TCP Server

Starting and Stopping the TCP server

TCP stopped TCP started
If possible, the TCP server is started automatically upon application start. The server can be stopped and started at any time via the Start/Stop button in the RTU tab. The server connection status is indicated by the colour of the indicator above the port number.
A red indicator signifies Offline (Disconnected), a green indicator signifies the server is listening on the port number shown below the indicator.

TCP Server Bonjour

The Modbus server can be located via Bonjour services. While the server is listening on the configured port it can be located via Bonjour as a local service under the name _modbus._tcp
Bonjour browser

Monitoring client connections

Client connections to the TCP sever are displayed in the format of [ClientIPaddress:ClientPortNumber] and will be in blue colour while the connection is maintained.
TCP connected
After the client connection is closed the connection display will remain for a few seconds but in gray font colour. This feature allows the observer to identify clients which only connect for a very brief period of time.
TCP diconnected

Changing TCP port

The modbus server TCP port can be changed in the Preferences window (Apple Command-,) . Please read the following paragraph on the subject of port numbers.
Server prefs
Although the Modbus TCP port number can be changed, privileged ports (1-1023) require root access which is normally not available to OS X users. The standard (but unofficial) Modbus server port is 502 (privileged), we suggest using 1502 instead (not privileged).
However, some circumstances may demand port that the server listens on port 502. For example, if your client can not be configured to communicate to a server on port 1502 or any other port above 1023. In such circumstances, we recommend to open a terminal window and navigate to the folder where ModbusServer is installed (e.g. "cd /Applications/ModbusServer/Contents/MacOS/" on a SnowLeopard installation) and launch ModbusServer via the console using "sudo ./ModbusServer" (root password required).

!! Warning !!

Only use the sudo command if you really must as it could potentially compromise system security.

Using Modbus Server RTU Slave