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Master your serial communication challenges with our advanced Serial Port Sniffer for Windows. This essential tool monitors data traffic between your applications and COM ports, allowing you to diagnose issues and streamline debugging processes. Perfect for developers and engineers alike, our sniffer offers an intuitive interface and powerful features to enhance your productivity.
The serial port sniffer allows studying the data exchange’s peculiarities of any Windows program. If you have developed the researched program, the serial/RS232 port sniffer turns into an RS232 debugger, which allows you to trace down and troubleshoot problems appearing in serial communications.
How can I sniff serial port communications using Advanced Serial Port Monitor?
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Launch our Serial Port Monitor.
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Select the «Spy» mode.
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Select the necessary RS232 port number from a drop-down menu.
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Start port monitoring by clicking the «Open» button _before_ another application starts using that port.
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Select an appropriate data view mode between ASCII and HEX.
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Monitor RS232 traffic in real-time, or start saving it using the «Write to file» button.
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Close the monitoring session by clicking the «Close» button.
Download a Free Trial Version
Serial Port Sniffer & Analyzer
Key Features of the Serial Port Sniffer
| Monitors Windows kernel-level I/O packets (output control codes, IOCTL) sent/received between serial port device drivers. | Yes |
| Interception of device control commands | Yes |
| Show info about port parameters used by another serial application (baud rate, number of data bits, etc.) | Yes |
| Monitoring activity of other software applications | Yes |
| Capturing serial port traffic | Yes |
| Virtual environment and virtual machines | Yes |
| Logging to a file that you can use for future analysis | Yes (Binary or Text) |
| Proprietary protocols, Custom protocols, Protocol analyzer | Limited |
| Advanced Features (ports autodetection, serial port name) | Yes |
| MODBUS RTU & ASCII monitoring | Yes |
| Advanced Filtering | The filtering capabilities in our sniffer allows you to filter out unnecessary kernel I/O requests |
| Advanced Data Filtering Capabilities | No |
| Convenient data visualizers | HEX, Text, ASCII symbols, and codes |
FAQ
Does your software use a driver?
Yes, our software solution has a particular device driver that our program attaches to an RS232 device’s driver. Our driver captures all communications and system requests with precise timestamps. You can get information about used baud rates and other communication parameters in most serial port software.
Is it compatible with Windows 10 and 64-bit operating systems?
Yes, our serial sniffer driver is compatible with the modern OS and has the necessary digital signatures.
Can your utility work with full-duplex?
It works by default because it inserts our driver in the middle of a serial device driver and another program. So, you can implement a bidirectional data sniffing interface.
What serial port types does your sniffer support?
Our serial software supports real and virtual COM ports (VCP) of various types, like RS232-USB (USB cables), RS232-LAN, Bluetooth, software-based Virtual COM port, etc. You do not need a special sniffer cable or an active RS232 sniffer cable. Still, you can optionally use it in the «Dual port» mode to monitor the serial connection between two external devices.
Download a Free Trial Version
Easily sniff traffic & capture data
Who can get benefits from a serial port sniffer:
- Serial protocol development by software system engineers.
- Industrial control equipment support teams can test industrial equipment and industrial automation systems.
- Hardware developers while creating new hardware solutions.
- DIY: try to send commands and watch responses from a connected device using USB UART dongles.
Eliminate RS232 cables
Using the serial port sniffer mode, you can monitor serial port activity without any cables and additional hardware.
Multiple COM ports at the same time
Start several instances of our COM port sniffer and monitor communication with your peripheral devices simultaneously. The program allows you to store the settings for each copy individually.
Easy-to-use
The RS232 monitoring tool does not require special knowledge, and students and professionals can use it to test/debug/view serial communication. You can use the RS232 monitor without any programming skills.
Free serial port sniffers on the market
Portmon monitors Windows kernel-level I/O packets sent/received between serial port device drivers. It didn’t update for some time and may not work on modern versions of Windows.
How can our serial software replace free Portmon?
Apart from Portmon, our software does not show low-level I/O requests, but decodes them to a human-readable form.
How can our software help decode serial communication protocol?
When studying serial communication protocols, you may want to repeat the same command sequence sent to serial equipment. You can quickly switch from the sniffer mode to the manual mode, repeat RS232 communications using our «Replay logs» plugin.
