Device Connectivity

If you see a "Device not responding" message, this means that the driver is polling the device for data but is not receiving a recognizable response. This is classified as a communication problem.

If you suspect a communication issue to be the root of the problem here are the most common causes of communication errors.

1. Cables - The cable used between the PC and the device is always the first place to start. The only sure way to confirm the cable is to ensure that you are able to use this cable with other software such as the device configuration or programming package. If you confirm that the cable works with your programming package the most likely cause of the problem will be flow control settings. You may want to try setting the KEPServerEX channel configuration to a Flow Control of RTS Always or RTS,DTR. This is a common solution. Each KEPServerEX communications driver includes a specific help file with connection information and cable diagrams. Driver help can be accessed from the KEPServerEX Help menu or by going to the desktop start menu, then Programs folder, and then KEPServerEX folder. When using RS-485 or RS-422, check the Kepware web site for converters that we recommend. RS-485 and RS-422 converters are a common source of communications issues. If you are using KEPServerEX Modem capability for dial up modems, be sure to thoroughly read the Modem section of the KEPServerEX help file.

2. Channel Communication Settings - Do the channel settings for baud rate, parity, and number of data bits match the current parameters of the PLC or device? A quick test is to use the ladder-programming package of the PLC to confirm these settings. The full time online nature of KEPServerEX allows the communication settings to be adjusted while KEPServerEX has active client connections, so troubleshooting adjustments can be made quickly and easily. Simply invoke the properties tab on the channel in question in KEPServerEX and make the adjustments as needed.

3. Device ID - The Device ID set in the KEPServerEX project must match the communication ID of the PLC or device. Check the specific driver help file for unique device settings. Like the Channel properties of baud rate and parity, users can change the Device ID on the fly. Simply invoke the properties dialog for the given device in KEPServerEX and change the device ID as needed.

For Serial drivers: Most serial devices have a default ID of 1, but you must check the current ID of the device. You should be able to check this using the ladder programming package of the PLC. Also, make sure that the IDs in the device and KEPServerEX are in the same Decimal, HEX, or Octal format. The most common format is Decimal. Device IDs can also be adjusted while KEPServerEX has active clients.

For Ethernet drivers: Verify that you can ping the PLC's device IP from a Windows command prompt. If you cannot successfully Ping the device, the KEPServerEX Ethernet driver in use will not be able to communicate with the device.

For Modbus Plus(uses Modicon SA85 card): Verify devices on the Modbus Plus network with the Modbus Plus Network Browser Utility that installs in the KEPServerEX|Utilities folder of the desktop start menu.

4. Comm Port - Is the serial communication port (comm port) of the PC valid and not currently being used by another application or device? Are you certain that the comm port works? Use some other software package to verify that the comm port is functioning properly. If extra comm ports have been added to the PC, there could be an issue with IRQ conflicts. If the comm port is not working, the server will post an error message to the Event window. Check the "Error Descriptions" section of the appropriate driver help file for info on comm port error messages.

KEPServerEX does offer some unique built-in diagnostic tools that can make trouble shooting these types of issues a little easier. To enable the diagnostics invoke the properties dialog on your channel name in KEPServerEX. Once the properties of the channel have been exposed click on the "General" Tab. You can enable the Diagnostics as shown here:

Once the diagnostic features have been enabled invoke the diagnostic view by right clicking on the channel name and selecting Diagnostics, the result is the display of the diagnostic window as shown here:

As you can see the diagnostic window provides a protocol view as well as statistics on the number of read and writes that are occurring and the number that have failed. One of the most important aspects of the diagnostic window is the protocol view. If you display the diagnostic window first then invoke the channel properties dialog, you will be able to make changes to baud rate, parity, or stop bits and see the effect that has on the success or failure of the communications stream. This can be a powerful tool for helping you debug your communications issue. We almost go so far as to say it makes troubleshooting fun. For more information on the diagnostic window consult the KEPServerEX main help section "Diagnostics".

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