Complete Serial Port Testing Guide

Olga Weis Oct 30, 2024

There are many instances where the ability to troubleshoot problems in serial interfaces and devices can be important. Many industrial and commercial devices such as automation controllers, medical monitoring equipment, and scientific instruments make use of serial ports for communication. It can be quite challenging to identify the underlying issues, and we describe some common ones in our RS232 troubleshooting guide.

The most important item required for this type of problem resolution is a quality tool that can provide the information required to address the issue. Here’s where an excellent app like Serial Port Tester can save you time and trouble when tracking down serial communication problems.

This article discusses the features of this software solution and walks you through this very effective way of how to check serial port communication.

Contents:

RS232 Testing Software overview
How to test COM ports: step-by-step instructions
- ❑ Monitoring serial port activity
- ❑ Resending data to a COM port
- ❑ Compare monitoring sessions
Ways of implementing a loopback test
Conclusion

RS232 Testing Software overview

Serial Port Tester (Serial Port Monitor)is a versatile serial communication tool designed to display and capture data transmitted through system COM ports. Ideal for developers and testers of serial applications and devices, this software simplifies the analysis of port activity by automatically logging all interactions, eliminating the need for manual documentation.

Serial Port Tester is a powerful, user-friendly tool for analyzing RS232, RS422, RS485, and Modbus communications.

Serial Port Monitor

Log and analyze serial port activity

4.8 Rank based on 345+ users, Reviews(345)

Download 14-day fully-functional trial period

Key Features of Serial Port Tester

This application boasts a range of features that make it a standout choice for serial communication analysis. Its intuitive, user-friendly interface allows easy access to the software's powerful capabilities, including:

Multiple Data Viewing Modes: View data in four different formats, providing flexibility in analysis.
Built-in Terminal: Send data directly from the application using the integrated terminal.
Advanced Search and Filtering: Quickly locate and isolate specific data with comprehensive search and filtering tools.

Comprehensive Protocol Support
Serial Port Monitor supports a variety of serial communication protocols, including RS232, RS422, RS485, and Modbus. Users can easily export data to a file or copy it to the clipboard for further use.

Modbus RTU and ASCII Support
Modbus is one of the most widely implemented serial communication protocols, with Modbus RTU being the most common variant. If you're developing software that interfaces with electronic devices via Modbus RTU, Serial Port Monitor offers an ideal solution for monitoring and analyzing Modbus RTU and Modbus ASCII data packages. This tool provides an intuitive way to visualize Modbus data, making it easier to understand and troubleshoot communication issues.

How to test COM ports: step-by-step instructions

For this demonstration, we will use Electronic Team’s Serial Port Tester as our COM port testing application. We will walk through a few typical use cases for the software.

First case: monitoring serial port activity

Use this procedure to monitor your system's serial port activity.

1

Download and install the program. Launch it and proceed to the next step to start a new monitoring session.

2

From the main menu choose "Session > New session", use the 'Ctrl + N' keyboard shortcut or click "New" on the toolbar.

3

The "New monitoring session" window will be displayed.

You can now select the viewing mode which will be used to display the monitored serial data. The four choices are:

• Line: displays IRP details in lines of plain text;

• Dump: two-way serial data displayed in hexadecimal and string formats;

• Terminal: presents the data as ASCII characters;

• Table: recorded IRPs are displayed in a table.

"Select all" or "Select none" are other viewing options

4

Select "Start monitoring now" to start monitoring right away and enable the "New window" option if that is where you want to conduct this session.

5

Choose the events you want to monitor in the "Capture options" menu. You can select create/close, read/write, or device control.

6

Click "Start monitoring" to begin the monitoring session.

If you want to save the session, select "Session -> Save session/Save session As" from the app's main menu.

Second case: Resending data to a COM port

Reproducing the data flow between a serial interface and a serial application or device can be instrumental in testing and resolving problems. Using Serial Port Tester, you can repeatedly send identical serial data streams to observe the behavior of an app or device.

Follow these steps to send data to a serial port:

1

Open a current monitoring session or start a new one.

2

“Select Session > Reproduce” and configure the parameters that will be used in the transmission.

Use port - This parameter designates the COM port that will receive the reproduced data stream.

Send requests to this port - This option is enabled when you are sending data to a serial interface as if it is coming from a serial application.

Respond as a device - Use this option when you are sending data to a COM port on behalf of a serial device.

