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I am trying to get the uart serial to work but when I try to set the parity the following error comes out.

pi@pi3:~ $ python3
Python 3.4.2 (default, Oct 19 2014, 13:31:11) 
[GCC 4.9.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import serial
>>> ser = serial.Serial('/dev/ttyS0')
>>> ser.parity=serial.PARITY_EVEN
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/serial/serialutil.py", line 347, in setParity
    if self._isOpen: self._reconfigurePort()
  File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 413, in _reconfigurePort
    termios.tcsetattr(self.fd, TERMIOS.TCSANOW, [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])
termios.error: (22, 'Invalid argument')
>>>

I've been looking for similar problems on the web but to no success. Please help!

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3
  • Some possible causes here stackoverflow.com/questions/5496195/… – Steve Robillard Jul 27 '17 at 10:07
  • 1
    You probably have a Python error, but the secondary port doesn't support parity. – Milliways Jul 27 '17 at 12:07
  • Thank you Steve and Milliways. I guess I have to reinstall Python, disable bluetooth and use the primary port. – Oldman Aug 1 '17 at 6:42
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On a Raspberry Pi 3, the /dev/ttyS0 attached to the GPIO RX/TX header pins is the less capable mini-UART and it doesn't do parity.

Relative the to more capable UART that was repurposed to Bluetooth on the wireless-capable RPi's, the port now has:

  • No break detection
  • No framing errors detection
  • No parity bit
  • No receive timeout interrupt
  • No DCD, DSR, DTR or RI signals

See https://www.raspberrypi.org/documentation/configuration/uart.md or look in section 2.2 of the datasheet at https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf

It is possible to use a /boot/config.txt directive to turn off bluetooth, or switch the UART controlling the Bluetooth.

dtoverlay=dtoverlay=pi3-disable-bt
#dtoverlay=dtoverlay=pi3-miniuart-bt

I've tested the /boot/config.txt dtoverlay=dtoverlay=pi3-disable-bt line on my Raspberry Pi Zero W and it works within python-serial minicom to set the port to 1200 7 bit, odd parity, 2 stop bits. I haven't tested the miniUART for Bluetooth on the RPi-Zero-W.

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