RS232 sniffer. How to sniff com port communication?

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When working with systems and devices that use the RS232 communication, an RS232 Sniffer can be very useful. A serial port sniffer provides the ability to monitor full-duplex communication passively, meaning it does not impact system performance. The information returned by a COM port sniffer can be used to diagnose and troubleshoot issues in serial communication and allow you to verify that your devices are capable of high-quality serial data transfer.

You may have some questions regarding the use of a serial sniffer that need to be resolved before you implement the solution. Here is a brief overview of serial sniffing:

  1. What are the benefits of an RS232 sniffer?
  2. How to sniff a serial port?

What are the benefits of an RS232 sniffer?


  • An RS232 sniffer furnishes a monitoring solution for serial port communications monitoring. One of its components is usually a serial protocol analyzer that performs monitoring to diagnose and resolve problems with COM ports.
  • Serial sniffer software is designed to enable users to display the flow of data transmission and save it to a file for later analysis.
  • Our RS232 port sniffer can be used without the need of any programming skills. Users with general computing knowledge can easily access, monitor and analyze the serial communication between a COM port and any connected devices or applications.

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Serial Port Sniffer is a professional software tool that lets you track communications of any serial program with a COM-enabled device in your system.
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How to sniff a serial port?


1. Download, install and launch Serial Port Sniffer.

2. Choose “Session >>> New session” from the main menu. You can also use the keyboard shortcut “CTRL+N” or click “New” on the main toolbar.

New session

3.The “New monitoring session” window will open.

New monitoring session

Make your selection of the visualizers that will be used to display data during the monitoring session. The choices are:

  • Terminal view presents the captured data as ASCII characters in a text console.
  • Line view displays detailed information about the requests that are sent on a specific serial line.
  • Table view presents a table of the recorded IRPs.
  • Dump view displays all data received and sent on a particular serial line.
  • Modbus view displays received and sent Modbus data in both the RTU and ASCII formats.

Use the checkboxes designated as “Start monitoring now” and “Start in new window” to control the initiation of your new monitoring session.

Capture options: select the options you want to be monitored during the session from these choices: Create/Close,

Read/Write, and Device Control.

After setting the options begin monitoring in the new session by clicking the “Start monitoring” button.

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4. A new monitoring window will be opened using the visualizers you previously selected.

The process of monitoring

In the Status bar tune the settings you need.

COM Port status bar
  • nBaudRate : Defines serial port BaudRate. Possible values are: 110, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 38400, 56000, 57600, 115200, 128000 and 256000. By default, 110 value is taken.
  • nDataLength : Defines data lengths in a packet. Possible values are: 5, 6, 7 and 8. The default value is 7 bits.
  • cParity : Defines parity in one of the following values: (E)ven, (O)dd, (M)ark, (S)pace, or (N)one. By default (N)one is taken.
  • nStopBits : Defines a number of stop bits. Possible values are: “1”, “1,5” and “2”. The default value is “1”.
  • cHandflow : Defines flow control value. Possible values are: Hardware (P), Xon/Xoff (X) and None. The default value is None.

Serial/modem control lines state:

  • RTS : Request to Send line indicator
  • CTS : Clear to Send line indicator
  • DSR : Data Send Ready line indicator
  • DCD : Data Carrier Detect line indicator
  • DTR : Data Terminal Ready line indicator
  • RI : Ring line indicator

  • Serial Port Sniffer displays line levels graphically via colored circles. A green circle indicates a high line level with a red circle standing for a low level. An undetermined state is specified by a gray circle.

    5. Save a session by choosing “Session >>> Save session/Save session As” from the main menu. You can also use the CTRL+S keyboard shortcut or click “Save” on the main toolbar.

    Save testing session

    6. Select a file name when prompted by the application. You can make use of this file to reload it for later analysis or to continue the monitoring session.

    As you can see, the COM Port Sniffer for Windows can be instrumental in solving serial communication problems in many different industries. The tool can save time and money for developers of serial applications and devices.

    It can be challenging to implement an RS232 sniffer in the absence of a quality tool. Luckily, Eltima Software has you covered with a comprehensive and intuitive serial port sniffer tool that will effectively address your serial communication issues.

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