Preserve time intervals - Data packets will be sent with predetermined time intervals when this option is set.

Custom IO timeout - Define the Read/Write timeout parameters you will use for the session.

3

Click ”Start”

Third case: Compare monitoring sessions

Comparing two saved monitoring sessions can provide valuable information regarding your serial communication.

After you have saved the monitoring session using serial port test software you can compare it with another session to see the differences.

To achieve this, just do the following:

1

Start or open a monitoring session.

2

On the main menu, choose “Session > Compare Sessions”.

3

Choose the monitoring file that will be used for the comparison.

4

The sessions will be displayed side-by-side, making it easier for you to analyze the differences in the sessions.

Ways of implemented a loopback test

What is loopback testing

A loopback test involves sending and receiving data from the same COM port. A signal is initiated from a device and returned to it after traversing part or all of a network.

What information does the loopback test provide?

The loopback test is providing information about:

problems in a network of serial devices;
ways to determine if a device is operating properly.

It’s an important method for troubleshooting serial communication problems and make sure that the COM port works correctly.

It often employed to address issues with RS232, RS422, and RS485 communications. You can emulate a communication circuit with a loopback test and eliminate the need for extra equipment to track down problems. Some modification of the port’s pins needs to be done in order to allow two-way communication on the same interface.

How to do a loopback test

A simple loopback test of an RS-232 interface requires connecting the transmit (TXD) pin to the receive (RXD) pin. The differential pairs of the RS-422 and RS-485 protocols demand the connection of the TXD+ pin to the RXD+ and the TXD- to the RXD-.

Hardware flow control can be incorporated into more advanced loopback tests by making additional pin connections. Similarly to the transmit and receive pins, in an RS-232 port you connect the CTS and RTS pins to the DTR and DSR pins. For RS-422 and RS-485 interfaces, you connect the CTS+ with the RTS+ and CTS- with RTS-.

Below you can see the pinout diagram of a common serial connector, DE-9:

For a simple loopback test (marked red in Fig. 2,3 below), you connect:

pins 2 and 3 for RS-232;
pins 4 to 8 and 5 to 9 for RS-422/485.

For a loopback test with a hardware flow control (marked blue in Fig. 2,3), you connect:

pins 4 to 6 (DTR/DSR hardware flow control) and 7 to 8 (RTS/CTS hardware flow control) for RS-232;
pins 2 to 3 and 6 to 7 for RS-422/485. Both connections are required to address the differential connections.

Pin numbers are often engraved on the connector casing. This is how pins are identified in the DE9 connector of the RS-232 serial port:

Loopback Test in HyperTerminal

HyperTerminal permits your computer to act as a terminal to remotely connect with other systems. It employs telnet or a standard RS-232 serial bus to connect with remote devices.

Since HyperTerminal makes use of serial ports for data transfer, it can be used for loopback testing.

This is how it’s done:

1

Create a new connection in HyperTerminal and name it. Select the icon for your connection.

2

Identify the communications port you will use for the test.

3

Select the type of flow control that will be used for the test. Our options are Xon/Xoff, hardware, and none. If you select the software flow control of Xon/Xoff, only the TXD and RXD pins need to be connected.

4

Type a message on your keyboard. Data received from the device will be displayed in HyperTerminal.

While performing loopback tests with HyperTerminal is convenient, there are more efficient ways to test RS-232 ports.

There are limitations to this serial loopback test which inhibit your ability to debug issues that arise in hour serial communication. Windows 7 and 10 only support the paid and private version of HyperTerminal which may impact your decision to use it as your testing platform.

Conclusion

Many methods and strategies can be used in an effort to diagnose and resolve serial communication problems. We have looked at some of the most popular alternatives. We believe Electronic Team’s Serial Port Tester offers the best solution based on its versatility and powerful suite of features. It provides an alternative to HyperTerminal and can be used as Modbus testing software. It is a valuable tool for individuals involved in the development and testing of serial devices and applications.

#1 at Serial Port Software

Serial Port Monitor

Log and analyze serial port activity

4.8 rank based on 345+ reviews

Get a download link for your desktop
Submit your email address to get a link for quick download on your desktop and get started!

or

Download

Purchase Now

Information

Requirements

Requirements: Windows (32-bit and 64-bit): Vista/7/8/10/11, Windows Server 2008/2012/2016/2019/2022, Windows on ARM

Latest version

Latest version: v9.5.600, Released 8 Mar, 2025 Release notes