Alright, folks! Ever found yourself wrestling with serial port settings in Ubuntu? It can be a bit of a head-scratcher, but trust me, once you get the hang of it, you'll be configuring like a pro. This guide will walk you through setting those parameters, step by step, so you can get your devices communicating smoothly. Let's dive in!

Understanding Serial Ports

Before we get our hands dirty with configurations, let's get on the same page about what serial ports are and why you might need to tweak them. Serial ports, also known as COM ports in some systems, are communication interfaces that transmit data one bit at a time. They're commonly used for connecting devices like microcontrollers, GPS modules, older printers, and various embedded systems to your computer.

The need to set serial port parameters arises because different devices communicate using different settings. If your Ubuntu system isn't configured to match the device's expected settings, you'll end up with garbled data or no communication at all. The key parameters we're usually concerned with are baud rate, data bits, parity, and stop bits. Getting these right ensures that both devices can understand each other.

Why Configure Serial Port Parameters?

Configuring serial port parameters is essential for seamless communication between your Ubuntu machine and various hardware devices. Imagine trying to speak two different languages at the same time – that's what happens when serial port settings don't match! You might encounter issues like data corruption, where the information received is nonsensical, or complete failure of communication, leaving you scratching your head. By properly setting the baud rate, data bits, parity, and stop bits, you ensure that both devices are on the same page, allowing for reliable and accurate data transfer. This is particularly crucial when working with microcontrollers, GPS modules, and legacy devices that rely on specific serial communication protocols. So, taking the time to configure these settings correctly can save you a lot of frustration and ensure that your projects run smoothly.

Identifying Your Serial Port

First things first, you need to know which serial port you're dealing with. In Ubuntu, serial ports are typically named something like /dev/ttyS0, /dev/ttyUSB0, etc. The ttyS ports are usually the built-in serial ports, while ttyUSB ports are for USB-to-serial adapters. To figure out which one you need, you can use a couple of tricks.

Using dmesg

The dmesg command displays kernel messages, which can be super helpful for identifying devices as they're connected. Plug in your serial device (if it's a USB adapter) and then open a terminal. Type dmesg | tail and hit enter. This will show you the most recent kernel messages, and you should see something related to your newly connected device. Look for lines that mention ttyUSB or ttyS. The number after that will tell you the port number. For example, if you see ttyUSB0, you know you're dealing with the /dev/ttyUSB0 port.

Using ls /dev/tty*

Another straightforward way to list all available serial ports is to use the command ls /dev/tty*. This will display a list of all devices in the /dev directory that start with tty. From there, you can usually identify the correct port by process of elimination or by knowing which USB port you plugged your device into. Keep in mind that you might need to disconnect and reconnect your device to see which tty entry disappears and reappears, helping you pinpoint the right one.

Setting Serial Port Parameters with stty

Now that you know which serial port you're using, let's get down to setting the parameters. The stty command is your best friend here. It's a command-line utility for setting and displaying terminal line settings, including those for serial ports. Here’s how to use it:

Basic Syntax of stty

The basic syntax for using stty to set serial port parameters is:

stty -F <serial_port> <parameter1> <parameter2> ...

Here, <serial_port> is the path to your serial port (e.g., /dev/ttyUSB0), and <parameter1>, <parameter2>, etc., are the settings you want to configure. Let's look at some common parameters.

Common Parameters

• Baud Rate: This is the speed of data transmission. Common values include 9600, 115200, etc. To set the baud rate, use the syntax stty -F /dev/ttyUSB0 115200.
• Data Bits: This specifies the number of data bits in each byte. Common values are 5, 6, 7, and 8. To set 8 data bits, use stty -F /dev/ttyUSB0 cs8. For 7 data bits, use cs7.
• Parity: Parity is a simple form of error checking. Common options are none, even, and odd. To set no parity, use stty -F /dev/ttyUSB0 parenb -parodd. For even parity, use stty -F /dev/ttyUSB0 parenb parodd. For odd parity, use stty -F /dev/ttyUSB0 parenb parodd.
• Stop Bits: This specifies the number of stop bits at the end of each byte. Common values are 1 and 2. To set 1 stop bit, no specific command is needed as it is the default. To set 2 stop bits, use stty -F /dev/ttyUSB0 cstopb.

Example Configuration

Let's say you want to set the serial port /dev/ttyUSB0 to 115200 baud, 8 data bits, no parity, and 1 stop bit. Here’s the command you'd use:

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

Breaking it down:

• -F /dev/ttyUSB0: Specifies the serial port.
• 115200: Sets the baud rate to 115200.
• cs8: Sets 8 data bits.
• -parenb: Disables parity.
• -parodd: Ensures no odd parity is set (since parity is disabled).
• -cstopb: Sets 1 stop bit (disables 2 stop bits).

Making Changes Permanent

The settings you apply with stty are temporary and will be lost when you disconnect the device or restart your system. To make these changes permanent, you need to add the stty command to a startup script or a configuration file.

Adding to .bashrc

One common approach is to add the stty command to your .bashrc file. This file is executed every time you open a new terminal. Open .bashrc with a text editor:

nano ~/.bashrc

Add the stty command to the end of the file:

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

Save the file and exit. For the changes to take effect, either restart your terminal or run source ~/.bashrc.

Using udev Rules

For a more robust and system-wide solution, you can use udev rules. udev is the device manager for the Linux kernel, and it allows you to run scripts when devices are connected. Create a new udev rule file:

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

Add the following content, adjusting the ATTRS{idVendor} and ATTRS{idProduct} to match your device (you can find these using lsusb):

ACTION==