Document versions and changes

What is UART?

UART is a commonly used serial communication protocol in embedded systems. It is a simple interface to exchange information between two systems over short distances. The maximum transfer speed is specifed as baud (symbol per second) and can range from 9600 to several Mbaud.

Requirements

• Already flashed Jetson

• Carrierboard that supports UART

• UART cable to connect to the carrierboard

Hardware setup

Loopback

The loopback is mostly used for testing the TTY interface and is a good start to get used to it. Its only required to connect one cable from the UART TX to the UART RX signal.

System to System

If you want to communicate between two system, then you have to connect the UART RX and TX signals crossed with the ones from the other signal.

Software Setup

Minicom is a terminal tool to simplify the configuration and the usage of the UART port that you want to use.

Install minicom

In case you do not have Minicom already installed use the following command to install it on your Jetson:

Check tty device

Open minicom

Now that everything is set up get the debug logs, you just have to start Minicom with the following parameters:

Your terminal should now look like something like this

Configure TTY Port

Start Stop Bits

There is always a Start bit which starts with a low bit pulse and a Stop bit which stops with a high bit pulse. Between the Start and Stop bit are the programmable numbers of data bits (typically between 5 to 8)

Hardware Flow Control

Requirements:

• RTS data line (Request to Send)

• CTS data line (Clear to Send)

These lines are cross-connected between two devices. The RTS line is used to output if it is ready to accept new data and the CTS is used to read if it is allowed to send data to the other device.

Software Flow Control

Requirements:

• RX (Receiver)

• TX (Transmitter)

• GND (Ground)

The Transmission in a Software Flow Control is started and stopped by sending special flow control characters. The flow control character are send from the Transmitter to the Reciever line.

Special flow control characters:

• XON (Allow transmission from device, control character: DC1 ^Q, ASCII dec 17)

• XOFF (Should halt transmission from device, control character: DC3 ^S, ASCII dec 19)

Example: Jetson 1 sending XOFF to Jetson 2 => Jetson 2 should halt transmitting to A until Jetson 1 sends XON to Jetson 2

Differences

Baud rate

The baud rate is the amount of bits that get transmitted per second.

Example: 1 bit per 200 millisecond is 5 baud

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Change settings in minicom

Open you minicom terminal and press [CTRL-A] O to open up the configuration window

Press "Serial port setup" to continue

In this Panel you can configure:

Change Baudrate (E)

Toggle Hardware Flow Control (F)

Toggle Software Flow Control (G)

After changing your settings press Enter to save changes and go to Exit to close the configuration