Programmatically talking to a Serial Port in OS X or Linux | I have a Prolite LED sign that I like to set up to show scrolling search queries from a apache logs and other fun statistics. The problem is, my G5 does not have a serial port, so I have to use a usb to serial dongle. It shows up as /dev/cu.usbserial and /dev/tty.usbserial . 


When i do this everything seems to be hunky-dory:



```
stty -f /dev/cu.usbserial
speed 9600 baud;
lflags: -icanon -isig -iexten -echo
iflags: -icrnl -ixon -ixany -imaxbel -brkint
oflags: -opost -onlcr -oxtabs
cflags: cs8 -parenb

```

Everything also works when I use the [serial port tool](http://www.versiontracker.com/dyn/moreinfo/macosx/24024) to talk to it.


If I run this piece of code while the above mentioned serial port tool, everthing also works. But as soon as I disconnect the tool the connection gets lost. 



```
#!/usr/bin/python

import serial

ser = serial.Serial('/dev/cu.usbserial', 9600, timeout=10) 
ser.write("<ID01><PA> \r\n") 
read_chars = ser.read(20)
print read_chars

ser.close()

```

So the question is, what magicks do I need to perform to start talking to the serial port without the serial port tool? Is that a permissions problem? Also, what's the difference between /dev/cu.usbserial and /dev/tty.usbserial?




---


Nope, no serial numbers. The thing is, the problem persists even with sudo-running the python script, and the only thing that makes it go through if I open the connection in the gui tool that I mentioned.