UART

The phyCORE-AM67x provides access to up to 9 UART interfaces that can be used for configuration and data exchange with external peripheral devices. The phyBOARD-Rigel AM67x provides access to five of these interfaces through expansion connectors.

By default, the phyBOARD-Rigel AM67x is configured to use UART0 for a Linux console input and output. The UART0 signal is available through a micro-USB connector X5 via a UART to USB bridge. PHYTEC recommends allocating UART0 for console access on custom designs. You can see all available UART interfaces in the images and tables below. To learn more information about the phyCORE-AM67x UART interface, please see sections 7.5 and 11.3 in the Hardware Manual.

The UART channels correspond to the following connectors and system paths.

UART
UART	Connector	Character Device File	Status
UART0	X49 (Micro USB), X6 (10-pin Header)	/dev/ttyS2	Default Linux Console at X49 X6 is currently unavailable
WKUP_UART0	X37 (Exp Connector)	/dev/ttyS3

Requirements

USB to TTL Cable 3 pin
3x M/M Jumper Wire

Note

The expansion header was designed for 2mm pins. It is acceptable to use 2.54mm jumper pins during the development and verification of interfaces. The only issue arises when you switch back to plugging in a 2mm male header for an expansion board you created.

Hardware Setup

Power off and remove the power supply from the phyBOARD-Rigel AM67x.
```
sh-phyboard-rigel-am67xx-1:~# poweroff
```

Connect the TTL Cable to the expansion header X37. Do not connect the cable to your host system yet.

TTL Cable and X37 Header Signals
GND	Black Connecter	Pin 7 (X37)
TXD	Orange Connecter	Pin 15 (X37)
RXD	Yellow Connecter	Pin 13 (X37)

../_images/pb-08036_wkup_uart0_pinout.webp

Power the phyBOARD-Rigel AM67x back on.
Inspect dmesg output to figure out the TTL device of the UART to USB bridge cable. If you already have connected a cable to the USB debug port, your TTL device will be very likely /dev/ttyUSB3.

Setting the Baud Rate

Before using the UART interface, you need to configure the baud rate. The following command sets the baud rate to 115200 bps for the UART interface:

sh-phyboard-rigel-am67xx-1:~# stty -F /dev/ttyS3 115200

You can verify the current settings using:

sh-phyboard-rigel-am67xx-1:~# stty -F /dev/ttyS3 -a

Sending Messages

To send data through the UART interface, you can use the echo command to write to the device:

sh-phyboard-rigel-am67xx-1:~# echo "Hello World" > /dev/ttyS3

For continuous transmission, you can use a loop:

sh-phyboard-rigel-am67xx-1:~# while true; do echo "Test Message" > /dev/ttyS3; sleep 1; done

Receiving Messages

To read incoming data from the UART interface, use the cat command:

sh-host:~$ cat /dev/ttyS3

This will display any incoming messages in real-time. Press Ctrl+C to stop reading.

For debugging purposes, you can also use minicom. Install it using:

sh-host:~$ sudo apt update
sh-host:~$ sudo apt install minicom

Start minicom:

sh-host:~$ minicom -D /dev/ttyS3 -b 115200

Booting via UART

See chapter UART on how to boot from UART.