External UART expansion headers¶

The MitySOM-335x Development Kit has two general purpose UART headers that allow for the connection of either RS232 or RS485/422 expansion boards. One of each expansion board is included with a development kit.

Linux Serial Port TTY Mapping¶

Expansion Port 0 - J506 = /dev/ttyO4 = GPIO 84 for TX enable
Expansion Port 1 - J505 = /dev/ttyO3 = GPIO 105 for TX Enable

You can use an application such as minicom or microcom for testing the serial communications before it is utilized in a custom application.

Serial Port TX Enable Control¶

Each of the expansion UART headers has a TX enable line for use with the RS485/422 (the RS232 does not use the line) expansion board. If you kernel is currently not configured to control the enable line itself then you will need to manually toggle this control line.

Example using J506

To Transmit from RS485:
echo "84" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio84/direction
echo "1" > /sys/class/gpio/gpio84/value
microcom -s 115200 /dev/ttyO4

To Receive from RS485:
echo "0" > /sys/class/gpio/gpio84/value
microcom -s 115200 /dev/ttyO4

RS-232 Module pinout¶

The RS-232 module [ 80-000450RI-1] is configured as a DTE device, with tx on pin 3, rx on pin 2. If you are connecting to a typical PC serial port, you will need a NULL modem cable or adapter.