for attempt in range(3): try: value = instrument.read_register(0, 0, 3) # function code 3 break except minimalmodbus.NoResponseError as e: print(f"Attempt attempt+1 failed: e") time.sleep(0.5) instrument.serial.flushInput()
In RS485, if two devices talk simultaneously, you get partial frames → bytes missing.
The error is frustrating but rarely fatal. In 80% of cases, the solution is a simple configuration tweak—adjusting the Response Timeout or Interframe Delay in Modbus Poll. The remaining 20% involve wiring, termination, or hardware faults that are straightforward to diagnose with a systematic approach. modbus poll bytes missing error fixed
This is perhaps the most common reason for this specific error when using Ethernet gateways.
: In half-duplex RS-485, the master might "hear" its own request, confusing its byte count. : In Modbus Poll, check the "Remove Echo" for attempt in range(3): try: value = instrument
Industrial automation relies heavily on steady communication. When using Modbus Poll to test your network, seeing a error breaks your data stream. This error means your master software sent a request, but the returning data packet was shorter than expected.
Reflections on long RS-485 lines distort trailing edges of data packets. The remaining 20% involve wiring, termination, or hardware
If the error follows the slave device, the problem is likely in its firmware, configuration, or processing speed. Advanced Troubleshooting: Analyzing Modbus Frames
Adjusting the software timing parameters gives your hardware breathing room to complete the transmission. Open .
Timing errors mimic byte-missing conditions, especially if the slave is slow to compute or the network path includes wireless links.
How to Fix Modbus Poll "Bytes Missing" Errors: A Complete Troubleshooting Guide