UART

The phyCORE-AM64x provides access to up to 11 UART interfaces that can be used for configuration and data exchange with external peripheral devices. The phyBOARD-Electra AM64x provides access to five of these interfaces through expansion connectors.

By default, the phyBOARD-Electra AM64x is configured to use UART0 for a Linux console input and output. The UART0 signal is available through a micro-USB connector X20 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-AM64x UART interface, please see sections 7.7 and 10.3 in the Hardware Manual.

phyCORE-AM64x UART phyCORE-AM64x UART

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

UART

UART

Connector

sysfs Path

MCU_UART0

X20 (Micro USB)

ttyS0

MCU_UART1

X28 (Expansion Header)

ttyS1

UART0

X20 (Micro USB)

ttyS2

UART1

X4 (10-pin Header)

ttyS3

UART3

X27 (Expansion Header)

ttyS5

UART5

X31 (mPCIe)

ttyS7

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-Electra AM64x.

    sh-phyboard-electra-am64xx-2:~# poweroff

  • Connect the DB9 Male 2x5 to RS232 Female Cable (Included in the development kit) to the X4 connector (red line indicates Pin 1)

  • Connect the USB to RS-232 serial adpater to the female end of the the DB9 cable. Do not connect the cable to your Host system yet.

    phyCORE-AM64x UART1 Pin 1

  • Power the phyBOARD-Electra AM64x 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-electra-am64xx-2:~# stty -F /dev/ttyS3 115200

You can verify the current settings using:

sh-phyboard-electra-am64xx-2:~# 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-electra-am64xx-2:~# echo "Hello World" > /dev/ttyS3

For continuous transmission, you can use a loop:

sh-phyboard-electra-am64xx-2:~# 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.