The master and slave must talk at the same speed. If the slave is set to 19200 baud and your Modbus Poll tool is set to 9600, bytes will arrive too slowly, causing the master to think bytes are missing.
| Error Context | Primary Fix | |---------------|--------------| | Random bytes missing | Check baud rate & noise | | All responses truncated | Increase response timeout | | Bytes missing after long idle | Adjust inter-character timeout | | Only large requests fail | Reduce register count per poll | | Works on USB but not RS485 | Add termination & biasing | modbus poll bytes missing error fixed