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.
| Check | Action | | :--- | :--- | | Timeout | Increase Response Timeout to 2000ms+. | | USB | Lower USB Latency Timer to 1ms in Device Manager. | | Parity | Ensure Parity and Stop Bits match exactly (e.g., Even, 1 Stop). | | Cabling | Add 120-ohm termination resistors if cabling is long. | | Grounding | Ensure Master and Slave share a common signal ground. | modbus poll bytes missing error fixed
By systematically working through this list, starting with the Timeout and USB Latency, you will likely resolve the "Bytes Missing" error and establish a stable Modbus connection. Sometimes the slave reports a wrong byte count
Modbus Poll defaults to 1000 ms (1 second) timeout. But some slaves (especially older PLCs or wireless modems) need 1500–2000 ms. The old "fix" (increase to 3000 ms) worked sometimes but introduced latency. | Check | Action | | :--- |