slave for N registers, it sanity-checks the reply: for function codes 03 and 04, the response’s Byte Count field must equal exactly 2 × N (two bytes per 16-bit register). When it doesn’t, QModMaster reports: “number of registers returned does not…
Fix “Read Data Failed: Timeout” in QModMaster If QModMaster greets you with “Read data failed. Error: timeout” — or its close cousin, “Read data failed. System exception [Unknown error]” — the message is simpler than it looks: QModMaster sent your request, waited, and nothing usable came back. The request left fine; the reply never arrived….
Modbus Exception Codes 01/02/03/04 Explained (+ Fixes) An exception response is actually good news: it proves your wiring, baud rate, slave ID, and CRC are all correct — the device heard you perfectly and is refusing on purpose. You can recognize one in the bus monitor: the response function code is the request code plus…
Modbus CRC Errors: Causes and Fixes Every Modbus RTU frame ends with a 16-bit CRC — a checksum the receiver recomputes and compares. Match: the frame is accepted. Mismatch: the frame is silently discarded, and QModMaster reports a CRC error. A CRC error never means your data was “almost right” — it means the frame…
QModMaster ‘No Response’ Timeout: 9 Fixes That Actually Work “No response” is the most common thing QModMaster ever tells you — and the least informative. It means a request went out (or didn’t) and nothing usable came back within the timeout. The cause is almost never QModMaster itself. Work through these nine fixes in order;…
RS485 RTS Control in QModMaster: When to Enable It Your wiring is right, the baud rate matches, the slave ID is correct — and QModMaster still reports “no response”. Before you rewire anything, check one setting: RTS control. On half-duplex RS485 it decides whether your PC is allowed to talk at all. Why RS485 needs…
Modbus Addressing: 0-Based vs 1-Based (The 40001 Trap) If you have ever typed 40001 into QModMaster’s Start Address field and gotten nothing back — no data, a timeout, or an “illegal data address” exception — you have hit the most common addressing mistake in Modbus. It is not a bug in QModMaster. It is two…
