Troubleshooting Serial Port Interface

Serial communication is a low-level protocol for communicating between two or more devices. Normally, one device is a computer, and the other device can be another computer or a:

modem
printer
scientific instrument such as an oscilloscope or a function generator

The serial port sends and receives bytes of information in a serial fashion — 1 bit at a time. These bytes are transmitted using either a binary format or a text (ASCII) format.

For many serial port applications, you can communicate with your instrument without detailed knowledge of how the serial port works. Communication is established through a serial port object, which you create in the MATLAB^® workspace.

Supported Platforms

The serial port interface is supported on these platforms:

Linux^® 64-bit
macOS 64-bit
Microsoft^® Windows^® 64-bit

The serial port interface is supported on the same platforms as MATLAB. For updates to the list of currently supported platforms, see System Requirements for MATLAB.

Adaptor Requirements

Use RS-232 interface standard with the serial port communication. Over the years, several serial port interface standards for connecting computers to peripheral devices have been developed. These standards include RS-232, RS-422, and RS-485 — all of which are supported by the serial port object. Of these, the most widely used standard is RS-232, which stands for Recommended Standard number 232.

In this guide, it is assumed you are using the RS-232 standard.

You need to connect the two devices with a serial cable. For more information, see Connecting Two Devices with a Serial Cable.

Serial ports consist of two signal types: data signals and control signals. To support these signal types, as well as the signal ground, the RS-232 standard defines a 25-pin connection. However, most PCs and UNIX^® platforms use a 9-pin connection. In fact, only three pins are required for serial port communications: one for receiving data, one for transmitting data, and one for the signal ground. For more information, see Serial Port Signals and Pin Assignments.

Configuration and Connection

Make sure that you have the correct instrument driver installed for your device. Refer to your device documentation and the vendor website.
Make sure that your device is supported in Instrument Control Toolbox™. See Is My Hardware Supported? (Instrument Control Toolbox).

Make sure that Instrument Control Toolbox recognizes your serial ports, by using the instrhwinfo function with the serialport interface name. For example:

info = instrhwinfo("serialport")

ans = 

  HardwareInfo with properties:

           AllSerialPorts: {"COM1"}
     AvailableSerialPorts: {"COM1"}
    ObjectConstructorName: {"serialport("COM1", 38400);"}

If your computer has more than one serial port, your output would look like this:

info = instrhwinfo("serialport")

info = 

  HardwareInfo with properties:

           AllSerialPorts: [3×1 string]
     AvailableSerialPorts: [3×1 string]
    ObjectConstructorName: [3×1 string]

In this example the output listed three ports. List the available serial ports:
```
info.AvailableSerialPorts
```
```
ans = 

  3×1 string array

    "COM1"
    "COM3"
    "COM4"
```
Tip
You can also use Windows device manager to see a list of available serial ports.
Make sure you can create your serial port object. You must provide two arguments to create the object. For example, create a serial object called s using port COM1 and baud rate 9600.
```
s = serialport("COM1",9600);
```
If you do not get an error, the object was created successfully.
When you have connected, you can communicate with your device. If you have problems sending or receiving, you may need to configure communication settings such as BaudRate, DataBits, Parity, StopBits, or Terminator. Make sure you configure these communication parameters to match those of the connected device.
See Writing and Reading Text Data and Writing and Reading Binary Data for communication examples.

Other Troubleshooting Tips for Serial Port

Verify Port

Verify that the serial (COM) port is listed in Windows Control Panel > Device Manager > Ports.

Sending and Receiving

If you have problems sending or receiving, you may need to configure communication settings such as BaudRate, DataBits, Parity, StopBits, or Terminator. Make sure you configure these communication parameters to match those of the connected device.

VISA

For serial communication, you can also use VISA with a VISA resource name, as defined in a VISA vendor utility, such as Keysight Connection Expert.

Third-party Software

For troubleshooting serial port communication, you can also use a third-party serial communication software, such as PuTTY or Tera Term, to isolate the issue.

Incorrect Data

When doing binary data communication with read and write, make sure the correct data type – for example int16, uint16, double – is being used with read and write. You should use the same data type as the instrument uses.

If reading and writing data types other than uint8 or int8, make sure the ByteOrder is correct.

Documentation