Download a Free Trial Version
The powerful alternative for free Portmon or other sniffers
See also
RS232 Analyzer from Advanced Serial Port Monitor
RS232 Monitor is a unique monitoring tool for communications via RS-232
Capture and analyze COM port traffic with our Windows RS232 serial port sniffer
Spying on a serial port or RS232 port using our Serial Port Monitor software
RS232 terminal
UART monitoring using our Serial Port Monitor
COM port scanner
5 common errors with COM port operations in Windows
How to find application COM port and list all COM ports in Windows
HDD Serial Port Monitor
HDD Serial Port Monitor is another friendly COM port sniffer for Windows, which allows monitoring and recording data from RS-232, RS-422, and RS-485 interfaces. This handy solution will help you easily analyze serial port activity and detect any issues with serial data communications.
Serial Port Monitor freeware gives you the way to sniff several COM ports simultaneously, so you can see how your apps interact with several serial devices within one session.
This app is especially useful for those who develop serial software, device drivers or serial hardware. It is a convenient tool for testing, debugging, and optimizing RS232 products.
One of the key advantages of this solution is that you can use this software sniffer of RS232 ports for free, but with limitation.
Serial Monitor is a reliable solution which works with high data transfer rates and makes it possible to easily change the way the raw data is displayed. Even if the session is completed you can still save the monitored data for its further analysis. This RS232 serial communication software is friendly and flexible and definitely deserves your attention if you’re a serial app developer or tester.
2. EZ-Tap RS232 Pro RS232 sniffer
RS232 hardware sniffer produced by Stratus Engineering will help you resolve the latency and time-tagging issues commonly faced by users of traditional dual COM port sniffing tools.
The clear benefits you get with EZ-Tap RS232 Pro hardware:
- No need to rely on bulky and expansive RS232 sniffer cables;
- You can track down the activity of multiple serial interfaces at a time and redirect the monitoring data to a file;
- The app provides simple access to serial ports and logging of all the data sent and received;
- EZ-Tap RS232 Pro fully supports Windows 2000/XP/Vista/7/10 (x32 and x64);
- Together with the hardware Com Port Sniffer, you receive the device drivers, Mini-B USB cable and a dedicated EZ-View monitoring software.
This RS232 packet analyzer can monitor full and half duplex serial communications and stream data to a dedicated RS232CPM COM monitor application.As well as an active rs232 sniffer cable that monitors the DTE/DCE and RTS/CTS lines in addition and Tx/Rx lines. EZ-Tap RS232 Pro is equipped with a male DB9 connector on one end and a female DB9 connector on the other end. Thanks to this, it can be inserted between two COM-based devices that need to be sniffed.
To use this solution, you just need to connect it to a USB port of your PC with the help of a USB A to mini B cable, install its drivers as well as the supplied RS232CPM app and start sniffing.
A nice thing about the RS232 COM Tap is that it can also be used with any RS232 terminal app supporting virtual COM ports, for instance, Windows HyperTerminal.
Modbus Sniffer
Modbus is a master/slave serial communication protocol popular in the industrial environment mainly because it’s openly published and royalty-free. Originally It was used to connect various industrial electronic devices over RS-485 protocol, though many other versions are available now for RS-232, RS-422, and TCP/IP (Modbus TCP) protocols.
Modbus protocol has a broad scope of application, particularly Modbus ASCII and Modbus RTU versions. The second is used the most among all Modbus protocols. So, if you are in the process of developing software to communicate with some electronic devices through the Modbus RTU, you’re definitely going to need a high- grade Modbus RTU sniffer. It’s a specialized RS485 Protocol Analyzer that will help you to analyze data sent through the protocol. The same applies to the Modbus ASCII version, with the only difference that you’ll need another version of a port scanner software.
Modbus Sniffer by Electronic Team, Inc. allows you to not only monitor all the relevant data sent through Modbus ASCII and Modbus RTU protocols but also log it for future analysis. It has a user-friendly interface and displays data in different view modes. On top of that, this particular protocol analyzer provides an opportunity to filter collected data for more accurate analysis.
With this professional-grade Modbus sniffer software you’ll be able to:
- Establish a connection with any serial port and instantly get a full real-time view of all the information transferred through it, so you can straightaway fix all the emerging problems. Even if some other application is already using that port at the very same time, it won’t stop Modbus Sniffer to effectively carry out its task.
- Simultaneously monitor multiple serial ports and conveniently log all the gathered information into a single file by the first-in-first-out principle.
- Choose the modes to display captured data: table, line, dump or terminal. Use them in any combination and apply filters for a more accurate and comprehensive analysis.
- Check the serial device’s response to specific commands with an emulated transmission of data.
