Any traffic received will be shown in the traffic window (top right) marked with an RX. If a received message is detected as a valid modbus request, a reply will be sent back and this will be shown in the traffic window marked with a TX.

You can click on any message in the traffic window to see a breakdown of what it means (bottom right). WinModbus will attempt to parse any message as a valid Modbus message but will display an appropriate error message if this is not successful.

WinModbus will only reply to a modbus request that matches a corresponding Function Range. Function Ranges are shown top left and they each specify a modbus function code and a range of addresses. Supported modbus functions are : 1, 2, 3, 4, 5, 6, 15, 16, 65, 66, 67, 68 and some function ranges are added by default to answer all of these.

By default, WinModbus will reply to all value requests with 0. To specify some valid data, you can create data items in the Address map (bottom left).