How to Read Serial Port Data: A Comprehensive Guide for Windows

Reading serial port data is important for individuals in multiple fields. Hardware and software developers, engineers, and hobbyists may need to perform COM port data analysis on equipment supporting serial protocols like RS232 or RS485. This guide discusses using specialized serial communication tools to read the data, optimize data transfer rates, and resolve problems to support more reliable communication.

Contents

1. What is Serial Communication?
2. How to read data from a serial port?
3. Main features of Serial Port Reader for Windows.
   3.1 How to capture serial port data on Windows with COM Port Reader?
   3.2 Advanced Troubleshooting and Optimization
4. The RS232 Connection and Signals
   • • DTE and DCE
   • • DB-9 to DB-25 Conversion
   • • RS-232 Connections
   • • RS-232 Signals
5. Applications that Rely on Reading Serial Data

What is Serial Communication?

Serial communication involves sending data over a single wire one bit at a time. It is commonly used in embedded systems, legacy peripheral devices, and industrial equipment. The RS232 protocol is considered a standard in serial communication. Recently, USB-to-serial adapters have become increasingly popular in modern computing systems.

How to read data from a serial port?

1. Set up the Serial Connection
   
   
   • ■ Verify the serial device is connected to the computer using the machine’s serial port or a USB-to-serial adapter. You can obtain the COM port number using the machine’s device manager.
   • ■ Configure the communication parameters to match those of the serial device. Effective communication requires matching parameters such as baud rate, parity, and flow control.
2. Select a serial port reader tool. Specialized software is required to monitor and analyze serial port data. Serial Port Monitor is an efficient tool for this purpose.


3. Start the Monitoring Session
   
   
   • ■ Start a new monitoring session after installing and configuring Serial Port Monitor. The software will capture data as it passes through the COM port so you can monitor communication between the connected device and the computer.
4. Real-Time RS232 Data Reading
   
   
   • ■ The monitoring session collects data in real-time as it is transferred through the serial port and displays it in your chosen format. Data can be exported for offline analysis as CSV, HTML, or TXT files.
5. Additional Serial Port Monitoring Tools
   
   
   • ■ pySerial offers Python users a library of procedures for reading serial data. Check out this pySerial tutorial video.
   • ■ PuTTY is a free solution that allows you to read serial port data. Here’s a video tutorial discussing using PuTTY for COM port monitoring.

Main features of Serial Port Reader for Windows:

• Reading COM port activity

This software utility allows you to read RS232 data from a designated port and monitor it even if another application had already opened it. Captured serial data can be displayed in various formats, and the opportunity of real-time monitoring is a great feature for problem resolution.

The received data can be saved to a file of your choice or copied to the clipboard. The tool displays and files input/output control codes (IOCTLs) along with their complete parameters. Sessions can be saved by Com Port Reader and can be reloaded if required.

• Working with multiple ports in one session

Multiple serial ports can be read simultaneously by this software tool. This feature is very useful when comparing data collected from different COM ports that are interacting with the same application within monitoring session. In this case, all data is received and stored in a single log file on a first-in-first-out basis.

• Multiple views for sniffed data

Serial Port Reader allows you to choose the way that collected data is displayed on your computer. Four different view are available: table, line, dump, or terminal. You have the option of monitoring all view modes at the same time.

• Emulating serial communication

An option in terminal mode allows simulated data transmission from a serial application to a monitored COM port. Various data formats, such as string, binary, octal, decimal, hexadecimal, or mixed, can be used to test the COM port or its attached device’s reactions.

• Capturing Modbus data

COM Port Reader’s powerful filters enable you to read serial data transmitted over Modbus RTU and Modbus ASCII. The utility is fully compatible with these protocols, as well as those employed in RS-232, RS-485, and RS-422 interfaces

• Repetitive data exchange

Sending the same command from a serial app to a monitored serial port multiple times can give a clearer picture of the port’s behavior. This serial port utility simplifies that task with a playback feature that can display differences between sessions automatically.

Give your session a meaningful name so you can return to it for later analysis

Advanced Troubleshooting and Optimization

Troubleshooting common serial communication issues

• Data corruption may result from bad cables or dissimilar baud rates.
• Unresponsive devices are often the result of incorrect COM port and parameter settings. Some devices may require flow control for smooth data transfer.

Error Detection and Handling

Using error detection techniques such as conducting a Cyclic Redundancy Check (CRC) or checking parity bits can identify transmission errors often associated with long cables or noisy operational environments.

Optimizing baud rate

Choosing the right baud rate is crucial for consistent and reliable communication. A high baud rate may deliver data too quickly for a device to handle effectively, resulting in data corruption or loss. Serial Port Monitor lets you try different baud rates to optimize data transfer with your serial device.

The RS232 Connection and Signals

• DTE and DCE

DTE stands for Data Terminal Equipment. An example of a DTE is a computer. DCE stands for Data Communication Equipment. A modem is an excellent example of a DCE.

A DTE normally comes with a Male Connector, while a DCE comes with a Female Connector. This is not always the case. Here is a simple test to confirm device type. Using a voltmeter, measure Pin 3 and Pin 5 of a DB-9 Connector. DTE devices will indicate a voltage of -3V to -15V. DCE devices will have the voltage on Pin 2.

Note: The result for a DB-25 Connector is reversed (Please refer to DB-9 to DB-25 conversion table below).

• DB-9 to DB-25 Conversion

• RS-232 Connections

Straight-through cables are used to connect a DTE (e.g. computer) to a DCE (e.g. modem), with all signals in one side connected to the corresponding signals in the other side in a corresponding one-to-one basis. When connecting two DTE devices directly with no modem in between, a crossover, or null-modem cable is used. This type of cable cross transmits and receives data signals between the two sides. There is no standard and many variations on how the other control signals are wired. Below is an example of one of them:

• RS-232 Signals

The graphic above illustrates a typical RS-232 logic waveform (Data format: 1 Start bit, 8 Data bits, No Parity, 1 Stop bit). Data transmission begins with a Start bit, followed by the data bits (LSB sent first and MSB sent last), and ends with a "Stop" bit.

The voltage of Logic "1" (Mark) is between -3VDC to -15VDC, while the Logic "0" (Space) is between +3VDC to +15VDC.

RS-232 connects the Ground of 2 different devices together, which is the so-called "Unbalanced" connection. Unbalanced connections have a distance limitation of 50 ft (approximately 15 meters) and are very susceptible to noise.

Applications that Rely on Reading Serial Data

Embedded Systems

Embedded systems often provide serial ports used by engineers to program and debug their microcontrollers. Communication issues between a microcontroller and a computer are typically diagnosed by reading serial data. An example can be seen in this tutorial on reading serial data from an Arduino.

Industrial Automation

Industrial facilities often utilize serial communication to control and monitor equipment used in automated procedures. Analyzing serial data can be instrumental in diagnosing problems and optimizing system performance. Feedback from real-time data sensors can be used to make immediate adjustments in machinery parameters to address fluctuating conditions in an automated assembly line.