- Use the terminal mode to emulate data transmission from a monitored serial port to a device that is connected to it. This feature might be particularly useful during the Modbus communication test, given that it provides means to monitor any given device responds to certain commands or data.
Serial sniffer
Long story short — this project aims to provide an easy (or at least well documented) procedure of sniffing serial ports without using additional hardware. There are existing solutions to this problem but you would need to hit yourself pretty hard in your head to pay from $100 to $500 for any of them.
Table of content
- Concept
- Supported OS
- Windows
- Linux — planned, 2nd priority
- Mac OS — planned, 1st priority
- TODOs
- Credits
Concept
In order to fully capture traffic both ways we need to have one real COM port that we want to sniff and 2 virtual ones since serial port can be used only by one program at the same time. The idea is to sniff incomming traffic from real COM and pass it through to one of virtual ones and do the same thing in reverse (sniff from virtual COM and pass it to real one). Communication between VCOM1 and VCOM2 is handled internally at a driver level.
Flow diagram taken from SerialSniffer:
Supported OS:
| Platform | Support | Tested on |
|---|---|---|
| Windows | ✅ | Windows 11 / AMD 3900X |
| Linux | ❌ | Ubuntu 22.04 / VM on Win above |
| Mac OS | ❌ | macOS 14 (ARM) / Mac 14 Pro with M2 |
TODOs:
- Gather docs for windows specific solution — first PoC
- Create python app handling communication between 2 virtual ports (remove SerialSniffer dependency)
- Add support for Mac OS
- Add support for Linux
Credits
- SerialSniffer
- fjovine for creating SerialSniffer
- xiaolaba for fixing it
In this article, will will cover how to sniff serial port communication with the help of virtual COM ports.
Serial port sniffing is the process of intercepting the data being transmitted over a serial communication port. It can be useful for a variety of reasons, including troubleshooting, debugging, or reverse engineering. Serial ports are commonly used to connect devices such as modems, printers, and industrial control equipment to a computer.
⚠️ Please be aware that serial port sniffing should only be performed with proper authorization.
Physical COM port
First of all, you need to know the exact physical COM port number on your computer. Start by going to the Device Manager. Once there, expand Ports (COM & LPT). Keep the COM port assigned to the device by Windows, such as COM1, COM2, COM3, etc.
In this example, my physical port is COM5.
Let’s say I have a piece of software which is communicating with COM5 and I want to «sniff» that traffic. However, sniffing COM5 traffic directly is not possible. So we will create virtual ports.
Virtual COM ports
In order to sniff serial port communication, we need to create virtual COM ports.
A virtual COM port is a software-based interface that emulates a physical serial communication port on a computer. It allows software applications to communicate with hardware devices that use a serial interface without the need for a physical serial port. A virtual COM port is assigned a COM port number, just like a physical serial port. Software applications can communicate with the virtual COM port using standard serial communication protocols such as RS-232, RS-485, or TTL.
Null-modem emulator (com0com) is an open source kernel-mode virtual serial port driver for Windows, available freely under GPL license.
- Download and install com0com v.3.0.0 setup 32+64-bit signed.exe
- Use the Start menu shortcut: com0com > Setup
- Create virtual port pairs as seen in the screenshots below
- Click the «Apply» button
My physical port: COM5
My virtual port pairs: COM1-COM91 and COM2-COM92
You must use your own physical COM port number by checking from Device Manager.
You can change your virtual port numbers as you wish, or stick to the numbers I randomly selected. Ensure that the ports you selected are available and not in use.
Route serial port communication
Now that our virtual ports are active, we can route physical port communication as we want. We will use hub4com for directing COM port traffic.
Before routing the traffic, our physical port (COM5) must be available. So, we need to close the application which uses our physical COM port.
- Download hub4com.exe
- Open command prompt (cmd) and enter the command line parameters below
hub4com —baud=9600 —octs=off —route=All:All \\.\COM5 \\.\COM91 \\.\COM92
Press Enter
⭐ The hub4com command prompt must be running during sniffing.
Sniff serial port communication
Now that the physical port traffic is routed, we can now open the software which was using the physical port. But this time, it must use one of the virtual ports (COM1), instead of physical port (COM5).
We can now sniff serial port communication with the help of Vovsoft Serial Port Monitor. The sniffer software must use the other virtual port (COM2).
As a result, we can see all incoming and outgoing data (via COM1) in the sniffer program (using COM2). In addition, we can send data through the sniffer program, as if it were sent from the other program.