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How to Test Serial Applications

Olga Weis Olga Weis Nov 2, 2021

While developing serial apps, programmers may face some difficulties related to program testing. In some cases, it's not possible to modify the hardware device.

If your PC lacks serial interfaces, you may create virtual COM ports and use them as emulators of physical serial ports. In this article, we'll tell you about the simplest way to test serial applications with the help of a virtual serial port.

How serial port emulation works

Serial port emulation software can create virtual serial ports that emulate physical serial interfaces. These virtual COM ports can be connected using a virtual null-modem cable. The ports can then use communication software to exchange information between serial applications or devices as if they were hardware ports connected by a physical cable.

After being established by the software, virtual ports are indistinguishable from physical interfaces and will show up on your computer in the same way as a hardware device.

A connection between two serial applications is established when the apps open the virtual serial ports. At that point, serial data can be transmitted back and forth over the virtual ports. The two-way communication between the ports makes data sent to one immediately available on the other end of the connection.

Now let's see how to install a pair of virtual serial interfaces

  1. Download Virtual Serial Port Driver and install it on your computer.

  2. Start the program and open the "Pair" window. There you'll see the 'Add pair' option. Now, you can either select the virtual serial ports from the dropdown list or specify them manually. Pair window
  3. What is especially convenient is that you can assign any custom names to the ports you create with Virtual Serial Port Driver (except for those port names already used in your system). Just make sure that the apps that will work with these COM ports support the port names you've chosen.

  4. Click "Create" and that's it. The number of virtual COM port pairs you can create with the software is not limited.

Please keep in mind that if you're going to use the newly-created virtual ports with C# Windows application, you need to name them starting with COM. It's very important as the .NET Framework uses the System.IO.Ports to access the COM ports. To establish a connection we need to use a function named as serialPort1.Open() but it can only open a port which name starts with COM.

5 testing scenarios

Now let’s take a look at several scenarios that can benefit through the use of virtual serial ports.

  1. Testing and debugging serial applications is facilitated by using virtual serial interfaces. If you are developing new software or tracking down issues with installed serial solutions, virtual ports give you more flexibility than physical interfaces. One of their benefits is the ability to multi-thread data with a pair of virtual serial ports. scenario 1
  2. Firmware developers or technicians working on serial device drivers can use virtual ports for testing and debugging. This lets team members use any network-connected machine for serial testing even if it lacks physical COM ports. scenario 2
  3. Virtual serial ports allow users to work with remotely located applications and devices when no physical connection can be established. The endpoints just need to be attached to the same network. scenario 3
  4. Virtual COM interfaces can be used by applications designed to cache, log, and translate network data flow. They allow technical teams to access serial data transmission without physical connectivity to the devices and programs. scenario 4
  5. Virtual loopback serial ports can be established and added to bundles. A loopback can be very helpful when attempting to test how a specific port is handling data transfer. With a loopback, line parameters like baud rate will not impact data transmission. You will immediately be able to determine if information is flowing through the connection with no data loss.

How to test a serial port with HyperTerminal

One of the possible workarounds is using a null-modem cable, which allows connecting one program, e.g. HyperTerminal, to another. With this type of connection, you can not only link two computers together but also provide communication between two apps installed on the same PC. For this to be accomplished, you need to have at least two COM ports available in your system.

Once your virtual COM interfaces have been properly set up, you can start testing. As an example, we’ll consider testing COM ports with Windows HyperTerminal.

To launch a new HyperTerminal instance, head to Windows Start Menu > Programs > Accessories > Communication > HyperTerminal.

Say, you have a pair of virtual ports named COM3 and COM4. Here’s how to use hyperterminal:

  1. First,create a connection to COM3 port.
  2. After that, open the File Menu and select 'New Connection'. Enter a name, e.g. Test_COM3, choose the icon, and hit OK.
  3. Now, find COM3 in the dropdown list and press OK. Make sure the properties are kept default and press OK.
  4. Next step is creating a connection to the other port - COM4.
  5. To do this, open the File Menu > New Connection. Enter a name, say Test_COM4, choose the icon, and press OK. Choose COM4 from the dropdown list and hit OK. Keep the properties default and press the 'OK' button.

Starting from this moment, you can easily use HyperTerminal to test serial ports. Just type the required text in the white text area of COM3 and the written data will be transmitted via a virtual null modem cable and displayed on the screen of COM4.

As long as HyperTerminal supports data transfer via COM ports, you can use this program to perform a loopback test. If you feel the need for HyperTerminal replacement with a more advanced solution, HyperTerminal Alternative guide will help you.

Test serial port via Advanced Serial Port Terminal

Serial Port Terminal is a high quality serial terminal emulation solution. Its advanced features set it apart from competitive products with advantages such as the ability to simultaneously monitor multiple serial ports and the variety of formats that are available for viewing data transmission. The developers at Eltima Software fully support the tool and provide regular updates to ensure the application continues to deliver excellent results.

Serial Port Terminal

Here is a detailed guide that quickly gets you up and running with Advanced Serial Port Terminal. We will pass over a discussion of customization settings for the time being.

  1. After the program is started, you will want to establish a new connection to a serial interface. Choose the “File” >>> “New session” menu option which will bring up the “New session” dialog window.

  2. The “New session” dialog window is where you will define connection parameters such as the number of the serial port as well as its baud rate, stop bits, and parity settings. They need to be identical to the connection settings of the serial port that will be accessed remotely.

  3. Click the “Open” button to initiate the newly created session.

  4. After communication is established, the serial port needs to be opened using one of these three options.

    • ❒ Select “File”>>> “Open port” from the application's main menu.
    • ❒ Click the “Open port” button located on the toolbar.
    • ❒ Use the “Alt” + “O” keyboard shortcut.

  5. You need at least one unoccupied serial port in order to open it for use with the app. This means no other program can be using the interface when the connection is established.

  6. Once the port is opened, the connection can be used to send data in text, binary, octal, decimal or hexadecimal format. You can send binary or text files as well as monitor the behavior of the serial interface.
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