The error would appear when the received frame length didn’t match the expected byte count based on the function code + register count. In my case, the inverter sometimes responded with a 3-byte delay between the slave address and CRC. Modbus Poll’s older parser was too strict—it timed out between bytes, assuming the frame was truncated. The result: dropped data, retries, and logging gaps.
Sometimes the slave reports a wrong byte count in its response header. For example, the slave says Byte Count = 20 but sends 18 data bytes. Modbus Poll is correct to flag bytes missing. Here, the "fix" is not on the poller but on the slave firmware.
Common Modbus RTU settings: 8 data bits, Even parity, 1 stop bit (8E1). If your slave uses 8N2 (No parity, 2 stop bits), the master’s frame synchronization will fail. modbus poll bytes missing error fixed
In Modbus RTU, when you send a query (e.g., Read Holding Registers), the slave should reply with:
"Bytes Missing" means:
Actual received bytes < Expected bytes (based on Byte Count field) The error would appear when the received frame
Common symptom: Partial data, timeouts, or repeated retries.
Isolate the problem:
Before applying fixes, it helps to understand why the packet is incomplete. The error usually stems from one of three categories:
To fix the error, identify your trigger from this list: Common Modbus RTU settings: 8 data bits, Even
In Modbus Poll, go to Display > Communication or View > Log. The log will show:
