Instead of randomly changing settings, follow this structured process to isolate and resolve the issue.
Modbus is a request-response protocol. The Master sends a request and waits for a predefined .
Step 1: Verify Communication Parameters (The "Holy Trinity") modbus poll bytes missing error fixed
[Start] │ ▼ Verify Serial Port Parameters (Baud, Parity, Stop Bits) ──► Mismatch? ──► Fix Settings │ ▼ No Mismatch Isolate the Hardware (Connect PC directly to 1 Slave with a short cable) │ ▼ Error Persists? Increase Response Timeout to 3000ms & Lower USB Latency Timer to 1ms │ ▼ Error Persists? Check Data Traffic with Communication Log (Display > Communication...) │ ▼ Analyze Rx Frame: Are bytes physically missing, or is the CRC corrupted? │ ▼ Apply Termination Resistors / Check Cable Shielding Utilizing the Modbus Poll Traffic Log
Update the driver specifically to the official chip manufacturer version (FTDI or Prolific). Optimize Latency Timers Step 1: Verify Communication Parameters (The "Holy Trinity")
: Ensure you aren't receiving a "noisy" response from a different slave on the same bus.
Use Shielded Twisted Pair (STP) cable and ground the shield at one end only . Summary Checklist Potential Cause Reflections Add 120Ω termination resistors. Noise Use shielded cables; separate from power lines. Timing Increase Response Timeout in Modbus Poll. Framing Match Baud, Parity, and Stop Bits exactly. Hardware Replace cheap USB converters with FTDI-based ones. Check Data Traffic with Communication Log (Display >
In serial communications, some devices need a small delay after the request is sent before they can switch from "sending" to "receiving" mode. A Pre-Delay of 50ms often stabilizes the connection. 2. Hardware and Wiring Fixes
9/10 (loses 1 point for obscure setting naming)
Save your .mbp project file. You will change multiple settings.
Requesting data that does not exist causes the slave device to return partial error responses or truncate packets. Reduce Quantity Allocation Go to > Read/Write Definition .