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How To: Set Up Communication Parameters

Before making a connection to a Modbus device there are a few parameters that must be setup. To do this, the Tester provides the Communication Setup form. This form can be opened by choosing Communication->Setup menu item or by clicking the Communication Setup Toolbar button .

If the Communication Setup form is opened when an active connection to the device exists, the form is displayed in a read-only mode. All controls on the form are disabled but will show the current values of settings. This means that connection parameters can be changed only in a disconnected state.
A: Timeout

This is the amount of time the Tester will wait to get a response from the device after it has sent a Modbus request to it. If no response is received within this time, a "timeout" is considered to have occurred and the transaction is aborted. The value specified is in millisecond.

B: Comm. Mode

Use this option to select Modbus RTU or Modbus TCP mode.

C: IP Address

The IP address of the device to connect to.

D: Port No.

The TCP port number on which the device services Modbus TCP connection requests. Port 502 is the Modbus standard port. There are only a handful devices which use a non-standard port number. If so, the port number used will be provided in the device's User Manual.

E: Serial Port Settings

Use these parameters to set serial port settings. They are only available if connection type is “Modbus RTU”.

F: Reconnect on startup

Enabling this feature will cause the Tester to attempt connection to the device on startup. The connection will be made as per the last configured settings.

G: Autoreconnect on disconnection

Enabling this feature will cause the Tester to attempt reconnection whenever an existing connection to the device is dropped due to network or device problems. Auto reconnection is not made if the user manually disconnects using the Disconnect menu item or the toolbar button. The reconnection attempts will continue in the background at a periodicity set by the "Reconnect Interval" field (see below) until the connection is successful or the user disables this feature.

This feature is extremely useful when doing unmanned long duration testing on devices. If during such a test the connection is dropped, say, due to a device reset, the Tester will automatically reconnect to the device when the device reboots thus maintaining the continuity of the test. In the absence of this feature the test would be aborted when a connection drops. The occurence of such reconnection events is logged into the event log file which can be analysed at the end of the test to detect if there was a communication break during the test.
F: Reconnect Interval

This field is related to the "Autoreconnect on disconnection" field and is used to specify how often the Tester will attempt to reconnect to the device if the last attempt was unsuccessful.

Related Information

Topic link How To: Configure Modbus Protocol Tester for Modbus RTU communication
Topic link How To: Configure Modbus Protocol Tester for Modbus TCP communication
Topic link How To: Connect to a Modbus a device
Topic link How To: Disconnect from a Modbus a device
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