Modbus Poll Bytes Missing Error Fixed -

Guide: Fixing "Modbus Poll Bytes Missing" Error

2. Quick Diagnostic Steps

| Step | Action | |------|--------| | 1 | Check communication settings: baud rate, parity, stop bits, slave ID | | 2 | Increase Response Timeout (e.g., from 100 ms to 1000 ms) | | 3 | Add Delay between polls (e.g., 50–200 ms) | | 4 | Monitor raw serial traffic using a serial sniffer or Modbus Poll’s “Display → Communication” | | 5 | Test with another master tool (e.g., ModScan, QModMaster) |

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2. Faulty Wiring or Loose Connections

RS485 requires a twisted-pair cable with proper termination. A loose ground or a missing termination resistor creates reflections, corrupting the frame and dropping bytes. modbus poll bytes missing error fixed

D. Software / Driver

• Update serial driver (especially for FTDI or CH340 chips)
• Close other applications accessing the COM port
• Reduce polling rate (add silent interval between requests)

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Step 4 – Change Modbus Poll "Frame Timing" (Advanced)

In Modbus Poll, open Display > Communication Traffic. Look at the actual response packets. If the last 2 bytes (CRC) are sometimes missing: Guide: Fixing "Modbus Poll Bytes Missing" Error 2

• Go to Setup > Read/Write Definition.
• Uncheck "Delay after poll" (set to 0).
• Check "Silent interval before poll" and set to 15 ms.

This forces Modbus Poll to wait 15 ms of bus silence before sending the next query, allowing the slave to finish its response completely. Update serial driver (especially for FTDI or CH340

Step 0 – Backup Your Modbus Poll Configuration

Save your .mbp project file. You will change multiple settings.