Consider increasing the (the delay between polls) to ease the burden on the slave device. Give the hardware a second or two to breathe between requests. Step 3: Analyze the Communication Traffic
When the network is idle, the data lines float, which can generate ghost bytes. Ensure your master device or converter has pull-up and pull-down biasing resistors enabled to keep the lines in a stable state.
Before diving deep, check:
The Tx (Transmit) counter increments normally, but the Rx (Receive) counter shows incomplete frames.
In Modbus Poll, navigate to Setup > Read/Write Definition . Locate the Response Timeout field. Increase this value from the default (typically 1000ms) to 2000ms or 3000ms . If you are using a slow wireless radio link or cellular gateway, you may need to raise this even higher. 3. Latency in USB-to-RS485 Converters modbus poll bytes missing error fixed
If your slave is set to 9600 Baud and your master is at 19200, the data will be scrambled, leading to missing bytes.
If the Slave device is a bit slow (perhaps it’s an old PLC or a complex sensor), it might start sending data, pause to process, and then finish. Modbus Poll might see that pause as the end of the message. Consider increasing the (the delay between polls) to
Modbus RTU (serial) and TCP (Ethernet) protocols rely on strict timing and packet structure.
To truly master Modbus diagnostics, you should be able to calculate and read a Modbus frame manually. Let's look at what a standard read request and response look like. Ensure your master device or converter has pull-up
If your parameters are correct but the error still happens intermittently, your timeout settings are likely the culprit. In Modbus Poll, navigate to > Connection Setup .
Our system consists of a master device that polls multiple slave devices using the Modbus protocol. The master device sends a request to the slave devices, and the slave devices respond with the requested data. The system uses a serial communication interface to transmit data between devices.