The "Bytes Missing" error in indicates that the software received a response from the slave device, but the packet length was shorter than what the Modbus protocol requires for that specific request .
This guide provides an updated, comprehensive troubleshooting approach for 2026 to resolve this issue by covering hardware, software, and communication parameter issues. Understanding the Error modbus poll bytes missing error
Check that RS-485 A/B (or +/-) is connected correctly. If using RS-232, ensure TX goes to RX and vice versa. The "Bytes Missing" error in indicates that the
Many modern "Bytes Missing" errors in 2026 are traced back to cheaper USB-to-RS485 converters that do not handle the RX/TX switching fast enough. Try reducing the Baud rate, or testing with a higher-quality, FTDI-based converter. Specific Scenarios Possible Cause Slave device hangs/needs reset. Check power supply, consider adding a delay between polls. Error 02 or Illegal Address Requesting too many registers or wrong address. Reduce "Length" or check map documentation. Consistent Bytes Missing Mismatch in baud rate or parity. Re-verify baud rate, stop bits, and parity. Echo Checkbox Issue Local loopback echoing requests. Uncheck "Remove Echo" in Modbus Poll settings. If using RS-232, ensure TX goes to RX and vice versa
The critical point: For example: