Before fixing the problem, you must understand the Modbus frame structure.
RS485 networks require proper termination to prevent signal reflections that corrupt data. Place -ohm resistors at both ends of the RS485 bus.
Polling too fast (e.g., every 100ms) can overwhelm a slave device. Try increasing the Scan Rate to 1000ms or higher to see if the error clears. modbus poll bytes missing error fixed
What could cause such micro-interruptions? Mara’s eyes drifted to the power supply racks. They shared a route with the RS-485 bus, and last month a new VFD had been installed near Slave 12. VFDs were notorious for generating EMI if not filtered or grounded correctly. She walked the route at different times, watching the VFDs shift motor speeds as production loads changed. At moments when the VFD switched frequency, tiny spikes appeared on her oscilloscope across the bus lines.
Route data cables away from high-voltage motor wires and VFDs. 4. Correct the Read and Write Definitions Before fixing the problem, you must understand the
Do not replace your slave. Do not blame the cable. First, apply the (the single most effective solution). Then, adjust your inter-frame timing. In 95% of cases, the error will vanish permanently.
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later. Polling too fast (e
This 2,500-word guide leaves no stone unturned. We will diagnose the root causes of the "Bytes Missing" error and provide eight proven, actionable fixes—from wiring corrections to advanced serial timing tweaks.
This is the most powerful diagnostic technique. Use a Serial Port Monitor like or similar to capture the raw data exchange at the byte level. This will show you exactly what requests Modbus Poll sends and what responses it receives, allowing you to quickly spot framing errors, incorrect CRC values, or the point where the communication breaks down.
If distance is an issue (>1000m), use a Modbus TCP to RTU gateway (e.g., Moxa MGate). Ethernet handles long distances without byte framing errors.