Wireshark Serial Modbus Communications

Serial Port Monitor (SPM) is a powerful Modbus sniffer tool serving as an optimal solution for analyzing data transferred within Modbus communications. Thanks to SPM’s outstanding functionality, you can easily detect and resolve any problem you may face when providing Modbus testing and debugging. The distinctive advantage of the software is its ability to display and log all the data transmitted through COM ports available in your system.

With the advanced search and filter options, offered by this efficient Modbus sniffer software, only relevant serial data will be shown to you. Another great SPM’s feature is a built-in terminal used for executing text commands. Serial Port Monitor is an easy-to-use app that supports different formats for exporting data and provides you with numerous significant options.

Serial Port Monitor can be purchased as a Standard, Professional or Company Edition. The moment SPM connects to the required COM port, it starts analyzing serial data transferred through it. By monitoring serial ports in real time, you can track down emerging issues and react immediately. Even when a COM port is used by another application, you’ll still have no problem connecting to it with the software.

Modbus TCP/IP Problem detectable with WireShark? Of the Modbus communication (not via wireshark). Port for Modbus TCP? Does Wireshark recognise serial over. Oct 14, 2014  This shows how to configure Wireshark to view Modbus RTU packets captured using the USB Serial Capture Window.

All data, collected by SPM, can be viewed in different modes, which greatly simplifies the process of data comparison and evaluation. In addition, Serial Port Monitor can work as Modbus RTU sniffer.

Hello, Here is my problem. In an industrial automation environment we have one Modbus Master system and serveral Modbus slave's (13 x PLC's/PC devices). Modbus communication is working, but frequently (twice per hour) we lose the connection to one of the devices (everytime a different device). This takes a couple of seconds (10-20 sec) and then the communication starts again. We can see that the frequency of missing the connection is related to the number of slaves active on the network.

When we have less slaves on the network it still happens but less frequent. In our Modbus Master system there is no good log available to see what is happening. I used Wireshark to capture the datatrafic between the master and the slaves. I've got a situation captured, but to be honest i really don't know what i am looking at in Wireshark.

Hopefully someone can explain to me what the Wireshark log can tell me. Thanks, Niels Hereby a link to the file on cloudshark: Problem is between 141.81.0.10 and 141.81.0.46 on time: 03 min, 46 sec until 04 min, 06 sec Hopefully this will help to find my problem???? Thanks Screenshot of Configuration in Master System (Wonderware AcherstrA). The Modbus devices are Elau PLC controllers. Also we communicate with an Xray machine wich has a dedicated PC based controller. Thanks to everyone for cooperative thinking and helping.

Might be on to something here. In the first capture, if you filter by the rtu address (ip.addr == 141.81.0.46) and look at the frames preceding the connection close, i.e. 29986 onwards, you can see a sequence of Read Input Register requests. Looking at the Modbus/TCP headers you can see the 'Transaction Identifier' that allows the master to match up responses to queries and have multiple queries in flight. Standard Modbus doesn't have this as it's a strict request/response protocol, but the TCP variant does. So the query in frame 29986 has TI's 4. The response (30004) has the responses to those TI's.

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The next query (30006) has TI's 28535 & 6. The next response (30067) has the responses to those TI's.

The next query (30069) has TI's 0. The next response (30107) only has TI's 28537 & 8 so TI 28539 & 40 are still outstanding (in flight). The master then sends a query (30109) with TI 28541 and then another query (30126) with TI 4. Note that the latter two are actually coil writes so I'm speculating that the master pushed the writes out immediately (as we all like output ops to happen quickly) so now we have TI's 4 all in-flight. The rtu responds (30149) with TI 25839 & 40, so TI's 25841-44 are still in-flight.

Now we have the near 10 second gap until the rtu sends the tcp keep-alive (36817) and very quickly after that the master closes the connection. I think that the number of TI's in-flight (4) cause the master to not send any more queries until the rtu responds, and as this doesn't happen in 10 seconds or so (a master timeout?) the master recycles the connection. I would further speculate that if the master has a write request, it may exceed the 'normal' number of in-flight requests. You need to check the permitted number of in-flight requests for the rtu, and (if possible) configure the master to not exceed that.