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Kepware Knowledge Base: Solution

No Tag Data via TCP from Ethernet PLC/Device

Last Update: 11/12/2018

Channel Diagnostics can display basic information about a TCP connection to a native Ethernet PLC/device. The window may show one of three states: no TX or RX bytes, green (TX) text only, or both green (TX) and white (RX) text.

  • No TX or RX bytes means that the server cannot make a TCP socket connection to the device. This state will occur if no client attempts to access the device in question. If the Channel Diagnostics window's "Failed reads" or "Failed writes" are increasing within the amount of time specified in the Timing device property, then a client is connected. If the Channel Diagnostics window's "Failed reads" or "Failed writes" are not increasing, then there is no client connected. Before troubleshooting further, connect a client to the device in question. Suggestions for the "No TX or RX bytes" state are as follows:
    • Can you ping the device? If not, the server will not be able to connect. Verify that the PC and device are in the same IP subnet or that there is a gateway that can forward packets between the two subnets.
    • Are all the device's available connections in use?
    • Is a firewall blocking access to the TCP port that the driver is attempting to use?
    • Does the device require ladder logic or some other configuration to accept TCP connections? For more information, refer to the driver's product manual.
      Note: This state normally does not apply to UDP. Since UDP is connectionless, the server can transmit a UDP message even if there is no device to receive it.
  • Green (TX) text only means that the server can open a TCP socket to the device, but the device will not send anything back. To verify that the driver settings and PLC/device are set properly, refer to the driver's product manual for more information.
    Note: Some devices may support multiple Ethernet protocols using a different TCP port for each protocol. Make sure that the driver is set to connect to the appropriate port. The driver's default port usually will work.
  • Both green (TX) and white (RX) text means that the device can send messages back, but there is still something preventing access to the tags. Look in the server's Event Log for any error codes that the device might be returning. Then, verify that the driver settings and PLC/device are set properly by referring to the driver's product manual for more information.

See Also: Channel Diagnostics Guide

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