Home Assistant Modbus ‘No Response’ but QModMaster Works You wired up a Modbus device — say, an Aqotec controller behind a Waveshare RS485-to-Ethernet gateway — and QModMaster reads its registers without a hitch. Then Home Assistant logs No response received from the remote unit or Unable to decode response, and nothing updates. This exact “QModMaster…
Modbus Values Off by 10x? Scale Factor & Offset QModMaster shows 2355 but your inverter’s display says 235.5 V. Or a temperature reads 1025 when the room is clearly 25 °C. Before you blame the wiring, the address, or the byte order — check the two most boring explanations in Modbus: scale factors and offsets….
Arduino + MAX485 Timeout? DE/RE Control Fix Here’s the classic maker trap: your Arduino Modbus slave sketch answers perfectly when the PC talks to it over a USB-to-TTL cable — every read in QModMaster succeeds. Then you swap in a MAX485 module for real RS485, and QModMaster just says timeout, no response. The sketch didn’t…
Modbus 32-bit Integer Wrong? Word Swap (CDAB) Fix Your energy meter says it exported 1,234 kWh, but QModMaster shows 80,889,344. Or a counter reads fine until it crosses 32,767 and suddenly goes negative. If the raw registers look plausible but the 32-bit value is exactly 65,536× too big (or the sign flips), you are looking…
Modbus Polling Too Fast? Slow Slave Overload Fix Everything works for a while — then the device stops answering, the link drops, and only a restart brings it back. If that pattern sounds familiar, you may not have a wiring problem at all. You may be polling a slow device faster than it can cope…
Duplicate Modbus Slave IDs: Find Bus Collisions Your bus works fine most of the time — then readings jump, CRC errors appear out of nowhere, and one device only misbehaves when another is powered on. Before you blame the cable, check the simplest cause with the weirdest symptoms: two devices on the same bus configured…
QModMaster Blurry on High-DPI Displays? Fixes If QModMaster looks fine on an old 1080p monitor but turns into a blurry, cramped mess on your 4K laptop screen, you are not alone. A SourceForge reviewer put it bluntly: “Windows GUI is unusable on a high-dpi display… controls are scaled properly but positioned with hardcoded pixel counts.”…
QModMaster Scan Rate: Fix Timeouts on Slow Devices Your device answers every manual read in QModMaster, but the moment you enable Scan mode — continuous polling — it starts timing out, drops off the bus, or needs a power cycle to come back. The device isn’t broken. You’re just asking it questions faster than it…
QModMaster via Modbus TCP Gateway: Multiple Slaves Unit ID Guide Your Modbus TCP gateway answers on its IP address, QModMaster reads slave 1 just fine, but slaves 2, 3 and 4 all time out. Or worse — every slave you query returns slave 1’s data. This is the single most common gateway problem in the…
Modbus Float Shows the Wrong Value? Fix the Byte Order You read a floating-point value from your device and get 2.40e-41 instead of 123.0. Or a negative number with 33 digits. The connection is fine, the registers respond — the value is just garbage. Nine times out of ten, this is a byte order problem,…
