Install Raspberry Pi OS on the Raspberry Pi (by using a Linux laptop)

Download the Raspberry Pi OS (previously Raspbian) image from https://www.raspberrypi.org/software/operating-systems/ Use the full version with “recommended software”. Follow the instructions on the page to burn a SD-card.

Unplug, and reinsert your SD-card to mount it. To enable SSH logging in on the Raspberry Pi, create an empty file on the named ssh in the boot partition:

touch ssh

To enable the serial port console add this line to the file config.txt in the boot partition:

enable_uart=1

The DHCP client daemon will adjust the network interface settings automatically. This interferes with the p-net control of the Ethernet interface. So if you run your Raspberry Pi as a Profinet IO-Device (NOT if you use it as a PLC) and have a serial cable, you need to add this line to /etc/dhcpcd.conf in the root file system:

denyinterfaces eth*

If you would like to change hostname from “raspberrypi” to “pndevice-pi”, change the texts in the files etc/hostname and etc/hosts in the rootfs partition.

To make sure that you subsequently are logging in to the correct Raspberry Pi, you can create a file in the home directory in the rootfs partition. Change name to something informative, for example:

touch home/pi/IAmAProfinetDevice

Unmount the SD-card, and plug it in into your Raspberry Pi. Power up the Raspberry Pi. Log in to it via a serial cable. Use the username pi and the default password raspberry.

If you do not have any serial cable (and not have disabled DCHP), connect the Raspberry Pi to your local network. Find the IP address of it by running this on a Linux machine on the network (replace the hostname if you have changed it):

ping raspberrypi.local

Verify that it is the correct machine by checking that is disappears when the power is disconnected.

Log in to it:

ssh pi@<IP>

Enter the password mentioned just above.

Connect a serial cable to Raspberry Pi

The p-net Profinet stack will change the IP-address of the Raspberry Pi when running it as an IO-Device (as requested by the PLC), why it can be inconvenient to connect to it via ssh. Using a serial cable to connect it to your laptop can then be helpful.

Use a USB-to-serial adapter cable with 3.3 V logic levels. For example Adafruit sells a popular version of those cables.

If not already done, enable the serial port console by writing the line enable_uart=1 in the file /boot/config.txt.

The serial port within the Raspberry Pi will be named /dev/ttyS0.

Pin

Name

Terminal on cable

Adafruit cable color

6

GND

GND

Black

8

UART0_TXD

RX

White

10

UART0_RXD

TX

Green

Use a communication program with a baud rate of 115200.

Before connecting the serial cable to your Raspberry Pi you can verify the functionality of the cable by connecting the USB connector to your Laptop, and connect the RX-terminal to the TX terminal of the cable. Use a communication program to verify that text that you enter is echoed back. When removing the RX-to-TX connection the echo should stop.

Optionally connect LEDs and buttons to Raspberry Pi

You need these components:

Component

Number required

LED

2

Resistor 220 Ohm

4

Button switch

2

Connect them like:

Pin

Name

Description

9

GND

11

GPIO17

Connect application data LED to GND via 220 Ohm

13

GPIO27

Connect button1 to 3.3V via 220 Ohm

15

GPIO22

Connect button2 to 3.3V via 220 Ohm

16

GPIO23

Connect Profinet status LED to GND via 220 Ohm

17

3.3V

The resistors for the buttons are to limit the consequences of connecting the wires to wrong pins.

Set up the GPIO pins for the buttons:

echo 22 > /sys/class/gpio/export
echo 27 > /sys/class/gpio/export

and for the LEDs:

echo 17 > /sys/class/gpio/export
echo 23 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio17/direction
echo out > /sys/class/gpio/gpio23/direction

Turn on and off a LED:

echo 1 > /sys/class/gpio/gpio17/value
echo 0 > /sys/class/gpio/gpio17/value

Show state of buttons:

cat /sys/class/gpio/gpio22/value
cat /sys/class/gpio/gpio27/value
_images/RaspberryPiLedButtons.jpg

Adjust IP address if using the Raspberry Pi as a PLC

If running your Raspberry Pi as a PLC (Profinet IO-Controller). you would like to have a static IP address (it will not work if running as a Profinet IO-Device). Instead modify the file /etc/dhcpcd.conf to include these lines:

interface eth0
static ip_address=192.168.0.100/24

You can still ping the <hostname>.local address to find it on the network. To re-enable DHCP, remove the lines again from /etc/dhcpcd.conf.

Advanced users only: Autostart of sample application

Use systemd to automatically start the p-net sample application on startup. Place a systemd unit file here: /lib/systemd/system/pnet-sampleapp.service

An example file is available in the sample_app/ directory of this repository. It assumes that the code is checked out into /home/pi/profinet/p-net/ on your Raspberry Pi. Install the file:

sudo cp /home/pi/profinet/p-net/sample_app/pnet-sampleapp.service /lib/systemd/system/

Adapt the contents to your paths and hardware.

Enable automatic startup:

sudo systemctl daemon-reload
sudo systemctl enable pnet-sampleapp.service

To see the status of the process, and the log output:

systemctl status pnet-sampleapp.service

journalctl -u pnet-sampleapp -b

If using a serial cable, you might need to adjust the number of visible columns:

stty cols 150 rows 40

Advanced users only: Control of built-in LEDs

The Raspberry Pi board has LEDs on the board, typically a red PWR LED and a green ACT (activity) LED.

Manually control the green LED (ACT = led0) on Raspberry Pi 3:

echo none > /sys/class/leds/led0/trigger
echo 1 > /sys/class/leds/led0/brightness

And to turn it off:

echo 0 > /sys/class/leds/led0/brightness

Note that you need root privileges to control the LEDs.

Similarly for the red (power) LED, which is called led1.