Industrial Shields Raspberry PLC 19R+, Quick User Manual

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Rev. 8: 29-04-2021
42
A & B Zone Features: Communications & RTC & uSD
RS-485
Raspberry PLC is provided with two RS-485 channel communications. Both are half-duplex and
are controlled via the SPI0 bus.
Both RS-485 ports can be configured with the following commands:
➔
Configure the RS-485(2) port using the command
stty (baudrate) -F /dev/ttySC0
➔
Configure the RS-485(1) por using the command:
stty (baudrate) -F /dev/ttySC1
This are the baudrates accepted for both ports:
4800, 9600, 14400, 19200, 28800, 38400, 57600, or 115200
Now, that we can configure both channels we can start using these ports with the desired
programming system.
For example, we can use the following bash script instruction to see the data coming from the
RS-485(2). It will stay opened waiting for data to read. Cancel it any time pressing Ctrl + C:
cat /dev/ttySC0
Or also use the following command to send a message through the RS-485(1) port:
echo “ Test message ” > /dev/ttySC1
I2C
The I2C protocol is meant to work in a pull-up configuration. A pull-up configuration means
that when the pin is at rest (nothing connected to it) it always reads a HIGH value. In this case
it reads 3.3V when nothing is connected. The pull-up configuration is established by default in
these pins.
If it is meant to work them as a GPIO at 3.3V, it has to be considered that they are pull-up
inputs.