The slave’s response includes a Byte Count field. If the slave is misconfigured, it may report the wrong length.
This is the "stutter" of the industrial world. If there is a delay between individual bytes within a single packet, Modbus Poll gets confused.
Ensure all devices share a common Signal Ground (SG or GND terminal), not just D+ and D-. 4. Reduce Data Volume Per Request modbus poll bytes missing error fixed
Sometimes, it is helpful to isolate whether the issue lies with the Master (PC/Modbus Poll) or the Slave (Field Device).
Ground potential differences introduce data corruption that clips packets. 2. Incorrect Timing Configuration The slave’s response includes a Byte Count field
If the issue persists, try another Modbus master software, such as ModScan or CAS Modbus Scanner. This will help you determine if the problem is with Modbus Poll itself or something else in your setup.
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 there is a delay between individual bytes
Here is a comprehensive guide to identifying and fixing the most common causes of missing bytes in your Modbus communication. 1. Protocol Mismatch: RTU over TCP vs. Native TCP
In Modbus RTU, when you send a query (e.g., Read Holding Registers), the slave should reply with:
If your RX line cuts off immediately after the Function Code or Byte Count, your slave device is either losing power mid-transmission, resetting, or failing to handle the requested register range. Summary Checklist to Fix "Bytes Missing" in Windows Device Manager. Increase Response Timeout to 2500ms in Modbus Poll. Verify Stop Bits: Use 2 Stop Bits if Parity is set to None.