This page describes how the Raspberry Pi can be configured for UART communication. As the UART interface is used for a serial linux console by default, some adaptions are required to use the UART interface in other applicatiions.

Environment

The settings has been tested in the following environment:

• Raspberry Pi 4
• Rasperry Pi OS of December 2nd 2020 (2020-12-02-raspios-buster-armhf-full.zip)

Write Image

Download the image, unpack it and flash it to your SD card as described here: https://www.raspberrypi.org/software/

Configure UART usage

Before starting the Raspberry Pi the first time, modify the following files:

• Add the follwoing line at the end of /boot/config.txt

enable_uart=1

• Change /boot/cmdline.txt, remove the following text

console=serial0,115200

Optional: Enable SSH access by default

If you want to access the Raspberry Pi via SSH by default, create an empty file /boot/SSH.txt

Install Screen

After booting the Raspberry Pi, install screen:

sudo apt-get install screen

Test UART communication in loopback mode

The pins GPIO 14 (TX) and GPIO 15 (RX) are used for UART communication. For loopback testing, connect both pins to each other.

For testing, we use screen as a terminal:

screen /dev/serial0 115200

Now you should be able to enter text. If the text is shown in the screen window, the loopback test works.

For exiting screen, press Ctrl + A, than \.

References

• GPIO - Raspberry Pi Documentation
• Configuring The GPIO Serial Port On Raspbian Jessie and Stretch Including Pi 3 and 4