Hey guys! Configuring serial port settings on Ubuntu might seem a bit daunting at first, but trust me, it's pretty straightforward once you get the hang of it. Serial ports are essential for connecting various devices, from microcontrollers to older peripherals, and getting the parameters right is crucial for smooth communication. In this guide, we'll walk you through the steps to set up your serial port parameters effectively.

Understanding Serial Port Basics

Before diving into the configuration, let's quickly cover the basics. A serial port transmits data one bit at a time over a single wire (or pair of wires for differential signaling). The key parameters that define a serial connection are the baud rate, data bits, parity, and stop bits. Understanding these parameters is the first step in successfully configuring your serial port on Ubuntu.

• Baud Rate: The baud rate is the speed at which data is transmitted, measured in bits per second (bps). Common baud rates include 9600, 115200, and others. Both devices communicating over the serial port must use the same baud rate to understand each other.
• Data Bits: This is the number of bits used to represent a single character of data. Typically, this is 7 or 8 bits. The choice depends on the specific requirements of the devices communicating.
• Parity: Parity is a simple form of error checking. It can be set to even, odd, or none. When parity is enabled, an extra bit is added to each character to ensure that the total number of 1s is either even (for even parity) or odd (for odd parity). If parity is not needed, it's set to none.
• Stop Bits: Stop bits indicate the end of a character transmission. Usually, one or two stop bits are used. One stop bit is the most common setting.

Knowing these parameters, let's move on to how you can configure them on Ubuntu.

Identifying Your Serial Port

First things first, you need to identify the serial port you want to configure. In Ubuntu, serial ports are typically represented as device files in the /dev directory. Common names include ttyS0, ttyS1 (for serial ports) and ttyUSB0, ttyUSB1 (for USB serial adapters). To identify your serial port, you can use the following methods:

Using dmesg

The dmesg command displays kernel messages, which can help you identify newly connected devices. Plug in your serial device (if it's a USB serial adapter) and then run:

dmesg | grep tty

This command will show you the device name assigned to your serial port. For example, you might see something like ttyUSB0.

Listing Devices in /dev

Another way to find your serial port is by listing the devices in the /dev directory that start with tty. Use the following command:

lsof | grep '/dev/ttyS0'

This will give you a list of available serial ports. Look for the one that corresponds to your device.

Once you've identified your serial port, you're ready to configure its parameters.

Configuring Serial Port Parameters Using stty

The stty command is a powerful utility for setting and displaying serial port settings. You can use it to configure the baud rate, data bits, parity, and stop bits. Here's how:

Setting the Baud Rate

To set the baud rate, use the following command:

stty -F /dev/ttyUSB0 <baud_rate>

Replace /dev/ttyUSB0 with your serial port's device file and <baud_rate> with the desired baud rate (e.g., 9600, 115200). For example, to set the baud rate to 115200, you would use:

stty -F /dev/ttyUSB0 115200

Setting Data Bits, Parity, and Stop Bits

You can set the data bits, parity, and stop bits using the following options with stty:

• cs<n>: Set the character size to n bits (e.g., cs8 for 8 data bits).
• parenb: Enable parity generation and detection.
• parodd: Set odd parity (implies parenb).
• -parenb: Disable parity (no parity).
• cstopb: Use two stop bits.
• -cstopb: Use one stop bit (default).

For example, to set 8 data bits, no parity, and one stop bit, you would use:

stty -F /dev/ttyUSB0 cs8 -parenb -cstopb

To set 7 data bits, even parity, and one stop bit, you would use:

stty -F /dev/ttyUSB0 cs7 parenb -parodd -cstopb

To set 8 data bits, odd parity, and two stop bits, you would use:

stty -F /dev/ttyUSB0 cs8 parenb parodd cstopb

Combining Parameters

You can combine multiple parameters in a single stty command. For example, to set the baud rate to 9600, 8 data bits, no parity, and one stop bit, you would use:

stty -F /dev/ttyUSB0 9600 cs8 -parenb -cstopb

This single command configures all the necessary parameters for your serial port.

Verifying Serial Port Settings

After configuring the serial port, it's essential to verify that the settings are correct. You can do this using the stty command with the -a option, which displays all current settings for the specified serial port:

stty -F /dev/ttyUSB0 -a

This command will output a long list of settings. Look for the baud rate, data bits, parity, and stop bits to ensure they match what you configured. For example, you should see the baud rate listed, as well as settings like cs8 for 8 data bits and -parenb for no parity.

Making Changes Permanent

The settings you configure with stty are typically only valid for the current session. If you want to make the changes permanent, you need to add the stty commands to a startup script or configuration file. There are several ways to do this:

Adding to .bashrc

One common method is to add the stty commands to your .bashrc file. This file is executed every time you open a new terminal. To edit the file, use a text editor like nano or vim:

nano ~/.bashrc

Add the stty commands to the end of the file. For example:

stty -F /dev/ttyUSB0 115200 cs8 -parenb -cstopb

Save the file and exit the text editor. The next time you open a terminal, the serial port will be configured automatically. Keep in mind that .bashrc only applies to your user.

Using /etc/rc.local

Another method is to use the /etc/rc.local file, which is executed during the system startup process. This method requires root privileges. First, make sure that /etc/rc.local is executable:

sudo chmod +x /etc/rc.local

Then, edit the file with a text editor:

sudo nano /etc/rc.local

Add the stty commands before the exit 0 line. For example:

stty -F /dev/ttyUSB0 115200 cs8 -parenb -cstopb
exit 0

Save the file and exit the text editor. The serial port will be configured automatically each time the system starts. Be aware that rc.local might not be enabled by default on newer systems, so you might need to enable it separately.

Creating a Udev Rule

A more robust method is to create a Udev rule. Udev is the device manager for the Linux kernel, and it allows you to run commands when a device is connected. Create a new Udev rule file in the /etc/udev/rules.d/ directory. The file name should end with .rules, such as 99-usb-serial.rules:

sudo nano /etc/udev/rules.d/99-usb-serial.rules

Add a rule that matches your serial device and runs the stty command. You'll need to identify the vendor and product IDs of your USB serial adapter. You can find these using the lsusb command. For example:

lsusb

Look for your USB serial adapter in the list. You'll see something like Bus 001 Device 005: ID 1234:5678 VendorID:ProductID. Use these IDs in your Udev rule:

ACTION==