A serial loopback test is a way to check if a serial port is working properly by sending and receiving data from the same port. It can help diagnose hardware or software problems with serial communication. In this article, we will show you how to perform a serial loopback test on Linux using a simple program and a jumper wire.
What You Need
To perform a serial loopback test on Linux, you will need the following:
A Linux computer with a serial port (RS232 or USB-to-serial adapter)
A jumper wire or a null modem cable
A terminal emulator program (such as minicom, picocom, or screen)
A serial loopback test program (such as linux-serial-test)
How to Perform a Serial Loopback Test
Follow these steps to perform a serial loopback test on Linux:
Connect the jumper wire or the null modem cable between the transmit (TX) and receive (RX) pins of the serial port. If you are using a USB-to-serial adapter, plug it into your computer and note the device name (such as /dev/ttyUSB0).
Open a terminal emulator program and configure it to use the serial port with the correct baud rate, parity, data bits, and stop bits. For example, if you are using minicom, you can run minicom -D /dev/ttyUSB0 -b 115200 to connect to /dev/ttyUSB0 with 115200 baud rate.
Download and compile the linux-serial-test program from https://github.com/cbrake/linux-serial-test. You can use git clone https://github.com/cbrake/linux-serial-test.git to download the source code and make to compile it.
Run the linux-serial-test program with the same serial port and baud rate as the terminal emulator. For example, if you are using /dev/ttyUSB0 with 115200 baud rate, you can run ./linux-serial-test -s -e -p /dev/ttyUSB0 -b 115200. The program will send and receive data from the same port and report the number of bytes and errors.
If the serial loopback test is successful, you should see something like this on the terminal emulator: