is correct, use shielded cables, and verify that the 120-ohm termination resistor is at both ends of the bus. Baud Rate & Serial Mismatch
If the master and slave are not running at the exact same baud rate, parity, or stop bits, the data will be interpreted incorrectly, causing the serial port to cut off the message prematurely.
If all parameters match and the physical wiring is sound, the issue may be specific to the software environment. modbus poll bytes missing error fixed
: Use the Display > Communication window in Modbus Poll to see the raw Hex strings. Look for the RX (receive) line to see if the slave is actually sending fewer bytes than requested.
Some cheap Modbus slaves have a hidden buffer limit. Try reading instead of 125. In Modbus Poll: Setup > Read/Write Definition > Quantity: reduce from 125 to 10. If the error disappears, the slave has a firmware bug. Use consecutive shorter reads. is correct, use shielded cables, and verify that
If you request more registers than the slave device has available, some slaves will send an incomplete response or an exception code that Modbus Poll struggles to parse, resulting in a "Bytes Missing" flag.
: Modbus RTU requires a silence of at least 3.5 characters to signal the end of a frame. If your serial-to-USB converter or the slave device has "jitter," the frame might be cut off prematurely. Ensure the Baud Rate and Parity settings match exactly on both ends. Electrical Noise & Interference : : Use the Display > Communication window in
When you send a standard query (e.g., 01 03 00 00 00 0A CRC ), the valid response must follow this structure:
Cheap FTDI or Prolific clones fail to handle fast buffer flushing.
Most "Bytes Missing" errors are resolved by giving the hardware more time to process frames. Open Modbus Poll.