Modbus Poll Bytes Missing Error Fixed

If the slave device responds with only 15 bytes, or if the data packet is interrupted, Modbus Poll throws the error. Common Manifestations: Modbus Poll Error: Bytes Missing Timeout Errors preceding a "Bytes Missing" message. Wrong Data Length messages. Causes and Solutions for Modbus Poll Bytes Missing

Go to Setup -> Read/Write Definition in Modbus Poll. Increase the Response Timeout (e.g., from 500ms to 1000ms or 2000ms). If the slave is slow, it needs more time.

Mismatched baud rate, parity, or stop bits [2].

The slave’s response includes a Byte Count field. If the slave is misconfigured, it may report the wrong length. modbus poll bytes missing error fixed

If the error occurs sporadically (e.g., when a large motor starts), it is likely EMI.

Use Modbus Poll’s "Log to File" feature. Review the log weekly for intermittent byte loss that might indicate a degrading cable.

Incorrect parity or stop bits corrupt frames, causing Modbus Poll to misinterpret byte count. If the slave device responds with only 15

By systematically checking these layers—from the physical wire to the software timeout—you can stabilize your connection and eliminate the "Bytes Missing" error.

Use a tool like or Wireshark (with a serial sniffer) to view the raw hex bytes. Look for incomplete frames:

Verify that your termination and biasing resistors are installed correctly, especially on the ends of long network runs. Step 5: Test with Another Device or Software Causes and Solutions for Modbus Poll Bytes Missing

Install 120Ω termination resistors at both physical ends of the RS485 chain.

Modbus RTU uses to frame messages. If noise or slow slave causes extra gaps, Modbus Poll may split the response.