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POProgrammatically talking to a Serial Port in OS X or Linux
 

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    <p>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 . </p> <p>When i do this everything seems to be hunky-dory:</p> <pre><code>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 </code></pre> <p>Everything also works when I use the <a href="http://www.versiontracker.com/dyn/moreinfo/macosx/24024" rel="noreferrer">serial port tool</a> to talk to it.</p> <p>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. </p> <pre><code>#!/usr/bin/python import serial ser = serial.Serial('/dev/cu.usbserial', 9600, timeout=10) ser.write("&lt;ID01&gt;&lt;PA&gt; \r\n") read_chars = ser.read(20) print read_chars ser.close() </code></pre> <p>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?</p> <hr> <p>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.</p>
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    1. COJust last week I wrote a small Python utility to help me debug an embedded C app by reading debug information off a USB-Serial dongle, so I'd like to think that I understand PySerial pretty well. Some additional information might help diagnose the problem: * What USB-Serial driver are you using? * Are you certain that you've configured all of the serial options (baud rate, flow control, parity, stop bits, etc.) correctly before attemtping to open the serial connection from Python? * What version of PySerial are you using?
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    2. COYou don't happen to see any serial numbers after them do you? Such as: /dev/cu.usbserial-xxxxxxxxA /dev/tty.usbserial-xxxxxxxxA /dev/cu.usbserial-xxxxxxxxB /dev/tty.usbserial-xxxxxxxxB My other through was maybe there is a permissions issue of python talking to the serial port. Do you know what user your python instance is running under? And maybe what roles it has?
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      1. USNick Berardi
 

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