Re: [PARPORT] Simple C prog needed

From: Calle Be (
Date: Thu Jan 09 2003 - 19:48:03 EST

  • Next message: Tim Waugh: "Re: [PARPORT] Simple C prog needed"

    Hi there Joe,

    Many thanx for your answer. Tim's and mine mail volley continued outside of the
    mailing list and finally he answered the following:

    echo -ne \\377 | dd of=/dev/port bs=1 seek=$((3*256+7*16+8))

    which I couldn't really follow until your reply. Well, I _still_ doesn't really
    follow Tim's line but now it seems I've got myself a better way. Your

    echo -e "\577\c" > /dev/lp0

    might just be the line I'm after. What I'm trying to do is a tram sign. In
    Göteborg, Sweden (where I live), we have a traffic watch system with signs that
    tell the commuters how many minutes it's left to the arrival of the different
    busses and trams. This information is also on the internet and since I've just
    configured a floppyfw machine, that is completely devoted to just firewalling,
    I figured it could monitor the tram traffic as well. So I'll write a script
    that greps the minute information from the internet, and control eight LED
    displays by setting the data pins on the parallel port high/low. Now the only
    problem left is whether I need to strobe the IC controlling the LEDs for the
    data to be gathered. And writing that script of course.

    So, that's that. Perhaps a bit longer anser than you expected but...

    Thanx for the help! I'll tell you if it worked out!

    /Calle Be

    --- Joe Lang <> wrote:
    > Hi Calle,
    > My name is Joe Lang and I am a blind computer specialist with
    > the National Weather Service.
    > I have been reading the volley of mail messages between you,
    > the Linux parport mail list,
    > and Tim Waugh of Redhat.
    > Can you tell me to what your parallel port is connected.
    > I'm just curious.
    > As far as sending 255 to your printer port in a shell script...
    > echo 255 > /dev/lp0 will send the characters "2" then "5" then "5"
    > plus a new line character to the port.
    > I don't think that's what you want.
    > How about:
    > echo -e "\577\c" > /dev/lp0
    > The -e option tells echo to recognize the "\" character as a prefix to
    > characters requiring specialized processing.
    > The \577 is octal for 255 decimal.
    > The \c tells echo not to add a new line at the end of its output.
    > If this still doesn't provide what you need,
    > let me know,
    > we can move on and try some C programming to directly control the printer
    > port.
    > Joe

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