Raspberry PI - Serial Port Output

The next thing that I wanted to do is get a Python program talking to the serial port TXD pin on the GPIO header (Pin 8) . Using the info in ref 1, here is what to do to get serial output:

 
To keep from spawning a terminal login session on the header serial port, in  the file

      /etc/inittab

 Comment out the line (using nano as discussed in previous posts)

     # 2:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

You can also stop boot up messages as per the reference, but I did not do this.

Then you need to re-boot (as the login process was spawned already, and will not be spawned until you boot with that line commented out)

    $ sudo shutdown -r now

I then found that you need to install this software package

    $ sudo apt-get install python-serial

When rebooted, log back in and nano up the following Python program as sertest.py (heavily based on ref 1, some neat tricks here, like the code to do a clean exit when you hit ^C on the controlling keyboard):

----------------------------------------------------------------

#!/usr/bin/env python
#
print ("Starting program")
import serial
import time
# import string
#
count = 1
test=serial.Serial("/dev/ttyAMA0",9600)
test.open()
teststring = "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz"
#
try:
    while True:
                print count, teststring
                test.write(teststring)
                print "Waiting 1 second"
                time.sleep(1)
                count = count + 1
#
except KeyboardInterrupt:
    pass # do cleanup here
#
test.close()

----------------------------------------------------------------

Now run it as root (to get access to the metal):

  $ sudo python sertest.py

Observing the serial TXD (header pin 8) with the logic probe, you can see a data stream while the program is running. It works!

References:

1) http://codeandlife.com/2012/07/29/arduino-and-raspberry-pi-serial-communication/

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